Blood Proteins and Inflammation
in the Horse
Mark V. Crisman, DVM, MSa,*,
W. Kent Scarratt, DVMa
Kurt L. Zimmerman, DVM, ...
inflammatory and anti-inflammatory systems malfunctions, resulting in po-
tentially fatal sequelae. Inflammation that goes un...
plasma concentrations increase or decrease in response to the challenge. The
negative APP in most species is albumin, the ...
breakdown in normal remodeling. Extrahepatic production of SAA3, al-
though speculative, suggests a ‘‘housekeeping’’ role ...
during the first 48 hours of clinical signs and then returned to baseline over the
ensuing 11 to 22 days in uncomplicated c...
Hp is classified as a moderate APP, demonstrating an increase of 1 to
10 times greater than the reference inter...
Fb was one of the earliest recognized APPs. Fb, a soluble plasma glyco-
protein synthesized by the liver, is co...
more likely to be associated with chronic conditions rather than acute in-
flammation. Local (extrahepatic) AGP production ...
proteins, and the results can be a useful diagnostic aid to the clinician. There
are, however, only a few diseases for whi...
hyperthermia, and inflammation also can influence the profile of SPE [31].
Common abnormalities identified on SPE include hypo...
to have a lower concentration of albumin and a higher concentration of
alpha-2 globulin [53].
Hypoglobulinemia may be caus...
[18] Hulten C, Demmers S. Serum amyloid A (SAA) as an aid in the management of infectious
disease in the foal: comparison ...
[40] Itoh H, Tamura K, Izumi M, et al. The influence of age and health status on the serum alpha
1-acid glycoprotein level ...
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Blood proteins and inflammation in the horse


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Blood proteins and inflammation in the horse

  1. 1. Blood Proteins and Inflammation in the Horse Mark V. Crisman, DVM, MSa,*, W. Kent Scarratt, DVMa , Kurt L. Zimmerman, DVM, PhDb a Department of Large Animal Clinical Sciences, Virginia Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA b Department of Biomedical Sciences and Pathobiology, Virginia Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA 24061, USA Inflammation is often associated with systemic alterations distant from the initial insult that involve many organ systems all designed to eliminate the offending antigen. Activation of the host response to infection, the ‘‘acute-phase response’’ (APR), is a highly organized physiologic reaction that includes changes in concentrations of plasma proteins termed acute- phase proteins (APPs). The circulating concentrations of these proteins can provide an objective measure of the severity and extent of the underlying condition. The APPs are increasingly being used as markers for prognosis and monitoring response to therapy along with general determinants of equine health. Use of APPs in veterinary medicine is becoming more wide- spread as more commercial diagnostic kits are being validated. This article reviews the salient features of APPs and examines their current application and potential utility in equine inflammatory disorders. Acute-phase proteins A primary challenge in medicine involves the detection and monitoring of inflammation, which results from myriad disease processes. Inflammation is a complex process involving networks of cellular and humoral events that are pivotal for the health and survival of all organisms. Early recognition of systemic inflammation is essential to devise and implement an effective treatment plan. This is especially critical if the delicate balance between * Corresponding author. E-mail address: (M.V. Crisman). 0749-0739/08/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.cveq.2008.03.004 Vet Clin Equine 24 (2008) 285–297
  2. 2. inflammatory and anti-inflammatory systems malfunctions, resulting in po- tentially fatal sequelae. Inflammation that goes unrecognized or does not display obvious clinical signs may result in subclinical infections that subse- quently impair growth and performance. The resultant clinical deterioration may progress to sepsis, multiple organ failure, and death. It is no surprise that the search for early markers of inflammation has been the focus of hu- man and veterinary medicine over the past several decades. To this end, ef- forts have focused on biochemical identification of APPs as markers for the degree and time course of inflammation. In response to infection or injury, these proteins are quickly released into the bloodstream and their concentra- tions are directly related to the severity of the underlying condition. In gen- eral, APPs are defined as proteins whose plasma concentration increases or decreases by at least 25% after an inflammatory stimulus [1]. Quantification of these proteins can provide valuable diagnostic and prognostic informa- tion and ultimately have a major influence on the outcome of the disease process. The APR is a nonspecific, complex, highly orchestrated inflammatory re- sponse designed to minimize tissue damage; enhance the repair process; and restore homeostasis after infection, trauma, or stress. This response is stim- ulated when injured cells release arachidonic acid metabolites and products of oxidative stress, followed by elaboration of cytokines, such as interleukin (IL)-1b, IL-6, and tumor necrosis factor-a (TNFa), from macrophages and monocytes. These cytokines are responsible for many of the cardinal signs of inflammation, including pyrexia and leukocytosis. Increases in the circula- tion of these proinflammatory mediators (especially IL-6) stimulate the he- patic APR (at the expense of albumin synthesis) [2]. Included among the many roles attributed to APPs are complement activation, coagulation, fi- brinolysis, and inhibition of neutrophil proteases [1]. It is important to note that within the complex cytokine signaling network, target cells are sel- dom exposed to only a single cytokine. Combinations of cytokines on var- ious target cells may have a stimulatory or suppressive effect. For example, the elaboration of serum amyloid A (SAA) generally requires IL-6 and IL-1 or TNFa, whereas IL-1 and TNFa inhibit the induction of fibrinogen (Fb) by IL-6. Additionally, glucocorticoids typically upregulate the stimulatory effects of cytokines on the production of APPs, whereas insulin may play an inhibitory role on production of some APPs [1]. Although the APR is critical in inflammation and healing, it also functions in an ‘‘anti-inflamma- tory’’ capacity that attenuates the inflammatory response to localized stimuli. Seventy five years ago, C-reactive protein (CRP) was the first APP recog- nized in human beings, and it has subsequently become an invaluable diag- nostic tool in human medicine to detect and monitor inflammation [3]. The most frequently measured APPs in equine practice are Fb, SAA, and hapto- globin (Hp) [4]. The APPs are generally classified as ‘‘positive’’ proteins, in- cluding major or moderate, and ‘‘negative’’ proteins, depending on whether 286 CRISMAN et al
  3. 3. plasma concentrations increase or decrease in response to the challenge. The negative APP in most species is albumin, the most abundant constituent in plasma [5]. During the APR, albumin synthesis is downregulated in favor of increasing hepatic synthesis of positive APPs. The positive major APPs have the following characteristics: Low or undetectable concentrations in plasma of healthy individuals Concentrations increase greater than 10-fold rapidly during APR Express a large dynamic range Rapid decrease in concentrations with disease resolution Relapse or secondary infection results in increased concentrations Currently, only SAA fulfills the criteria of a positive major APP in horses. The positive moderate APPs have the following characteristics: Aways present in the plasma of healthy horses Concentrations increase 1 to 10 times in response to inflammation or injury Response is generally slower (days to weeks) to increase, peak, and re- turn to baseline Examples of moderate APPs in horses include Hp, Fb, a1-acid glycopro- tein (AGP), and CRP. In general, a substantial increase in plasma APP concentrations in horses has been demonstrated with viral and bacterial infections [6,7], surgery [8], colic [9], and experimentally induced arthritis [10]. Moderate changes occur after strenuous exercise, heatstroke, and parturition. Concentrations of the multiple components of the APR generally increase together, although not all increase uniformly in all horses with the same conditions. The circulating concentration of APPs can provide an objective determinant of the health of an animal, including the severity of any underlying condition, and allow monitoring of the resolution of disease. Serum amyloid A protein Equine SAA is an acute-phase apolipoprotein that increases (O100-fold) rapidly after tissue injury, infection, or inflammation [11]. Produced primar- ily by hepatocytes during the APR, several extrahepatic isoforms of SAA, specifically SAA3, have been identified in horses [10,12,13]. Extrahepatic se- cretion of SAA3 has been demonstrated in the mammary gland (colostrum) and joints (synovial fluid) from horses [13,14]. The physiologic roles of SAA are not completely understood, because various effects have been reported. These include enhancement or inhibition of leukocyte functions, chemotac- tic recruitment of inflammatory cells to the site of infection [15], inhibition of lymphocyte and endothelial cell proliferation, inhibition of platelet aggre- gation, and phagocytosis. SAA may also inhibit myeloperoxidase release and directed migration of phagocytes and modulate connective tissue 287BLOOD PROTEINS AND INFLAMMATION IN THE HORSE
  4. 4. breakdown in normal remodeling. Extrahepatic production of SAA3, al- though speculative, suggests a ‘‘housekeeping’’ role for the protein by pro- viding an immediate defense against tissue injury from inflammatory challenges. Mammary-associated SAA3 may provide a beneficial function for the suckling neonate or maintenance of the mammary gland [13]. Alter- natively, SAA is the primary precursor of amyloid A and has been impli- cated in the pathogenesis of amyloidosis [16]. Reference intervals for plasma SAA concentrations in healthy horses have been reported to range from less than 0.5 to 20 mg/L [7,14,17]. The low constitutive expression of SAA in healthy horses allows straightforward interpretation of even moderate increases in SAA concentrations after an in- flammatory stimulus. The short half-life of SAA allows accurate monitoring of disease after therapeutic intervention. Therefore, sequential SAA deter- minations may be potentially useful in patient management and prognosti- cation. The overall diagnostic sensitivity and kinetic profile of SAA (compared with moderate APPs, such as Fb) make it an ideal marker of in- flammation and tissue damage. Clinical applications of serum amyloid A Several studies have evaluated the application and efficacy of SAA in healthy and septic neonates [6,17,18]. Neonatal septicemia is one of the most challenging problems encountered by equine veterinarians; thus, rapid diagnosis and aggressive therapy have a major influence on outcome. Typ- ically, sepsis refers to disseminated gram-negative bacterial infections. Gram-positive bacterial and viral infections, trauma, hypovolemia, and hemorrhage may all activate the proinflammatory pathways, however, re- sulting in the systemic inflammatory response syndrome (SIRS) [19]. Inves- tigations have suggested that SAA is a sensitive indicator of inflammation and may be beneficial in differentiating neonatal weakness, diarrhea, and septicemia. Increased SAA concentrations have been reported in foals with various bacterial infections [18], septicemia, localized infections (in- cluding omphalophlebitis), and arthritis [17]. Higher SAA concentrations have been noted with bacterial infections, whereas viral infections elicit a more tempered response [7]. In contrast, noninfectious causes of neonatal weakness (failure of passive transfer, pre- and dysmaturity, maladjustment syndrome, and meconium impaction) have been associated with normal [17,18] to slightly increased SAA concentrations [20]. This may be attribut- able to assay variability and sampling technique. Nonetheless, it is generally agreed that SAA determinations proved superior when compared with clas- sic markers of inflammation (eg, Fb, leukocyte counts) in distinguishing in- fectious from noninfectious causes of SIRS. Concentrations of SAA in equine respiratory disease have also been evaluated, specifically equine influenza and Rhodococcus equi pneumonia. A study on equine influenza indicated that SAA concentrations increased 288 CRISMAN et al
  5. 5. during the first 48 hours of clinical signs and then returned to baseline over the ensuing 11 to 22 days in uncomplicated cases [7]. SAA determinations proved to be a more sensitive indicator of infection than nasal swabs and correlated well with disease resolution. A recent study by Cohen and colleagues [6] eval- uated SAA concentration in foals with R equi pneumonia and its utility to dif- ferentiate normal from affected foals. Results indicated that bimonthly SAA determinations in foals less than 1 month of age were not a useful screening tool for R equi infection. This may have been attributable to the nature of the disease (insidious with walled off pulmonary abscesses) or the long sampling interval. Regardless, more research is needed in this area to determine conclu- sively the usefulness of SAA in foals with R equi pneumonia. Concentrations of SAA have been determined in horses with colic result- ing from inflammatory and noninflammatory causes. Horses with colic attributable to inflammatory causes (enteritis, peritonitis, colitis, or abdom- inal abscesses) had significantly higher concentrations of SAA than horses with noninflammatory causes (displacement or obstruction). Additionally, SAA concentrations were higher in horses that failed to survive the colic ep- isode compared with survivors; however, the difference was not substantial enough to be clinically useful at this time [9]. Studies of SAA response to equine joint disease have been recently per- formed on serum and synovial fluid [21]. SAA concentrations in serum and sy- novial fluid were lower than assay detection limits in healthy horses. Synovial fluid and serum SAA concentrations were significantly elevated in horses with suspected infectious arthritis and tenovaginitis, suggesting that SAA may be a useful biologic marker for horses with joint disease. This study corroborated an earlier project using an experimentally (lipopolysaccharide) induced arthri- tis, in which increases in synovial fluid SAA reflected inflammatory activity and concentrations decreased during stages of clinical improvement [10]. Recently, an excellent review of equine SAA was published detailing many of the salient features associated with APPs [22]. Analysis of serum amyloid A Previously, SAA measurements were primarily the domain of research laboratories. Several methodologies have been used for determining equine SAA, including ELISA [11], slide-reversed passive latex agglutination [23], and latex agglutination immunoturbidimetric assay [17]. A commercially de- veloped immunoturbidimetric assay for human SAA (LZ test SAA, EIKEN LZ-serum amyloid A assay, Mast Group, Merseyside, United Kingdom) has recently been evaluated for use in horses [14]. This rapid automated assay demonstrated good precision and is appropriate for determining equine SAA. A system has been developed in Europe to allow small diagnostic lab- oratories to measure equine SAA in 30 minutes (Equinostic, DN, EVA, Equibnostic, Copenhagen, Denmark). According to company literature, this equine SAA test is rapid and precise. 289BLOOD PROTEINS AND INFLAMMATION IN THE HORSE
  6. 6. Haptoglobin Hp is classified as a moderate APP, demonstrating an increase of 1 to 10 times greater than the reference interval in horses during the APR (ref- erence interval: 2–10 g/L). Hp is classified as a major APP in ruminants and has been proved to be an effective marker for the presence and sever- ity of such diseases as mastitis, pneumonia, and endocarditis in cattle [24]. Produced primarily by hepatocytes, Hp is an a2-globulin that primarily functions to prevent the loss of iron by the formation of stable complexes with free hemoglobin (Hb) in the blood. Hp synthesis is stimulated by the Hb concentration in plasma, and the resultant Hp-Hb complex provides an efficient means for collection of free Hb, which prevents external leak or loss of iron and ameliorates the oxidative damage to tissues asso- ciated with free Hb (from hemolysis). Additionally, the Hp-Hb complexes are large enough to reduce renal filtration of free Hb and iron substan- tially from plasma. These complexes are removed by hepatocytes, allowing reutilization of iron and amino acids. Although several functions have been ascribed to Hp, it is believed to have a bacteriostatic effect by lim- iting the availability of iron, which is essential for bacterial growth. Hp may also have anti-inflammatory actions by protecting against reactive oxygen species and inhibiting granulocyte chemotaxis and phagocytosis [24]. Hp is also reported to aid in wound repair by stimulating angiogen- esis [25]. Clinical application of haptoglobin As an APP, Hp concentrations increase during any inflammatory process (eg, infection, stress, trauma, allergy). Increased serum Hp concentrations in horses have been observed after surgery [26], noninfectious arthritis [4], and carbohydrate-induced laminitis [27]. Horses with colic did not demonstrate an increase in Hp concentrations [28]. Serum concentrations of Hp can be influenced by factors other than the APR, however. Increased concentra- tions of free Hb in serum (ie, acute hemolytic event) are followed by a sub- stantial decline in concentration of free Hp, because it is quickly consumed during such hemolytic syndromes. Therefore, serum Hp concentration may be a sensitive indicator of intra- or extravascular hemolysis and infection or inflammation in horses [26,29]. Analysis of haptoglobin Currently, techniques used to determine equine Hp concentrations are fairly laborious and generally restricted to research laboratories. Techniques include single radial immunodiffusion (SRID) [30], serum protein electro- phoresis (SPE; increased a2-globulin fraction) [31], Hb-Hp binding capacity assay [4], and immunoturbidimetry [32]. A method for estimation of serum Hp using capillary zone electrophoresis has also been described [33]. 290 CRISMAN et al
  7. 7. Fibrinogen Fb was one of the earliest recognized APPs. Fb, a soluble plasma glyco- protein synthesized by the liver, is considered a moderate APP with concen- trations increasing 1- to 10-fold over 24 to 72 hours after the induction of inflammation. The relatively wide reference interval for Fb concentrations in healthy horses (200–400 mg/dL, 2–4 g/L) and lengthy response period af- ter an inflammatory stimulus have rendered Fb a fairly insensitive APP. Sev- eral functions have been ascribed to Fb, including providing a substrate for fibrin formation in tissue repair and providing a matrix for migration of in- flammatory-related cells. Fb binds to cell surface integrins (CD11/CD18) of phagocytes, initiating a cascade of intracellular signals promoting the en- hancement of degranulation, phagocytosis, and antibody-dependent cyto- toxicity. Over the past several decades, Fb has been used to diagnose and monitor various inflammatory conditions in horses. A recent study evaluat- ing serum iron and plasma Fb concentrations in systemic inflammatory dis- eases in horses concluded that an increase in Fb concentration was associated with a poor prognosis. Hypoferremia was a more accurate reflec- tion of acute, subacute, and chronic inflammation in sick horses older than 2 months of age, however [34]. Plasma Fb concentrations have been used to detect and monitor R equi pneumonia in foals. Measurement of Fb concen- trations and leukocyte counts proved useful for early identification of R equi–infected foals, although leukocyte counts proved superior under field conditions [35]. Another study evaluated SAA and Fb concentrations in healthy horses experimentally infected with Streptococcus zooepidemicus and monitored the progression of pneumonia. Results indicated that SAA responded more rapidly than Fb to changes in clinical signs of pneumonia [36]. Together, these studies suggest that an alteration in Fb concentration is not necessarily in agreement with actual disease detection or progression. Although determination of plasma Fb concentration has long been used for detecting inflammatory diseases in horses, its relatively slow APR after an inflammatory insult seriously hampers its clinical utility. Nevertheless, Fb measurements are relatively easy and inexpensive, and this fact has likely se- cured its continued wide use in veterinary medicine. Analysis of fibrinogen A heat precipitation method is used as a quick estimate of Fb concentration [37]. More accurate methods include modifications of the Ratnoff- Menzie assay, measurement of clot weight, and quantification of immunopre- cipitate formed with specific anti-Fb antiserum. a1-acid glycoprotein AGP is a highly glycosylated protein synthesized and secreted primarily by hepatocytes. It is considered a moderate APP in most species and is 291BLOOD PROTEINS AND INFLAMMATION IN THE HORSE
  8. 8. more likely to be associated with chronic conditions rather than acute in- flammation. Local (extrahepatic) AGP production has been confirmed and is believed to contribute to the general maintenance of homeostasis by reducing tissue damage associated with inflammation, particularly in ep- ithelial and endothelial cells [38]. Two major functions have been attributed to AGP, namely, drug binding and immunomodulation. Similar to albumin, AGP is capable of binding to endogenous or exogenous substances, such as heparin, histamine, serotonin, and steroids [38]. This critical function may keep total drug-binding levels constant during the APR, whereas albumin, a negative APP, decreases in total concentration. AGP has been reported to inhibit neutrophil activation, increase secretion of IL-1 receptor antago- nist by macrophages, and enhance clearance of lipopolysaccharide by di- rectly binding and neutralizing the latter [38,39]. Although AGP has been proved to be a useful APP in other species, in- cluding pigs [40] and cattle [41,42], little work has been done in horses. One study reported increased concentrations of AGP (as determined by SRID) in colts 2 to 3 days after castration and in adult horses after jejunojejunos- tomy and return to baseline values 14 to 28 days later [43]. Another study evaluating a carbohydrate overload model of laminitis in ponies reported in- creased concentrations of AGP 4 hours after administration of carbohy- drate (24 hours before the onset of clinical lameness) [27]. C-reactive protein CRP has been well documented as an APP in human beings, ruminants, dogs, and, to a lesser degree, horses [1,24]. It is considered to be a moderate APP in horses, with a two- to threefold increase over several days. CRP has several proinflammatory effects, including activation of the complement cas- cade, induction of inflammatory cytokines, and phagocytosis. CRP also has significant anti-inflammatory effects, such as inhibiting chemotaxis and the generation of superoxide by neutrophils and preventing the adhesion of neu- trophils to endothelial cells. Studies conducted in the early 1990s suggested that high CRP concentrations occurred in horses with pneumonia, enteritis, and arthritis [44]. Serum protein electrophoresis Serum proteins consist of albumin and globulins, which usually are quan- titated on a standard biochemical profile. In contrast to albumin, which is a single type of protein, globulins are a mixture of proteins that tend to mi- grate in groups on SPE [31]. These groups are known as a-globulins, b-glob- ulins, and g-globulins. The first step to investigate an increase or decrease in total serum globulins, as noted on the biochemical profile, is to perform SPE [31]. SPE is the current standard method for the fractionation of serum 292 CRISMAN et al
  9. 9. proteins, and the results can be a useful diagnostic aid to the clinician. There are, however, only a few diseases for which the pattern of SPE is pathogno- monic [31]. The principle of the electrophoretic separation of serum proteins is based on the migration of charged proteins in an electric field [31]. The direction and rate of migration of a protein are based on the type of charge (anion or cation) and size of the protein. A ‘‘normal’’ equine SPE consists of six fractions, including albumin, a1-globulin, a2-globulin, b1-globulin, b2-glob- ulin, and g-globulin. The electrophoretogram is stained, and a densitometer is used to deter- mine the proportion of proteins in these fractions, which are then used in conjunction with the total serum protein concentration to determine specific concentrations of the fractions. Reference values for these fractions on SPE of the adult horse are albumin (26–37 g/L), a1-globulin (0.6–7 g/L), a2-glob- ulin (3–13 g/L), b1-globulin (4–16 g/L), b2-globulin (3–9 g/L), g-globulin (6–19 g/L), and total serum protein (52–79 g/L) [31]. Albumin is the most prominent of the normal serum proteins on SPE and constitutes approximately 50% of the total serum protein [31]. The albumin fraction migrates closest to the anode and is the most homogeneous fraction on SPE [31,45]. Equine serum often has a minor postalbumin fraction, which appears as a shoulder on the cathodal side of the albumin peak. This shoulder often becomes more prominent with hypoalbuminemia [31]. The a-globulin fraction is the most rapidly migrating fraction of the glob- ulins and migrates as a1- (fast) and a2- (slow) globulin fractions [31]. The a1- and a2-globulin fractions are identified as the first two peaks after albumin on SPE. Important a1- and a2-globulins include antitrypsin, high-density li- poprotein, very-low-density lipoprotein, macroglobulin, ceruloplasmin, and Hp [31]. The b-globulin fraction trails the a-globulin fraction on SPE and mi- grates as b1- (fast) and b2- (slow) globulin fractions [31]. The b1- and b2- globulin fractions are identified as the third and fourth peaks after albumin on SPE. Important b-globulins include complement (C3, C4), transferrin, ferritin, and CRP. Some of the immunoglobulins (IgM and IgA) can mi- grate in the b-globulin region [31]. The g-globulin fraction trails the b-globulin fraction on SPE and includes IgG, IgA, IgM, and IgG subclass T (IgG [T]). The concentrations of these immunoglobulins in horses have also been quantitated by SRID [46]. Interpretation of serum protein electrophoresis The profile of SPE and the absolute values of the individual fractions oc- casionally can be used to make a diagnosis but are often used to direct ad- ditional diagnostic tests. The profile of SPE in an individual animal is relatively constant but may be influenced by age, hormones, pregnancy, and lactation [31]. A deficiency of dietary protein, hypothermia, 293BLOOD PROTEINS AND INFLAMMATION IN THE HORSE
  10. 10. hyperthermia, and inflammation also can influence the profile of SPE [31]. Common abnormalities identified on SPE include hypoalbuminemia, hyper- globulinemia, and hypoglobulinemia. Hypoalbuminemia is caused by a decreased synthesis or an increased loss of albumin. Albumin is synthesized in the liver, and hypoalbuminemia is a feature of chronic diffuse liver disease [31,45]. A prominent postalbumin fraction on SPE, with or without hypoalbuminemia, has been considered pathognomonic for liver disease in the horse. An increased loss of albumin may be caused by renal or gastrointestinal disease and accumulation within the thoracic or abdominal cavity [31,45]. Hyperglobulinemia is caused by an increase in the a-, b-, or g-globulin fractions and occurs in a variety of disorders. An increase in the a-globulin fraction occurs in acute inflammatory disorders, because the APPs, includ- ing SAA and macroglobulin, migrate in the a-globulin fraction [31]. An in- crease in the b-globulin fraction occurs in active liver disease, because transferrin and IgM migrate in the b-globulin fraction [31]. An increase in the beta and gamma globulin fractions (beta-gamma bridging) on SPE is noted when there is no clear separation between the beta-2 and gamma glob- ulin fractions. Beta-gamma bridging may be caused by an increase in IgM or IgA, chronic active hepatitis, or lymphosarcoma [31,45]. Experimental infec- tions of the intestinal tract with Strongylus vulgaris larvae have been asso- ciated with an increased concentration of IgG (T) [47,48]. Hypergammaglobulinemia may be caused by a broad increase (poly- clonal gammopathy) or a sharp increase (monoclonal gammopathy) in gamma globulins. The broad increase in gamma globulins that characterizes a polyclonal gammopathy is caused by the heterogeneity of clones of plasma cells, which produce a heterogeneous mix of immunoglobulins. Any or all of the immunoglobulin groups can be increased. A polyclonal gammopathy often is associated with a chronic inflammatory disease, such as hepatitis, pleuropneumonia, immune-mediated disease, neoplasia, or a chronic suppu- rative disorder [31,45]. A monoclonal gammopathy is characterized by a sharp increase (or spike) in one of the immunoglobulins. The monoclonal spike is caused by a single clone of plasma cells that produces a single class of immuno- globulin or an immunoglobulin fragment (referred to as a paraprotein, M protein, or M component), which can be identified by the results of electrophoresis, immunoelectrophoresis, or immunodiffusion [31,49,50]. Monoclonal gammopathy occurs infrequently in the horse and has been associated with plasma cell myeloma [49], malignant lymphoma [51] and idiopathic causes [52]. The diagnostic and prognostic value of SPE in horses with chronic diar- rhea was reported [49]. Horses with larval cyathostomiasis had significantly higher levels of beta-1 globulin. A normal concentration of beta-1 globulin was not a reliable indicator of the absence of larval cyathostomiasis, how- ever. Horses with chronic diarrhea that did not survive were more likely 294 CRISMAN et al
  11. 11. to have a lower concentration of albumin and a higher concentration of alpha-2 globulin [53]. Hypoglobulinemia may be caused by a reduction in the alpha, beta, or gamma globulin fractions and occurs in a variety of disorders. Failure of passive transfer of immunity in foals is associated with a deficiency of gamma globulin. A horse with a protein-losing gastroenteropathy often has hypoglobulinemia and hypoalbuminemia. References [1] Gabay C, Kushner I. Acute-phase proteins and other systemic responses to inflammation. N Engl J Med 1999;340:448–54. [2] Eckersall PD. Recent advances and future prospects for the use of acute phase proteins as markers of disease in animals. Rev Med Vet 2000;151:577–84. [3] Pepys MB. C-reactive protein fifty years on. Lancet 1981;1(8221):653–7. [4] Hulten C, Gronlund U, Hirvonen J, et al. Dynamics in serum of the inflammatory markers serum amyloid A (SAA), haptoglobin, fibrinogen and alpha2-globulins during induced non- infectious arthritis in the horse. Equine Vet J 2002;34:699–704. [5] Allen BV, Kold SE. Fibrinogen response to surgical tissue trauma in the horse. Equine Vet J 1988;20:441–3. [6] Cohen ND, Chaffin MK, Vandenplas ML, et al. Study of serum amyloid A concentrations as a means of achieving early diagnosis of Rhodococcus equi pneumonia. Equine Vet J 2005;37:212–6. [7] Hulten C, Sandgren B, Skioldebrand E, et al. The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection. Acta Vet Scand 1999;40:323–33. [8] Pollock PJ, Prendergast M, Schumacher J, et al. Effects of surgery on the acute phase re- sponse in clinically normal and diseased horses. Vet Rec 2005;156:538–42. [9] Vandenplas ML, Moore JN, Barton MH, et al. Concentrations of serum amyloid A and li- popolysaccharide-binding protein in horses with colic. Am J Vet Res 2005;66:1509–16. [10] Jacobsen S, Niewold TA, Halling-Thomsen M, et al. Serum amyloid A isoforms in serum and synovial fluid in horses with lipopolysaccharide-induced arthritis. Vet Immunol Immu- nopathol 2006;110:325–30. [11] Hulten C, Tulamo RM, Suominen MM, et al. A non-competitive chemiluminescence en- zyme immunoassay for the equine acute phase protein serum amyloid A (SAA)da clinically useful inflammatory marker in the horse. Vet Immunol Immunopathol 1999;68:267–81. [12] Hulten C, Sletten K, Foyn Bruun C, et al. The acute phase serum amyloid A protein (SAA) in the horse: isolation and characterization of three isoforms. Vet Immunol Immunopathol 1997;57:215–27. [13] McDonald TL, Larson MA, Mack DR, et al. Elevated extrahepatic expression and secretion of mammary-associated serum amyloid A 3 (M-SAA3) into colostrum. Vet Immunol Immu- nopathol 2001;83:203–11. [14] Jacobsen S, Kjelgaard-Hansen M, Hagbard Petersen H, et al. Evaluation of a commercially available human serum amyloid A (SAA) turbidometric immunoassay for determination of equine SAA concentrations. Vet J 2006;172:315–9. [15] Xu L, Badolato R, Murphy WJ, et al. A novel biologic function of serum amyloid A. Induc- tion of T lymphocyte migration and adhesion. J Immunol 1995;155:1184–90. [16] Uhlar CM, Whitehead AS. Serum amyloid A, the major vertebrate acute-phase reactant. Eur J Biochem 1999;265:501–23. [17] Stoneham SJ, Palmer L, Cash R, et al. Measurement of serum amyloid A in the neonatal foal using a latex agglutination immunoturbidimetric assay: determination of the normal range, variation with age and response to disease. Equine Vet J 2001;33:599–603. 295BLOOD PROTEINS AND INFLAMMATION IN THE HORSE
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