Plasma protein composition and function

Plasma protein composition and function

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  PLASMA PROTEIN COMPOSITION AND ITSFUNCTION Dipesh Tamrakar M.Sc. Clinical Biochemistry 1
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  OVERVIEW Introduction Functions Electrophoretic characteristics Various plasmaproteins 2
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  Plasma is aStraw colored liquid portion of blood It is obtained as supernatant when anticoagulated blood is centrifuged leaving the cell components as precipitate. 55–60% of blood is made up of plasma. consists of: water, electrolytes, metabolites, nutrients, hormones, immunoglobulins and other proteins. Plasma proteins constitute approx. 4% of the body’s total protein. INTRODUCTION 3
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  Almost all plasmaproteins, except immunoglobulins are synthesized in liver Plasma proteins are generally synthesized on membrane-bound polyribosomes Most plasma proteins are glycoproteins In lab, separation of plasma proteins can be done by salting out methods. Fibrinogen is precipated by 10% and globulin by 22% of conc Sodium Sulfate NH4SO4 precipitates globulins at half saturation and albumin at full saturation. INTRODUCTION 4
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  TOTAL PLASMA PROTEINS •Thenormal serum total protein level is 60-80 g/L. •The type of proteins in serum include: a. Albumin (35-50 g/L) b. Globulins (25-35 g/L) α− globulin: α1 & α2−globulins β− globulin: β1 & β2 globulins γ− globulins c. Fibrinogen (2-4 g/L) A/G ratio: 1.2:1 - 1.5:1. 5
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  FUNCTIONS OF PLASMA PROTEINS 1.Transport 2. Osmotic regulation 3. Catalytic function 4. Protective function 6
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  SPECIFIC FUNCTION OF SOMEPROTEIN PROTEIN PLASMA CONC. FUNCTION Pre-albumin 25 – 30 mg/dl Transport thyroxine to some extend, Indicator of nutrition Albumin 3.5 – 5.0 g/dl Transports fatty acids, bilirubin, calcium, many drugs etc., colloid oncotic pressure α1-globulin α1-antitrypsins 0.3 – 0.5 g/dl <0.2 g/dl combines with elastase, trypsin and protects the hydrolytic damage of tissues such as lungs Orosomucoid <0.1 g/dl Binds with progesterone Retinol binding protein (RBP) 3 – 6 mg/dl Transport Vit A Thyroxine binding globulin 1 – 2 mg/dl Transports thyroid hormones 7
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  PROTEIN PLASMA CONC.FUNCTION Transcortin or Cortisol binding protein (CBG) 3 – 4 mg/dl Major transporter of steroid hormones (eg; cortisol, corticosterone) α2-globulins a) Ceruloplasmin b) Haptoglobulin 0.4 – 0.8 g/dl 0.15 – 0.60 g/l <0.3 g/dl -Copper transport -Binds with plasma free haemoglobin α2-macroglobulin 0.2 – 0.3 g/dl Transports antitrypsin and antiplasmin activity Prothrombin <0.02 g/dl Participate in blood coagulation Fibrinogen 0.2 – 0.4 g/dl Participate in blood coagulation CRP 0.01 g/l Acute phase reactant: motivates phagocytosis in inflammatory disease 8
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  PROTEIN PLASMA CONC.FUNCTION β-Globulins a. Transferrin b. Hemopexin c. Plasminogen d. - Lipoproteins 0.6 – 1.1 g/dl 0.2 – 0.3 g/dl <0.1 g/dl <0.05 g/dl 0.2 – 0.5 g/dl transport Iron transport Haem involves in Fibrinolysis transport Triglycerides and cholesterol γ-Globulin a. Ig A b. Ig M c. Ig G d. Ig E e. Ig D. 0.8 – 1.8 g/dl 150 – 400 mg/dl 50 – 200 mg/dL 800-1500 mg/dL 0.02 – 0.05 mg/dl 1 – 10 mg/dl Antibody functions protects the body surface humoral immunity, serves as first line of defense mostly humoral immunity humoral sensitivity & histamine release B-cell receptor C4 complement C3 complement 0.20 – 0.65 g/l 0.55 –1.80 g/l 0.15 g/l Immune response Immune response Immune response 9
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  Electrophoresis Migration of thecharged molecules in an electric field. Negative charged particles (anions) move towards anode and positively charged particles (cations) move towards cathode. Proteins contain charges due to the presence of amino group (NH3+) and carbonyl group (COO-) All major serum proteins carry a net negative charge at pH 8.6 and migrate toward the anode. In agar gel electrophoresis, normal serum is separated into 5 bands. 1) Albumin : 55 - 65% 2) Alpha-1-globulin : 2 - 4% 3) Alpha-2-globulin : 6 -12% 4) Beta-globulin : 8 -12% 10
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  Electrophoresis Albumin has themaximum mobility (obvious band) and gamma globulin has the minimum mobility. α-1-globulins consist almost entirely of α1- antitrypsin and α1-antichymotrypsin. α2-globulins consist mainly of α 2- macroglobulin and haptoglobin. β-globulins often separate into two; β1; transferrin with a contribution from low density lipoprotein (LDL), and β2; C3 component of complement. γ-globulins are immunoglobulins; some11
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  Electrophoresis The width ofthe band depends on the number of proteins present in that fraction. Homogeneous protein gives a narrow band. stained with dyes such as Ponceau S or Amido black or Coomassie blue. cleared transparent medium scanned in densitometer light is transmitted through it to a phototube to record the absorbance of the dye that is bound to each protein fraction. absorbance is recorded on a strip-chart recorder 12
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  ABNORMAL PATTERNS INCLINICAL DISEASES Chronic infections gamma globulins are increased (smooth and widebased) Multiple myeloma sharp spike of M-band noted between beta and gamma Fibrinogen (If plasma is used) prominent band in the gamma region, which may be confused with the M-band Primary immune deficiency Gamma globulin fraction is reduced Nephrotic syndrome alpha-2 fraction (containing macroglobulin) will be very prominent. Cirrhosis of liver there are some fast-moving gamma-globulins that prevent resolution of the β- and gamma-globulin bands. 15
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  ABNORMAL PATTERNS INCLINICAL DISEASES Inflammatory condition Decrease in albumin, and increase in acute phase reactants like α1-globulins (α1-acid glycoprotein, α1- antitrypsin), α2-globulins (ceruloplasmin and haptoglobin), and β-globulin band (C-reactive protein) Chronic lymphatic leukemia gamma globulin fraction is reduced Alpha-1-antitrypsin deficiency alpha-1 band is thin or even missing 16
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  PREALBUMIN (TRANSTHYRETIN)migrates ahead ofalbumin in the electrophoresis of serum Molecular weight 55000 Dalton transport protein for thyroxine and triiodothyronine it also binds with retinol-binding protein that transports retinol (vitamin A) and is rich in tryptophan Decrease hepatic damage acute-phase inflammatory response tissue necrosis malignancy Increase patients receiving steroids alcoholics, in chronic renal failure 17
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  ALBUMIN name is derivedfrom the white precipitate formed when egg is boiled (Latin, albus = white). M.W: 69,000 D. Consists of single polypeptide chain of 585 a.a. with 17 disulfide bonds & High net negative charge at physiological pH. Constitutes  60% of the total plasma protein; most abundant plasma protein. Half-life: 20 days. Secondary structure  >50% is in the α-helical conformation.  15% as β-pleated structure  and remaining in random coil conformation. The tertiary structure - globular protein. 18
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  Synthesis by the liver.(exception- early fetal life; by yolksac) synthesis- 12 g/day Synthetic rate controlled by  Colloidal Osmotic Pressure (primarily)  protein intake ( secondarily) inflammatory cytokines decrease synthesis release decreases by hypokalemia. Catabolism by pinocytosis by all tissue  lysosomal catabolism Small amounts ( 10-20%) lost in GIT and the glomerular filtrate. Distribution 2 Compartments: intravascular (40%) & extravascular (60%). 19
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  Albumin leaves thecirculation at a rate of 4%–5% of total intravascular albumin per hour - transcapillary escape rate (TER) Albumin is responsible for nearly 80% of the colloid osmotic pressure of the intravascular fluid, It maintains the appropriate fluid balance in the tissue. Transport: (4 binding sites on albumin): bilirubin, free fatty acid, Phospholipids, cholesterol, amino acid steroid hormones, thyroine drugs (sulfonamides, aspirin, salicylate, phenytoin)  metal ions Ca2+ , Cu2+ Buffering action: Albumin has a total of 16 histidine residue that conributes to its buffering action. Nutritional function : serves as a source of amino20
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  CLINICAL SIGNIFICANCE Decrease conditions: malnutritionand malabsorption Liver disease, resulting in decreased synthesis Protein-losing enteropathy Renal failure burns or exfoliative dermatitis Hypothyroidism Acute disease states Mutation resulting from an autosomal recessive trait causing analbuminemia or bisalbuminemia Redistribution by hemodilution, Increased condition : Seldom; clinically important  with dehydration or  after excessive albumin infusion. 21
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  CLINICAL APPLICATIONS Albumin–fatty acidcomplex cannot cross BBB and hence fatty acids cannot be taken up by brain. Calcium level in blood is lowered in hypoalbuminemia. Calcium is lowered by 0.8 mg/dl for a fall of 1 g/dl of Albumin. Human albumin is therapeutically useful to treat burns, hemorrhage and shock. Hypo-albuminemia will result in tissue edema (Starling's law). In micro-albuminuria or pauci-albuminuria, small22
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  GLOBULINS M.W.: 90,000 to13,00,000 Site of synthesis α-and β-globulins are synthesized in the liver. But γ-globulins are synthesised by plasma cells. α-Globulins are glycoproteins classified into α1 and α2 depending on their electrophoretic mobility 23
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  1. α1-acid glycoprotein Alsocalled as orosomucoid Is negatively charged even in acid solutions 183 amino acids; 40 kDa; 45% is carbohydrate, including about 12% sialic acid produced by the liver half -life of about 3 days is an acute-phase reactant Normally present in 0.6 - 1.4 g/l Functions: transport protein for progesterone and basic drugs carry needed carbohydrate constituents to the sites of tissue repair following injury. 24
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  CLINICAL IMPORTANCE Increase in acuteand chronic inflammatory diseases cirrhosis of the liver malignant conditions stress, acute myocardial infarction, trauma, pregnancy, pneumonia, rheumatoid arthritis, and surgery. Decrease In generalised hypoproteinaemic conditions, hepatic diseases malnutrition nephrotic syndrome. 25
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  2. α1-Antichymotrypsin a memberof the serine proteinase inhibitor (serpin) family. Inhibits cathepsin G, pancreatic elastase, mast cell chymase, and chymotrypsin. produced in the liver. is an acute-phase protein. Decreased in liver disease. Associated with Alzheimer disease as it is an integral component of the amyloid deposits in Alzheimer disease 26
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  3. GC -GLOBULIN (GROUP-SPECIFIC COMPONENT; VITAMIN D–BINDING PROTEIN) 27 major carrier protein of vitamin D and its metabolites in the circulation (importance for bone formation and immune system) also transports fatty acids and endotoxin Gc may act as a co-chemotactic factor in facilitating chemotaxis of neutrophils and monocytes in inflammation. Increase third trimester of pregnancy Patients taking estrogen therapy oral contraceptives Decrease
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  4. α1-fetoglobulin (AFP) presentin high concentrations in fetal blood during mid-pregnancy decrease gradually after birth, reaching adult levels by 8–12 months. In normal fetuses, AFP binds the hormone estradiol. Normal adult blood level : <1 μg/dl. May increase during pregnancy Marker of hepatocellular carcinoma or teratoblastomas elevated AFP level :- spina bifida, neural tube defects, abdominal wall defects, anencephaly Low levels of maternal AFP:- increased risk for Down syndrome and trisomy 18, neural tube defects. 28
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  5. α1-antitrypsin (α1-AT) Synthesizedby hepatic parenchymal cells. principal protease inhibitor (Serpin family) of human plasma inhibits trypsin, elastase M.W.: 45,000 to 54,000 Normal value in adults: 2 to 4 g/L Physiologically, it is the most important inhibitor of leukocyte elastase released during phagocytosis by leucocytes (protective role) if deficiency of AAT is present, unchecked action of the leukocyte elastase cleaves elastin, which is important for maintaining the architecture o lung tissue. Loss of elastin leads to emphysema. 29
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  Α1-ANTITRYPSIN DEFICIENCY HASBEEN IMPLICATED IN 2 DISEASES: EMPHYSEMA AND Α1-ANTITRYPSIN DEFICIENCY LIVER DISEASE Increase one of the acute phase reactant (APR), so increased in trauma, burns, infarction, malignancy, liver disease, etc. Pregnancy contraceptive medication Decrease In protein losing disorders, e.g. nephrotic syndrome diffuse hypoproteinaemias juvenile cirrhosis of liver Respiratory diseases emphysema 30
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  Emphysema: (emphusanG=to inflate) Abnormaldistension of lungs by air Associated with lung infections and increase in activity of macrophages to release elastase that damage lung tissues In the normal circumstances, elastase activity is inhibited by α1-antitrypsin Effect of smoking on α1-antitrypsin: the a.a methionine at position 358 is involved in binding with protease Smoking causes oxidation of this methionine to methionine sulfoxide As result α1-antitrypsin with methionine sulfoxide cannot bind and inactivate proteases 31
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  32 α1-antitrypsin deficiency liverdisease: Due to accumulation of mutant α1-antitrypsin which aggregates to form polymers Aggregation is due to formation of loop-sheet polymerization hepatocytes cannot secrete these polymers. These polymers in turn cause liver damage (unknown mechanism) followed by cirrhosis Role as a tumour-marker α1-AT increased in germ cell tumours of testes and ovary As an Inhibitor of Fibrinolysis α1-AT is one of the most important inhibitors to fibrinolysis along with α2-antiplasmin and α2-
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  Α2-GLOBULINS 1.Alpha-2-Macroglobulin (AMG) major componentof alpha-2 globulins large plasma glycoprotein (M.W.: 720 kD). tetrameric protein (made up of four identical subunits of 180 KD). Synthesized by hepatocytes and macrophages Normal serum level is 130-300 mg/dl 33
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  Functions of AMG inactivatesall proteases Act as an important in vivo anti-coagulant AMG is the carrier of many growth factors such as platelet derived growth factor (PDGF) Approx. 10 % of the zinc in plasma is transported by α2-macroglobulin and the remainder being transported by albumin Clinical Importance AMG is markedly increased (up to 2-3 g/dl) in Nephrotic syndrome, where other proteins are lost through urine. 34
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  Ceruloplasmin copper containing α2-globulin(Glycoprotein) Single polypeptide chain; 1046 AAs with 3 glycosamine linked oligosachharide side chains. blue in color (Latin, caeruleus= blue). M.W: ≈151,000 Synthesis: mainly by liver where 8 copper atoms are attached to apocaeruloplasmin. & small portion by lymphocytes and macrophages normal plasma half-life is 4-5 days. 35
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  Functions of Ceruloplasmin Ithas enzyme activities of copper oxidase, histaminase and ferrous oxidase. mainly functions as a ferroxidase i.e. helps in oxidation of Fe++ to Fe+++ which can be incorporated into transferrin. 90 % or more of total serum copper is contained in ceruloplasmin and 10% is bound to albumin. carries 0.35 % Cu by weight has eight sites for binding copper [½ as cuprous (Cu+) and ½ as cupric (Cu++)] Copper is bound with albumin loosely, and so easily exchanged with tissues. Hence transport protein for copper is Albumin. Normal conc of serum ceruloplasmin is 25 – 50 mg/dl 36
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  Clinical Importance Increase pregnancy, inflammatoryprocesses, malignancies, oral oestrogen therapy and contraceptive pills. 37 Decrease Wilson’s disease and Menke’s disease. malnutrition, nephrosis, and cirrhosis
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  Wilson's Disease inherited autosomalrecessive condition. defect is a mutation in a gene encoding a copper binding ATPase which links copper to ceruloplasmin and releases it into the bloodstream Clinical features: Accumulation of copper in liver leads to hepatocellular degeneration and cirrhosis. Deposit in brain basal ganglia leads to lenticular degeneration and neurological symptoms. Cu deposition in kidney causes renal damage resulting excretion of amino acids, glucose, peptides and Hb in urine Copper deposits seen as green or golden pigmented ring around cornea; this is called Kayser–Fleischer38
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  Menkes disease Also called“kinky” or “steely” hair disease. It is X-linked disease, so affects only male infants and is usually fatal in infancy. Cause: mutations in the gene for a copper-binding P-type ATPase. intestinal copper uptake by brush border cells is normal, but copper transport to other tissues is affected. This causes reduced activity of numerous copper containing enzymes necessary for structure and function of bone, skin, hair, blood vessels, etc. 39
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  Haptoglobin composed of twokinds of polypeptide chains, two α-chains (possibly three) and only one form of β- chain. These 4 pp chains linked by disulfide bonds. 90,000 dalton Synthesised mainly in liver, very small extent by RE cells Phenotypes: In Human; 3 polymorphic forms Hp1-1, Hp 2-1 and Hp2-2. Functions of Haptoglobin binds free Hb by its α-chain and minimises urinary loss of Hb (Abnormal Hb such as Bart’s-Hb and Hb-H have no α-chains and hence cannot be bound). Hp-Hb complex (155000) cannot pass through glomerular filter  destroyed by RE cells. 40
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  CLINICAL IMPORTANCE normal plasmalevels for adults : 0.3-2.0 g/l Increased plasma levels increased in inflammatory conditions. Protein losing syndromes – compensatory increase DM, Duchenne-type Muscular dystrophy, melanoma Decreased plasma levels Hemolytic disease [Hp levels sensitive marker of in-vivo hemolysis (in mismatched blood transfusion reactions and in HDN)]. Estrogens- decrease in late pregnancy. Newborn period – due to hepatic immaturity 42
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  Β-GLOBULINS Transferrin non-heme iron-containing protein Formerlycalled siderophilin Glycoprotein M.W. : 70,000 Protein part is apotransferrin which can bind two atoms of Fe to form transferrin normal plasma conc. is 1.8 to 2.7 g/l has capacity to bind 3.4 mg of Fe per litre. Normally transferrin is about 33 % saturated with Fe. 43
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  Site of synthesis Principallyby liver. There is also evidence of its synthesis by bone marrow, spleen, lymph nodes and lymphocytes. Functions of Transferrin transport of Fe between intestine and site of synthesis of Hb and other Fe containing proteins. unsaturated transferrin has a bacteriostatic function which is attributed to sequestration of Fe required by microorganisms. 44
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  CLINICAL IMPORTANCE OF TRANFERRIN Increase Iniron deficiency anaemia in last months of pregnancy estrogen administration Decrease In protein calorie malnutrition (PCM), inflammation (negative APR), cirrhosis of the liver, nephrotic syndrome, acute illness such as trauma, myocardial infarction and malignancies. 45
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  C-reactive Protein Conc.: <1mg/dl in the adult male It precipitates with group C polysaccharide of pneumococci, in the presence of Ca++, hence it is named as “C-reactive protein”. Two electrophoretic forms appear on immunoelectrophoresis: • CRP alone in the γ-band, • a CRP complex with an acidic mucopolysaccharide termed m-CRP in the β-region. 46
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  Clinical Significance It canbind to T-lymphocytes, LDL and can activate complement. Can act as an ‘opsonin’ in augmenting immunity indicator of the early phase of an inflammatory process. (Acute phase protein) Plasma levels rises upto 2000 folds after MI, stress, trauma, infection, inflammation, neoplastic proliferation. Plasma levels generally proportional to the degree of tissue damage. Increased hsCRP concn  +ve corelation in predicting the risk of future coronary disease. 47
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  hsCRP Immunologic methods; Nephelometryand EIA measure CRP with sensitivity of approx. 3 – 5 mg/L Recently developed monoclonal antibody-base CRP methods can detect CRP levels below 1.0 mg/L High sensitive or ultra sensitive CRP measured at low levels (1 -10 ng/dl) Marker for risk for atherosclerosis 1. <1.0 mg/L : Low risk 2. 1 – 3 mg/L : Moderate risk 3. >3 mg/L : High risk 4. >10.0 mg/L : Acute phase reaction 48
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  Haemopexin M.W.: 57,000 to80,000 Normal value in adults = 0.5 to 1.0 g/l synthesized by parenchymal cells of liver. Functions to bind and remove circulating haem which is formed in the body from breakdown of Hb, myoglobin or catalase. It binds heme in 1: 1 ratio. The haemhaemopexin complex is removed by the parenchymal cells of liver. 49
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  CLINICAL SIGNIFICANCE OF HAEMOPEXIN Decrease Inhaemolytic disorders At birth in newborns Administration of diphenylhydantoin Increase Pregnant mothers have increased serum levels, In diabetes mellitus muscular dystrophy Some malignancies, especially melanomas. 50
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  Complement C1q Complement isa collective term for several plasma proteins that are precursors for certain active proteins circulating in blood. After the formation of immune complexes, C1q is the first complement factor that is bound. The binding takes place at the ‘Fc’ or constant part of the IgG or IgM molecule. The binding triggers the classical complement pathway. Properties It is thermolabile and is destroyed by heating at 56°C × ½ hour 51
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  The complement systemhelps the body immunity in 4 ways: 1. Complement fixation:  Binds to the foreign invading cells and causes lysis of the cell membrane 2. Opsonization:  Promotes the phagocytosis of foreign cells 3. Inflammatory reaction:  Stimulates local inflammatory reaction and attracts phagocytic cells 4. Clearance of Ag-Ab complexes:  Promotes the clearance of Ag-Ab complexes 52
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  CLINICAL SIGNIFICANCE OF COMPLEMENTC1Q Increase Certain chronic infections In rheumatoid arthritis Decrease In active immune disease such as SLE In protein synthesis disorders Protein losing enteropathy 53 β-Lipoproteins (LDL) Involved in the transport of cholesterol from liver to extrahepatic tissue. Increased: Nephrosis, Hyperlipidemias Decreased: Starvation
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  ACUTE PHASE PROTEINS(OR REACTANTS) Positive APR • C-reactive protein (CRP) • Haptoglobin (Hp) • Ceruloplasmin • α1-antitrypsin • α1-acid glycoprotein (orosomucoid) and • fibrinogen Negative APR Some proteins in inflammatory states decrease; those are called negative acute phase proteins. Eg: Albumin Transthyretin (pre- albumin) Transferrin Retinol binding protein 54
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  Fibrinogen A soluble glycoprotein alsocalled as clotting factor I synthesized in the liver constitutes 4 to 6 % of total proteins of blood Conc. In plasma is 200–400 mg/dL M.W.: 3,50,000 and 4,50,000. Functions as: the precursor to fibrin form bridges between platelets by binding GpIIb/IIIa surface membrane proteins. 55
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  Structure large asymmetrical molecule, highlyelongated made up of 6 polypeptide chains (hexamer): 2Aα, 2Bβ and 2γ-chains thus formula is Aα2Bβ2 γ2. Chains are linked together lengthwise by S-S linkages Being asymmetrical and large, it is important for viscosity of blood. 56
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  On the αand β chains of fibrinogen, there is a small peptide sequence : fibrinopeptide (prevents spontaneously forming polymers with itself) the amino terminal ends of the chains, bear excess of negative charge due to presence of aspartic acids and glutamic acids residues. negative charges  contribute to solubility of fibrinogen in plasma. Clinical significance Congenital fibrinogen deficiency (afibrinogenemia) Hypofibrinogenemia in DIC. 57
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  OTHER PLASMA PROTEINS *Myoglobin: Heme protein found in striated skeletal and cardiac muscles 2% of total muscle protein with Mol wt 17,800 dal (153 a.a) Serum baseline varies with physical activity and muscle mass (30 – 90 ng/ml in adults) In AMI- increase seen within 1 – 3 hrs of onset and reaches peak in 5 – 12 hrs and returns to normal in 18 – 30 hrs 58 * Troponin: Complex of 3 proteins that bind to the thin filaments of striated muscle (not in smooth muscle) 3 complex: troponin T (TnT), troponin I (TnI) & troponin c (TnC) Regulates muscle contraction In AMI- increase seen within 3 – 6 hrs of onset and
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  OTHER PLASMA PROTEINS *Fibronectin: Glycoprotein with activities in cellular interactions including roles in cell adhesion, tissue differentiation, growth and wound healing. Synthesized by the liver hepatocytes, endothelial cells, peritoneal macrophages and fibroblasts Fetal fibronectin is normally present in amniotic fluid and placental tissue Positive test >50 ng/ml indicates a high risk for premature delivery 59
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  CLASSIFICATION 5 main classes (according to M.W and electrophoretic mobility) 60
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  61 Fig: Diagram ofhuman immunoglobulin G (IgG)
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  Ig G (γG) Majorimmunoglobulin making 75% of total Ig 65% of total Ig G is in plasma with 2 heavy chain and 2 light chain with mol wt 150 KDa. 4 subclasses: IgG1, IgG2, IgG3 & IgG4 (differ in hinge region) IgG1 is the principle IgG to cross placenta and protect neonates for the first 3 mths of postnatal life IgD (γD) main function and the role is not yet determined But, IgD along with IgM is the predominant Ig on the surface of human B Lymphocytes it has been suggested that IgD may be involved in the differentiation of B lymphocytes. 62
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  IgM (γ M) 3rdmost common serum Ig. First Ig to produce in response to antigen First Ig produced by neonate Monomeric IgM  membrane bound antibody in plasma  Pentameric IgM IgM (with IgD) is the major Ig expressed on the surface of B cells Polymerisation IgM exists as pentamer with M.W. approx. 900,000 there is a single J-chain in each IgM pentamer. 63
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  IgA (γA) 2nd mostcommon serum Ig. Can be monomer, dimer, trimer or tetramer 2 subclasses:  IgA1 : mostly found in serum; made by bone marrow B cells  IgA2 : mostly found in secretions; made by B cells located in the mucosae Secretory IgA –dimer or tetramer J-chain Secretory component The daily production of IgA is greater than any other immunoglobulin class. 64
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  IgA is foundin external secretions such as colostrum, saliva, tears, GI fluids, prostatic secretion, vaginal secretions, mucous secretions of small intestine, nasal and bronchial secretions. IgA inhibits bacterial colonisation and viral infection of mucosal surfaces. Secretory IgA is slightly different from serum IgA  due to presence of another small protein, called as transport piece (T-Protein or secretory protein or transport protein). 65
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  IgE (γE) Mediates immediate hypersensitivityreaction involved in allergic diseases like hay fever, asthma, etc. bind allergens and triggers the release from mast cell allergic mediators like histamine which is responsible for the characteristic wheal and flare skin reactions IgE defends against worm infections (helminthes) by causing release of enzymes from eosinophils. 66
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  PARAPROTEINS are immunoglobulins producedby a single clone of B cells. on electrophoresisdiscrete band, usually in the γ- region. Plasma electrophoresis  fibrinogen band may mask a paraprotein. Paraproteins (usually IgG or IgA)  most frequently seen in multiple myeloma, solitary plasmacytoma, and in Waldenström’s macroglobulinaemia (IgM). Bence Jones protein in urine are present in about 75% cases of myeloma. In plasma, these Ig light chains of BJP are rapidly cleared. 67
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  Clinical implication ofIg classes 68 Ig class Increase Decrease Ig G Infections of all types Hyperimmunization Liver diseases, Severe malnutrition Rheumatoid arthritis Agammaglobulinemia Lymphoid aplasia, CLL Bence Jones proteinemia IgA myeloma Ig M Waldenström's macroglobulinemia Malaria, Infectious mononucleosis Lupus erythematosus Rheumatoid arthritis Agammaglobulinemia Lymphoid aplasia CLL Ig G and IgA myeloma Ig A Cirrhosis of the liver (most cases) IgA myeloma Agammaglobulinemia Lymphoid aplasia, IgG myeloma, ALL, CLL Ig D Chronic infections, Ig D myeloma, liver disease - Ig E Hay fever, Asthma Agammaglobulinemia
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  69