Immunology

1. Immunology
By
Ahmed Riyadh Abdul Rahman
Al-Noor University College
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2. 2. Immunoglobulin M (IgM)
 IgM represent about (10- 15%) of the total normal serum Ig content.
 IgM takes one of two forms:
1.A pentameric structure (In the serum, Serum IgM) consisting of five monomer units
linked together by disulfide bonds at the Fc fragment of the μ chains, and a single
short J chain, to held all the monomers together. Each of the five monomers is
composed of two light chains and two heavy chains, with the additional constant
domain replacing the hinge region.
2.A monomeric structure (found on B lymphocytes
as B cell receptors).
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3.  IgM molecular weight about~900 kDa, Because of its large size, IgM is found
primarily in the intravascular space (i.e. in the bloodstream and lymph fluid).
 Sedimentation coefficient of IgM is (19s), the largest Ig molecule.
 IgM has a half-life of approximately 5-7 days.
 IgM is the first antibody produced of primary immune response.
 IgM is the predominant antibody in the early (primary) immune response to most
antigens.
 It is responsible for agglutination, viral & toxin neutralization and cytolytic
reactions (Antibacterial, antiviral and antitoxin activity) and it is important in
complement activation and agglutination reactions to combat pathogens.
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4.  IgM is the most efficient immunoglobulin at activating complement the classical
pathway in lytic reactions.
 IgM antibodies usually very efficient per molecule in dealing with pathogens
especially early in the immune response comparing with IgG, because IgM is
pentameric (have ten antigen binding sites).
 IgM can't cross the placenta.
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3. Immunoglobulin A (IgA)
 IgA represents 15- 20% of the total circulatory Ig content.
 Immunoglobulin A (IgA) exists as a monomer, dimer. Dimeric forms of IgA are consist of two
monomer associated with a J chain and secretory component (SC).
 IgA Sedimentation coefficient could be 9S, 11S, or 13S.
 IgA molecular weight about~160 kDa.
 IgA has a half-life of approximately one week.
 In humans, IgA has two subclasses (IgA1and IgA2).
 IgA (serum IgA) is found in small amounts in blood (intravascular).
 IgA (secretory IgA) is found predominantly in the gastrointestinal tract and in secretions such as
tears, sweat, and saliva, mucosal secretions (extravascular). IgA is present at all external surfaces
(except skin). IgA is also the major antibody of milk and colostrum. Consequently, infants who
are breastfed are acquires the mother’s immunity to gastrointestinal pathogens.

6.  IgA bind to glycoprotein called the secretary piece; it protects IgA from digestion by
gastrointestinal proteolytic enzymes and forms a complex molecule named secretary IgA.
Secretary IgA is important in protecting body surfaces against invading microorganisms.
 Secretory IgA provides local immunity protects mucous membranes and secretion of
respiratory, digestive, and urogenital system.
 IgA has pathogen neutralizing function (IgA neutralize viruses and prevent attachment on host
surface).
 IgA do not activate complement only aggregated IgA activates the alternative pathway of
complement.
 IgA unable to cross the placental barrier.
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7. 4. Immunoglobulin D (IgD)
 Immunoglobulin D (IgD) is a unique immunoglobulin with a low concentration in
serum and the exact function of which is not known.
 IgD represents about 0.25% of the total serum immunoglobulins.
 IgD has a monomeric structure and has a relative M.W of 180 kDa.
 Has a half-life of about 3 days.
 Has a sedimentation coefficient of approximately 7S.
 (IgD) exists on naive B cells surface, along with IgM.
 The co-expression is found on the surface of majority of B cells. IgD starts to be
expressed when the B cell exits the bone marrow to populate peripheral lymphoid
tissues. When a B cell reaches its mature state, it co-expresses both IgM and IgD, so,
it play role in B-cell maturation.
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8.  IgD is also produced in a secreted form that is found in very small amounts in blood
serum.(ex: in the case of myeloma)
 The function(s) of IgD remain under investigation.
 IgD don't cross the placenta.
 Dose not binds complement.
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5. Immunoglobulin E (IgE)
 Immunoglobulin E (IgE) is a monomeric antibody, normally barely detectable in
serum because most IgE is bound to FcεR on mast cells and basophils.
 IgE has a molecular weight about180-200 kDa.
 Has a sedimentation coefficient of approximately 7S-8S
 It has a half-life of about 2 days in serum.
 The normal level of IgE is 500ng/ml, but its level increases hundreds or thousands of
times in cases of allergy (immediate hypersensitivity) reactions and in parasitic
infections, specifically helminthes in the gastrointestinal tract and in anaphylaxis
cases.
• IgE binds to basophils and mast cells and eosinophils by Fc receptor.

10.  The function of IgE include:
1. Allergic reactions occur when IgE on mast cells are cross-linked by binding to the
same antigen (allergen), the mast cells degranulate. Degranulation releases mediators
of inflammation (e.g., histamine, heparin serotonin, slow reacting substance of
anaphylaxis SRSA, cytokine and other inflammatory mediator) which involved in
vasodilation which lead to immediate hypersensitivity syndromes (such as hay fever
and asthma such as allergic asthma, sinusitis, allergic rhinitis, food allergies, and
specific types of chronic urticaria and atopic dermatitis). It also stimulates production
of an excessive number of eosinophils in the blood (eosinophilia) and increased rate of
movement of the intestinal contents (gut hypermotility), which aid in the elimination of
helminthic parasites. Thus although IgE is present in small amounts, this class of
antibodies has potent biological capabilities.
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2. IgE provide immunity to parasites such as helminthes.
3. IgE linked to the anaphylaxis which plays role in responses to allergens, such
as: anaphylactic drugs, bee stings.
 Estimation of Total IgE is very important because Increased IgE serum levels give a
sign of allergic reaction, hypersensitivity, anaphylaxis, and parasitic diseases. And it
should include the Estimation of specific IgE to specific allergen (specific allergen-
IgE complex)
 IgE Does not fix complement.
 IgE don't cross the placenta.

13. ***Link the correct answers:
a. IgG
b. IgE
c. IgM
d. IgA
e. IgD
1. crosses the placenta
2. has the longest half life
3. is present in the highest concentration in circulation
4. has a J region
5. expressed on immature B cells
6. in aggregated form activates the alternative pathway of complement
7. bound to FcεR on mast cells and basophils
8. most efficient ( when bound to antigen) at activating the classical pathway of
complement
9. is known as the reaginic antibody
10. transferred to the infant during breast feeding
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