1. Dr Nayyer uz Zaman Lecturer Biochemistry KGMC

2.  Antibodies are globulin proteins (Immunoglobulins) that react specifically with the antigen that stimulated their production.  They make up about 20% of the protein in blood plasma  Blood contains three types of globulins: alpha, beta and gamma  Antibodies are gamma globulins

3.  There are five classes of immunoglobulins (Antibodies): ◦ IgG ◦ IgA ◦ IgM ◦ IgE ◦ IgD

4.  Immunoglobulins are glycoproteins made up of LIGHT (L) and HEAVY (H) polypeptide chains  The terms light and heavy refer to the molecular weight  Light chains have a molecular weight of about 25,000 while heavy chains have a molecular weight of 50,000 to 70,000

5.  The simplest immunoglobulin molecule has a “Y” shape and is made up of four polypeptide chains: Two “H” chains and two “L” chains.  The four chains are linked by disulfide bonds  An individual antibody molecule always consists of two identical H chains and two identical L chains

6. Membrane-bound receptor Soluble antibody

7.  L and H chains are sub-divided into “variable” and “constant” regions  The variable regions are responsible for antigen binding  The constant regions are responsible for various biological functions such as complement activation and binding to cell surface receptors

8. Immunoglobulin Structure  Variable(V) & Constant (C) Regions ◦ V L & C L ◦ V H & C H C H1 VLVL CLCL VHVH C H2 C H3 Hinge Region Carbohydrate Disulfide bond

10.  Also known as antibody-mediated immunity  It is directed primarily against ◦ Toxin induced diseases ◦ Infections by encapsulated organisms (eg pneumococcus, Haemophilus etc) ◦ Certain viral infections

11.  THE PRIMARY RESPONSE: ◦ When an antigen is first encountered, the antibodies are detectable in the blood after a long lag period i.e. 7-10 days. ◦ A small clone of B cells or plasma cells specific for the antigen is formed ◦ The first antibodies to form are IgM, followed by IgG or IgA

12.  THE SECONDARY RESPONSE: ◦ When there is a second encounter with the same antigen, months or years after the primary response, there is a RAPID antibody response with HIGHER levels of immunoglobulins (antibodies) and a shorter lag period (only 3-5 days) ◦ There is a much larger amount of IgG made than IgM, although IgM is first to be made in the secondary response. ◦ This is due primarily to the “memory” B-cells that were formed during the primary response. ◦ This is the basis for the concept of vaccination as well

13. IgG  Each IgG molecule consists of two L chains and two H chains linked by disulfide bonds  There are 4 subclasses IgG1 – IgG4 (with IgG1 making up most i.e. approx 65% of total IgG)  IgG is the predominant antibody in the secondary immune response and constitutes and important defense against bacteria and viruses

14.  IgG is the only antibody that can cross the placenta, therefore it is the most abundant antibody in newborns  IgG is one of two antibodies that can activate the complement system (IgM is the other one)  IgG is the immunoglobulin that opsonizes i.e. it can help enhance phagocytosis

15.  IgA is the main immuoglobulin in secretions such as colostrum, saliva, tears and respiratory, intestinal and genital tract secretions  It prevents attachment of micro-organisms e.g. bacteria and viruses to mucous membranes.

16.  IgM is the main immunoglobulin produced in the primary immune response.  It is present as a monomer on the surface of virtually all B-Cells where it functions as an antigen binding receptor.  It is a pentamer  It is the most efficient immunoglobin in agglutination, complement fixation, and other antibody reactions and is important in defense against bacteria and viruses.

17.  It can be produced by the fetus in certain infections  Does not cross the placenta

18.  This immunoglobulin has no known antibody function but may function as an antigen receptor  It is present on the surface of many B- lymphocytes  It is present in small amounts in serum

19.  IgE is medically important for two reasons ◦ It mediates immediate hypersensitivity (anaphylaxis) ◦ It participates in host defenses against certain parasites, e.g. helminths (worms)

20.  IgE (Fc portion) of IgE binds to the surface of mast cells and basophils.  Bound IgE serves as a receptor for antigens (allergen) and this antigen-antibody complex triggers allergic responses of the immediate (anaphylactic) type through the release of mediators e.g. histamine  Although it is present in trace amounts in normal individuals, its levels are raised in persons with allergies

21.  IgE is the main host defense against certain important helminth (worm) infections, such as strongyloides, trichinella, ascaris and the hookworms.  The serum IgE level is usually increased in these infections.  Because worms are too large to be ingested by phagocytosis, they are killed by eosinophils that release worm-destroying enzymes

22.  IgE specific for worm protiens binds to receptors on eosinophils, triggering the antibody-dependent cellular cytotoxicity (ADCC) response.

23. C-reactive protein (CRP)  CRP is a major component of acute phase proteins. It is produced in the liver and is present in the circulation in minute concentration (< 1 mg/dl). C-creative protein (C strands for carbohydrate to which it binds on the capsule of pneumococi) is involved in the promotion of immune system through the activation of complement cascade.  Estimation of CRP in serum is important for the evaluation of acute phase response. In a normal surgery, serum CRP increases and returns to normal level within 7-10 days. If the recovery is complicated by any infection, it will be reflected by the continuous elevation of CRP which requires further treatment.

24.  Multiple myeloma, a plasma cell cancer constitutes about 1% of all cancers affecting the population. Females are more susceptible than mates for this disorder and it usually occurs in the age group 45-60 years.  Abnormal Ig production: Multiple myeloma is due to the malignancy of a single clone of plasma cells in the bone marrow. This results in the overproduction of abnormal immunoglobulins mostly (75%) IgG and in some cases (25%) IgA or IgM IgD type multiple myeloma. In patients of multiple myeloma, the synthesis of normal immunoglobulins is diminished causing depressed immunity. Hence recurrent infections are common in these patients.  Electrophoretic pattern: The plasma of multiple myeloma patients show a characteristic pattern of electrophoresis. There is a sharp and distinct band (M band, for myeloma globulin ) between ß-and γ-globulins. Further, this M band almost replaces the γ-globulin band due to the diminished synthesis of normal γ-globulins.

25.  Bence jones proteins: Henry Bence Jones first described them in 1847. There are the light chains (k or γ) of immunoglobulins that are synthesized in exces. Bence Jones proteins have a molecular weight of 20,000 or 40,000 (for dimer). In about20./. Patients of multiple myloma.  Bence Jones proteins are excreted in urine which often damges the renal tubules.  2. The classical heat test involves the precipitation of Bence Jones proteins when slightly acidified urine is heated to 40-50 0 C. This precipitate redissolves on further heating of urine to boiling point. It reappears again on cooling urine to about 70 0 C.  3. Bradshaw`s test involves layering of urine on concentrated HCL that forms a white ring of precipitate if Bence Jones proteins are present.

26. Thank you