1. Dr Shoaib Raza

2.   B lymphocytes are also called as B-Cells  Develop in the yolk sac  Migrate to bone marrow  Processing, differentiation and maturation take place in  Bursa of fabricius or its equivalent organ  Reside in the lymphoid follicle B- Cells

3.   B-Cells recognize freely circulating antigens, that are soluble  B-Cells are provided with BARC (B-Cell Antigen Receptor Complex)  IgM is an important constituent of BARC  IgM present on surface occurs as monomer (different from circulatory IgM) B-Cells & Antigens

4.   Upon antigenic stimulation under influence of cytokines released from T- Cells:  Antigen is perceived by sIgM  Antigen-antibody complex is internalized  Primary antibody is formed  Usually IgG (Primary response)  Differentiation leads to formation of IgM by plasma cells B-Cells & Antigens

5.   Meanwhile B-cells undergo transformational changes to form plasma cells  More cytoplasm  Eccentric nucleus  Amphophilic cytoplasm owing to increased number of RNA and Golgi apparatus  A perinuclear halo is characteristic of plasma cells  Plasma cells are formed within germinal center of lymphoid follicle  Cytokines and growth factors are released from macrophages B-Cells & Antigens

6.   Is an immunoglobulin  Formed by plasma cells (activated B-Cells) in response to antigenic stimulation  Is a protein  Made up of two light and two heavy chains  Binds with antigen result in:  Neutralization  Agglutination  Precipitation, etc. Antibody

8.   Composed of four chains of polypeptide  Joined together by disulphide linkages  Hinge region  Two fragments  Fab fragment  Binds with antigen  Fc fragment  Performs certain cellular functions  Binds to cell receptors  Complement activation  others Structure of Antibody

9.   Four chains are  Two heavy chains (alpha, gamma, mu, delta, epsilon)  Two light chains (kappa and lambda)  Each heavy chain composed of four domains  Three constant domains (CH) & one variable domain (VH)  Each light chain composed of one constant, and one variable domain  The variable domains of both the light and heavy chains contain a hypervariable segment (site for binding with antigen)  It varies in various antibodies  An antibody molecule can bind with two molecules of antigen Structure of Antibody

13.   Five classes of Antibody  IgGGamma γ heavy chain  IgAAlpha α heavy chain  IgMMu μ heavy chain  IgDDelta δ heavy chain  IgEEpsilon ε heavy chain Classes of Antibody

14.   Isotypes:  Are defined by antigenic differences in their constant regions  IgG, IgM, IgA, IgD, IgE  Allotypes:  Are additional antigenic features that vary among individuals  Idiotypes:  Antigenic determinants formed by specific amino acids in the hypervariable region Isotype, Allotype, Idiotype

15.   Two Gamma heavy chains, two kappa or lambda light chains  Secondary response  Present as monomer (Bivalent)  Opsonization via its Fc portion  Complement activation via classic pathway  May cause agglutination  Four subtypes  IgG 1  IgG 2  IgG 3  IgG 4 IgG

16.   Two mu heavy and two kappa or lambda light chains  Occur in two forms  Pentamer in circulation (decavalent)  Monomer on surface of B-Cells as part of BARC  Important functions are:  Agglutination  Reception of antigen by B-Cells  Primary response  Activate complement via alternate pathway IgM

18.   Two alpha heavy, two kappa or lambda light chains  Usually present in secretions (secretory antibody)  Present as dimer (tetravalent)  Two antibody molecules are joined together by a J- chain (joining chain) IgA

20.   Two delta heavy, two kappa or lambda light chains  Occurs as monomer  Traceable amounts in plasma  No known biological function  May be part of BARC IgD

21.   Two epsilon heavy, two kappa or lambda light chains  Present in trace amounts in normal individuals  Levels are higher in atopic person  Binds to allergen by Fab fragment  Binds to mast cells through their Fc portion  Induces Type I Hypersensitivity reactions (Allergic reactions e.g. allergic asthma) IgE

22.   Induction of humoral immunity via antibody synthesis from plasma cells  Agglutination, neutralization, precipitation, complement activation, opsonization, etc  B-Cells are provided with both MHC I & II molecules, therefore are one of the most potent antigen presenting cells to T-Cells, after macrophages Functions of B-Cells

23.   Assignment to be completed Differences between B- Cells & T-Cells

24.  MHC

25.  MHC-II