Immunoglobulins, Cytokines, and Complement system: Immunoglobulins (Ig): Immunoglobulins are Gamma globulins (proteins) of defined specificity for different epitopes that make up antigens. Immunoglobulins are produced by plasma cells. Immunoglobulins are divided into five classes: -Three major classes ( IgG, IgM, IgA). -Two minor classes (IgD and IgE).

N Basic structure of Immunoglobulin: The immunoglobulin molecule consists of four polypeptides : two heavy (H) and two light( L) chains fastened together by disulfide bonds. Heavy chains are designated by using of Greek letters (μ, γ, α, δ, and Є), and the immunoglobulins produced are IgM, IgG, IgA, IgD, and IgE, respectively. Each immunoglobulin isotype carry one type of light chain (kappa and lambda).

n -Heavy chains consist of two different domains ( constant, and variable chains). -Light chains also have two different domains ( constant,and variable). -The flexibility of Ig is associated with the presence of Hinge region ( a Proline-rich region).

Analysis of Immunoglobulin by Enzyme cleavage: -A light chain variable domain and a heavy chain variable domain together form a pocket that constitutes the antigen-binding region (Fab). -Two Fab fragments (Fab) and one Fc fragment are produced by papain cleavage. -Only one fragment ( F(ab) 2 ) is produced by pepsin Cleavage. -Disulfide bonds are reduced by reducing agent (Beta-mercaptoethanol).

n The Enzymatic cleavage of antibody:

Immunoglobulin isotypes: Immunoglobulin G: (IgG): -IgG accounts for approximately 75-85% of the total serum Ig -It is the most abundant antibody produced during secondary humoral immune response. -Monovalent affinity. -Within IgG isotype, the relative concentrations of the four subclasses are: IgG 1 : 60-70% IgG 3 : 4-85% IgG 2 : 14-20% IgG 4 : 2-6% -It is the only class that can cross the placenta.

IgG 1 and IgG 3 structure: n

Immunoglobulin M: IgM: -Found either as a cell-bound monomer or as a secreted pentamer. -Present on B lymphocyte surfaces. -Normally secreted as a J-chain containing pentamer with molecular mass of 900 KD. - Form ~ 5-8 % of normal serum immunoglobulin. - Dominates in early primary immune response. - Anti-A and Anti-B blood groups. - Complement fixation. -Multivalent avidity.

IgM and IgA Structure: n

Immunoglobulin A: IgA: -It accounts for only 10-16% of serum immunoglobulins. -Most abundant in saliva, tears, intestinal mucus, bronchial secretions, milk, prostatic fluid. -The predominant Ig produced in Peyer’s patches (illume submucosa), tonsils and other submucosal lymphoid tissue. (Anti-Viral lysis). -Monomer on B-cell surface (170 KDa). -Dimer when secreted (S.C) (390 KDa). -It has two subclass IgA 1 : IgA 2 in 5:1 ratio in blood.

Immunoglobulin D: IgD: - Has a Molecular weight of 180 KDa. - Present on B-cell surface. - Produced by single alternative splicing of RNA. - Produced against insulin, penicillin, milk proteins and toxoid. - Anti-thyroid-Abs.

Immunoglobulin E: IgE: -Form less than 1% of total serum Ig. -Central involvement in allergic disorders. -Helminthes infection. -Mast cell and Basophils carry a unique high affinity Fc receptor. -Cross-linkage of IgE, immune cell activation, release of Histamine, inflammation.

Molecules of Cellular Interaction: Cytokines: are low-molecular weight soluble protein messengers that are involved in : 1-Cellular interaction ; inflammatory response due to innate and adaptive immunity. 2-Cellular growth and differentiation, and repair mechanism. -Cytokines are produced by a wide variety of immune and non- immune somatic cells. - Cytokines produced by lymphocytes are known as Lymphokines.

N N CytokineCellular SourceTargetsFunction IL-1β Macrophage, B cellT cell, B cell, End.Leukocyte activation End. Adhesion IL-2CD4 cell (TH 1 ) T cell, B cell, NK cell, and Mac. T cell proliferation. IL-4, IL-5CD4 cell (TH 2 ) B cell, T cell, EosDifferentiation of TH 2 and B cell IL-10, IL-13TH 2 *, CD8* cellsB cell, TH 2, Mac.Inhibits IL-2, and INFγ. Down reg. IL-12 TNF-αMac*, PMN, T, B cells. Mac, PMN, T, End.Inflammatory Mediator. TNF-βLymphocytesWide Variety of cells Inflammatory Mediator.

Cytokines and Immune cells interaction: N

N

Interferons (IFNs): Interferons (IFNs) are low molecular weight soluble proteins. -Released by lymphocytes and other somatic Non-immune cells. -Activated by presence of pathogens such as viruses, bacteria, and parasites or tumor cells. -Major Action: 1-Anti-Viral infection. 2-Fight Tumors. Structure of human interferon-alpha

N N InterferonsCellular SourceTargetsFunction INF-α Lymphocytes, Epithelium, fibroblasts. Wide variety of cells. Up-regulates MHC Class I. Inhibit viral proliferation INF-β Epithelium, fibroblasts. Wide variety of cells. Up-regulates MHC Class I. Inhibit viral proliferation INF- γ CD8*, CD4*, and NK cells. T, B, M, NK, End.Anti-Viral. Anti-Parasitic. Enhances MHC Class I and II expression.

The Complement system: Complement system is a series of soluble circulating enzymes and proteins that function in both innate and adaptive immune response against pathogens. The process of complement activation could be initiated via: 1-Alternative pathway. 2-Mannan-binding lectin pathway. 3-Classical pathway.

Alternative pathway: -The initial activation of the alternate pathway is mediated by Properdin factor B binding to C3b. - Properdin factor D splits factor B in the complex yielding the Bb active fragment that remains linked to C3b. -C3 convertase will activate C3b production. -C3b crosslink the complex to produce C5 convertase. -Activation of MAC.

Alternative pathway: N

Classical pathway of Complement activation: -Activation of C1: 1-Ag-Ab enables C1q binding. 2-Activation of serine proteases C1r and C1s. 3-C1qrs complex has enzymatic activity for C2, and C4. -Production of C3 convertase: 1-C4b2b will be produced. 2-C4a, and C2a fragments will be released. -Production of C5 convertase: 1-C4b2b3b complex formation. 2-C5b production, and MAC activation.

Classical pathway of Complement activation: N

The Complement Anaphylotoxins: -C5a, C3a, and C4a fragments. -Acts on: 1-Phagocytes and neutrophils. 2-Endothelial cells. 3-Mast cell. -Action: Inflammatory cascade reactions. Ref. Book page 47.

Mechanism of Inflammation: