2 Immunoglobulins:Structure and Function Definition: Glycoprotein molecules that are produced by plasma cells in response to an immunogen and which function as antibodiesImmune serumAg adsorbed serum12+-albuminglobulinsMobilityAmount of protein
3 General Functions of Immunoglobulins Ag bindingCan result in protectionValencyEffector functionsFixation of complementBinding to various cellsUsually requires Ag binding
7 Immunoglobulins (Ig) are glycoproteins made up of light (L) andheavy(H) polypeptide chains. Thesimplest antibody molecule has a Yshape and consists of four polypeptidechains:two H chains and two L chains.The four chains are linked by disulfidebonds.
9 Of the five Ig classes or isotypes H chains are distinct for eachOf the five Ig classes or isotypesand are designated γ α μδ ε for the respective classesof Ig, namely IgG IgA IgMIgD IgE.
10 Human Immunoglobulin Classes IgG - Gamma () heavy chainsIgM - Mu () heavy chainsIgA - Alpha () heavy chainsIgD - Delta () heavy chainsIgE - Epsilon () heavy chains
11 Designated κ and λ and only one type is found in Ig. L chains are one of two typesDesignated κ and λ and onlyone type is found in Ig.
12 Human Immunoglobulin Light Chain Types Kappa ()Lambda ()
13 L and H chains are subdivided into variable and constant regions.The regionsare composed of three-dimensionally folded,repeating segments called domains. An Lchain consists of one variable (VL) and oneconstant (CL) domain.Most H chains consistof one variable (VH) and three constant(CH)domains.(IgG and IgA have three CHdomains,whereas IgM and IgE have four.)
15 for antigenbinding ,whereas the constant The various regions are responsiblefor antigenbinding ,whereas the constantregions are responsible for variousbiologic functions eg, complementactivation and binding to cell surfacereceptors.
16 and H chains have three extremely variable (“hypervariable”) amino The variable regions of both Land H chains have three extremelyvariable (“hypervariable”) aminoacid sequence at the amino-terminal end that form the antigen-binding site.
23 IgGStructureMonomer (7S)IgG1, IgG2 and IgG4IgG3
24 IgG Structure Properties Major serum Ig Major Ig in extravascular spacesThe only antibody to cross the placentalFixes complementBinds to Fc receptorsPhagocytes - opsonizationNK cells – ADCCBinds to SPA
25 IgM Structure Pentamer (19S) composed H2L2 units plus one molecule ofJ chainExtra domain (CH4)C4J Chain
26 Fixation of C1 by IgG and IgM Abs C1rC1sC1qNo activationActivation
27 IgM Structure Properties 3rd highest serum Ig First Ig made by fetus and B cellsProduced early in the primary responseThe most efficient IgFixes complementTail PieceAgglutinating IgBinds to Fc receptorsB cell surface Ig
29 IgA Structure Serum - monomer Secretions (sIgA) Dimer (11S), sIgA molecule consists of two H2L2 units plus one molecule each of J chain and secretory component(SC or SP)J ChainSecretory Piece
30 Origin of sIgA: The SP is a polypeptide synthesized by epithelial cells that provides for IgA passage to the mucosal surface. It also protests IgA from being degraded in the intestinal tract.YYY
31 IgA Properties 2nd highest serum Ig Major secretory Ig ( saliva, tears, respiratory, intestinal, and genitaltract secretions.)Does not fix complement unless aggregatedBinds to Fc receptors on some cells