<prompt> Ig seen in breast milk secretions:IgAIgEIgGIgD  <response>: Ans: a IgA Ref: Ananthanarayan, 7th ed, p. 88, 89Serum IgA is the major Ig in colostrums, saliva tears.It is concentrated in secretions and on mucus surfaces forming an antibody paste.It is important in immunity against respiratory intestinal pathogens.Properties of Immunoglobulins:IgMIgG Maximum intravascular concentration Maximum molecular weight Maximum sedimentation co efficient Earliest Ig by the foetus Increased in primary immune response Activate classical pathway Mediates hypersensitivity pneumonitis Maximum serum concentration Longest half life 23 days Only Ig to cross placenta Ig to increase in secondary immune response Fixes complement by classical pathway except IgG4 IgAigE Secreted by seromucinous glands Ig present in milk. Other one is IgG Fix complement by Alternate Pathway Mediator of type 1 HS Only heat labile Ig Shortest half life 2 days, least amount in serum Maximum carbohydrate concentration Shows homocytotropism Mediate Prausnitz Kustner reaction. Igs activating alternate pathway - IgG4, IgA, IgD IgG in multiple myeloma, IgM in Waldenstroms macroglobulinemia Ig dimer is IgA. Ig pentamer is IgM 