In respiratory and GIT infections, which is the most affected immunoglobulin -

IgA Antibody:- IgA is the second most abundant antibody (2nd highest for DHS). It is of two types: Serum IgA: Predominantly in monomeric form. Secretory IgA (SIgA): It is dimeric (valency four); Secretory IgA is responsible for Mucosal /local immunity. IgA also exist in two subclasses/isotypes: IgA1 is mainly found in serum. IgA2 predominates in secretions. IgA (Secretory IgA) is selectively concentrated in secretions and on mucous surfaces forming an antibody paste and is believed to play, an impoant role in local immunity against respiratory and intestinal pathogens. It protects the mucous membranes against microbial pathogens. It serves an impoant effector function at mucous membrane surfaces, which are the main entry sites for most pathogenic organisms.