IN-VITRO COMPARISON OF THE BIOLOGIC ACTIVITIES OF MONOCLONAL MONOMERIC IGA, POLYMERIC IGA, AND SECRETORY IGA

Secretory IgA (S-IgA), a major humoral mediator of mucosal immunity, i s a polymeric Ig containing an unusual extra polypeptide, secretory co mponent (SC), added during transcytosis through epithelial cells, Poly meric S-IgA is more effective than monomeric IgA (mIgA) and IgG in neu tralizing viruses, It is not known whether this increased efficacy is due solely to the polymeric structure of the molecule or whether SC it self makes S-IgA more efficient; a quantitative in vitro comparison of the biologic activities of S-IgA and pIgA has not been reported, We p repared purified pIgA and mIgA mAbs directed toward the H1 hemagglutin in of PR8 influenza virus and purified monoclonal S-IgA (made from mon oclonal pIgA injected into a Lewis rat and collected as S-IgA from bil e) and compared their abilities to carry out hemagglutination inhibiti on (HI) and neutralization of the infectivity of PR8 influenza virus i n vitro, The polymeric Igs (pIgA and S-IgA) were 5 times more effectiv e than mIgA in HI and 7 to 10 times more effective than mIgA in virus neutralization, Addition of SC to pIgA did not modify its ability to m ediate HI and had only a minimal effect (S-IgA was 1.4 times more effe ctive) on its ability to neutralize influenza virus in vitro, Trypsin preincubation partially abolished mIgA- or pIgA-mediated, but not S-Ig A-mediated,,viral neutralization, Thus, although S-IgA is more stable functionally than pIgA, the addition of SC does not influence, positiv ely or negatively, the biologic activity associated with the Fab of S- IgA.