THE ABILITY OF IgA TO INHIBIT COMPLEMENT CONSUMPTION BY COMPLEMENT‐FIXING ANTIGENS AND ANTIGEN‐ANTIBODY COMPLEXES

Abstract
The polymeric and monomeric (7S) forms of the nitrophenyl-specific MOPC-315 murine IgA myeloma protein were examined for their capacity to inhibit the consumption of guinea-pig complement (C) by the C-activating protein DNP46BSA and by antigen-antibody (Ag-Ab) complexes. On a molar basis. 13S IgA was slightly (2–3 fold) more efficient than 7S IgA in inhibiting C consumption by DNP-BSA. When mixed with IgG antibodies prior to incubation with a non-complement-fixing antigen (TNP-KLH). 13S IgA was considerably more effective than 7S IgA in preventing the formation of Ag-Ab complexes able to fix C. The degree of inhibition observed was related to the concentration of C used in the assay, being greater at lower C concentrations.

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