Significance of Amount and Avidity of E. coli O Antibodies for Manifestation of their Serological and Protective Properties

Abstract

This preliminary study analyzed the significance of amount and avidity of E. coli·antibodies for serological and protective properties. Using the ammonium sulphate precipitation technique of Farr to measure the primary binding between antigen and antibody and comparing the results with indirect haemagglutination (IHA) it seemed that the latter technique favoured IgM antibodies more and disfavoured IgG antibodies less in serum taken from a primary response, than in serum from an anamnestic immune response. This is possibly due to the increase in avidity of the antibodies seen during immunization. The capacity of antisera to protect mice against an intraperitoneal infection with E. coli bacteria was found to be more closely related to the titres obtained with the Farr technique than to the IHA titres. The relationship of avidity to protection was less clear. The results were consistent, however, with the possibility that low avidity is favourable for the protective function of IgM antibodies in contrast to IgG antibodies for which high avidity seemed important for the protective capacity.