Proportion of protein A bindable molecules in human IgM and IgA antibodies to seven antigens

Human IgM or IgA antibodies to seven antigens (tetanus and diphtheria toxoids, and five bacterial polysaccharides) were studied by determining what proportion of these antibodies were bound by staphylococcal protein A. This alternative binding is a marker of V_H genes of family 3. Each response was studied in an average of nine individuals. The binding proportion of antibodies to the two toxoids resembled that of total serum immunoglobulins; 13-14% of IgA and 40% of IgM antibodies were bound by protein A. All anti-polysaccharide antibodies had higher proportions of protein A bindable molecules than serum IgM or IgA indicating a bias for V_H genes. This excess was high in antibodies to Haemophilus influenzae type b (Hib) and pneumococcal type 14 polysaccharides (>two-fold). It was moderate but statistically significant in antibodies to pneumococcal types 18C and 3 capsular polysaccharides and to C polysaccharide. All vaccinated Finns exhibited the V_H3-preference in antibodies to Hib and type 14 polysaccharide.