Relation between low capacity of human sera to inhibit streptococcal mitogens and serious manifestation of disease.

The proliferative response of lymphocytes induced by a new streptococcal mitogenic factor (MF) and the streptococcal pyrogenic exotoxins (Spe) A and B was determined in sera from 6 healthy persons. Responses were compared to those obtained from reference serum that lacked mitogen-specific ELISA antibodies. The sera showed individual variations in the levels of MF- and Spe-specific antibodies, as determined by ELISA. The experiments showed that most human sera, which contained mitogen-specific antibodies, could neutralize the mitogenicity of the proteins. However, there were sera that contained mitogen-specific antibodies but that did not inhibit the toxin-induced proliferation. Thus, the ELISA antibody titer did not always equal the neutralizing capacity. Sera from 27 patients with group A streptococcal bacteremia had significantly lower neutralizing ability against MF and SpeB than did sera from 25 uncomplicated tonsillitis cases.