Measurement of antibody-producing capacity in man. I. The normal response to flagellin from Salmonella adelaide.

The immune response to a single subcutaneous injection of 5 μg of flagellin from was examined in 108 human subjects. Titrations were performed by tanned cell haemagglutination before and 1, 2, 6 and 10 weeks after injection. The class of antibody was assessed by mercaptoethanol treatment of serum. Antibody which was entirely IgM was present in 86% of sera before immunization: this is referred to as natural' antibody. After injection of flagellin the response was predominantly IgM, but both IgM and IgG antibody reached peak titres at 2 weeks and both persisted throughout the response. By contrast after a second injection of flagellin the response was almost entirely IgG antibody. The mean titres of total antibody were significantly higher in females than males, and in healthy subjects as compared with those attending hospital for miscellaneous illnesses. There was no significant quantitative difference in the response of subjects grouped according to their titre of natural' antibody, but titres fell more rapidly in the group with a low titre of natural' antibody. Mean titres of natural' antibody were significantly lower in aged than younger subjects, but there was no significant difference in peak titres after immunization. Immunization with flagellin should have considerable potential as a standard test of `antibody-producing capacity' in man, and be applicable to the investigation of immune deficiency diseases and the effects of immunosuppressive agents.