In vitro response of human lymphocytes to Mycoplasma pneumoniae

In vitro culture and stimulation of human peripheral lymphocytes were employed to investigate the role of cellular immunity in Mycoplasma pneumoniae disease. Subjects with documented natural infections served as donors. The lymphocyte response to whole M. pneumoniae organisms was determined as incorporation of tritiated thymidine in a semimicro culture system. The range of cellular reactivity stimulated by specific antigen was within the range stimulated by phytohemagglutinin. The difference between responses of subjects with documented infection and serologically negative controls was highly significant. Specific reactivity of peripheral lymphocytes correlated closely with the presence of serum growth-inhibiting antibodies, and both persisted for several years following infection. Serum complement-fixing titers correlated well with lymphocyte stimulability during the first year but antibody, as measured by this technique, tended to disappear in later convalescence. In light of previous studies, which revealed a lack of correlation between humoral antibodies and resistance to reinfection, these results suggest that immunity to M. pneumoniae infection is mediated by circulating small lymphocytes.