The role of T cells in regulating immunoglobulin class and subclass.

A plaque-forming cell assay was used to follow the changes in Ig class and subclass during the response of mice to repeated injections of sheep red cells. The proportion of IgG1 rose, and that of IgG2b fell, as the response proceeded. In cell-transfer experiments both B and T cells displayed this tendency, and when asynchronously primed cells co-operated together, the pattern was characteristic of the longer-primed population. Thus T cells can advance, but cannot reverse, the progress of isotype changes in B cells. Evidence is presented for two physically separable T-cell subpopulations which need to interact in order the help B cells produce certain isotypes.