A quantitative assay detecting small numbers of effector helper T cells, regardless of clonal specificity

We have developed a new assay for quantitative detection of all helper T cells that can induce normal B lymphocytes to proliferation and Ig secretion. To establish the optimal assay conditions, we have used cloned T helper cells of defined specificities that had previously been shown to activate normal B lymphocytes expressing the specific antigen(s) on direct cellular interactions. As shown in this paper, 'irrelevant' B lymphocytes--that is, those that do not express either antigen or restriction elements recognized by the effector helper T cells--can also be induced in the presence of appropriate concentrations of pokeweed mitogen which are not mitogenic for the 'target' B lymphocytes. 'Nonspecific' plaque-forming cell responses are of the same magnitude as those provided to specifically triggered targets and equal or better than those induced by lipopolysaccharide. The assay is highly sensitive and enables 'semi-quantitative' detection of less than 20-30 effector T cells per culture. Since effector helper T cells can be detected regardless of the clonal specificity, the assay appears useful for quantitative studies of various populations of T helper cells displaying mixed specificities and for the classification of cells with unknown functions.