MODE OF ACTION OF ANTIGEN‐SPECIFIC T‐CELL HELPER FACTORS SECRETED BY A T‐CELL LINE AND CLONES

Abstract

Antigen-specific T-cell helper factors were secreted from a (T,G)-A--L specific T-cell line and clones. The factors were released upon antigenic stimulation and could be induced by a low or a high dose of antigen. The factors secreted upon low-dose stimulation possessed the antigenic specificity of the secreting cells, while the high dose-induced factors had a broader antigenic specificity and could react with the closely related polypeptide (Phe,G)-A--L, even when the cells were restricted to (T,G)-A--L. Both the low dose- as well as the high dose-induced factors could not trigger antibody production in the presence of a non-relevant antigen, and did not collaborate with B cells immunized with a non-related antigen for the production of antibodies. The helper factors, like their secreting cells, were H-2-restricted in the collaboration with B cells. In contrast to the helper cells, however, they did not require accessory cells for triggering the B cells in the process of antibody production. Some preparations of helper factors were found to be inactive. The helper activity could be restored by IL-2. Thus, IL-2 is an additional essential factor required for the antigen-specific collaboration of B cells and T-cell helper factors.