Subpopulations of splenic T cells regulating an anti-hapten antibody response. II. Distinct functions of, and sequential requirement for, helper and amplifier cells.

In adoptive transfer experiments, two classes of peripheral T lymphocytes, carrier-primed helper (TH) and carrier-primed amplifier (TA) cells, synergized in the induction of a primary anti-hapten IgG response by virgin B cells. Purified TH and TA had separate functions and were required at different times during the antigen-driven development of the response. TH were required early, and provided an initiating signal to B cells in the presence of the specific hapten-carrier conjugate. The differentiative nature of this signal was inferred from the threshold dose-response relationship and the insensitivity of the TH-directed event to the antimitotic agent vinblastine. TA were required 4 days later and provided an amplifying signal to B cells in the presence of the same hapten-carrier conjugate. The proliferative nature of this second signal was inferred from the exponential dose-response relationship and the exquisite sensitivity of the TA-directed event to vinblastine. Virgin B cells became susceptible to the TA signal only after having received the TH signal. TH and TA did not synergize, however, in true secondary responses since hapten-primed B cells depended only on the TH signal to generate large numbers of IgG antibody-forming cells.