Cellular cooperation during in vivo anti-hapten antibody responses. III. The helper cell activity of activated thymocytes, of spleen cells treated with anti-theta serum, and of spleen cells from anti-thymocyte serum-treated or adult thymectomized donors.

An adoptive secondary anti-2,4-dinitrophenyl (DNP) antibody response involving T-B cell collaboration has been studied. In particular, attempts have been made to affect the unexpectedly steep log dose-response curve obtained when graded numbers of helper cells are transferred to irradiated recipients given a fixed number of B cells (premium effect). A variety of means were used to alter helper cell activity, and this activity was then measured quantitatively, as was the ability of the helper cells present after these treatments to give a premium effect. It was shown that activated T cells are approximately twice as active as spleen cells in helper activity and give a comparable premium effect. Graded doses of anti-theta serum plus complement markedly reduce the helper activity of spleen cells without affecting the premium effect given by the residual cells. Treatment of primed cell donors with limited doses of heterologous anti-mouse thymocyte serum (ATS) before transfer does not affect B cell activity, but readily inactivates helper cells, again without affecting the premium effect given by the residual cells. Adult thymectomy (ATx) of helper cell donors before priming with carrier led initially to increased helper activity relative to age-matched control donors. This increase may reflect the loss of nonspecific suppressor T cells from spleens shortly after ATx. Late after ATx, there was about a 2-fold decrease in helper activity, probably reflecting a loss of helper cell precursors. At no time was there any change in the premium effect. In view of the failure of any of the techniques used to abolish the premium effect given by helper cells in this response, it seems likely that this premium effect is due to the cooperative interaction of two very similar types of mature T cell. Alternatively, the premium effect observed here may result from the interaction of two activities of a single type of T cell which is mediated by independent factors.