Establishment of three PPD-reactive helper T cell clones with distinct functions in B cell activation

Three PPD-reactive long-term cultured helper T cell clones were established from Mycobacterium tuberculosis (Tbc)-primed spleen cells. Clones B11.15 and B12.F were derived from C57BL/6 mice, and clone D-2 was originated from DBA/2Ha mice that have an X-linked recessive inheritance of T cell-replacing factor (TRF) unresponsiveness. Proliferative responses of these cloned T cells were induced by stimulation with PPD in a dose-dependent manner only when I-A-subregion compatible antigen-presenting cells (APC) were present. These three T cell clones have distinct helper functions in B cell activation. Clone B11.15 activated DNP-primed B cells to induce anti-DNP IgM plaque-forming cell (PFC) responses only when high amounts of PPD (5 micrograms) were added to the culture in a major histocompatibility complex (MHC)-unrestricted manner (factor-mediated interaction), whereas stimulation with a low amount of DNP-PPD (0.05 microgram) was ineffective. On the other hand, clone D-2 triggered B cells in the presence of a low amount of DNP-PPD in a MHC-restricted manner (cognate interaction). Significant helper activity of D-2, however, was not observed in the presence of high amounts of PPD. Clone B12.F was able to activate B cells in the presence of either DNP-PPD or PPD. Moreover, both B11.15 and B12.F produced helper factor(s) such as TRF by stimulation with high amounts of PPD in the presence of syngeneic APC, whereas D-2 did not produce measurable helper factor(s) under the same conditions. These results suggest that at least three distinctly functioning PPD-reactive helper T cells can be generated by active immunization with Tbc in vivo. T-B cell interaction between distinctly functioning T cell clones and B cells from (DBA/Ha X C57BL/6) (DB6)F1 male or female mice was then examined. B cells from DB6F1 female mice were triggered by both B11.15 and B12.F in a factor-mediated manner and were also activated with B12.F or D-2 in cognate manner. On the other hand, B cells from DB6F1 male mice, which are TRF low responders, were activated by B12.F or D-2 only through cognate interaction, and they failed to cooperate with B12.F or B11.15 in factor-mediated manner. These findings further suggest that B cells can be triggered by at least two distinct helper T cell subpopulations via respective pathways (cognate interaction and factor-mediated interaction).(ABSTRACT TRUNCATED AT 400 WORDS)