Immunoglobulin-dependent helper T cells: studies in the MOPC-315 system suggest a novel surface antigen phenotype.

We have previously provided evidence that the SRBC-immune helper T (TH) cells which enhance MOPC-315 plasmacytoma cell secretory differentiation in vivo (THd cells) differ in specificity, accessory cell requirements, and Qa-1 expression from the SRBC-immune TH cells which enhance MOPC-315 cell growth in vivo (THg cells). Indeed, like other immunoglobulin-dependent TH cells, THd cells in the 315 system do not develop in anti-IgM-treated, B cell-deficient mice, whereas THg cell development is unaffected. In this report, we provide evidence for other differences in the expression of surface antigens by these two TH cell populations. We find that, like most Lyt-1+, 2- T cells, the THg cells can be eliminated by monoclonal anti-L3T4 antibody and complement treatment, whereas such treatment had no effect on adoptive transfer of SRBC-immune THd cell activity. Similarly, THg cell activity was eliminated from SRBC-immune T cells by treatment with monoclonal anti-T cell receptor beta-chain allotope antibody plus anti-rat IgG and complement, whereas THd cell activity remained intact. Both helper cell activities were deleted by either anti-Lyt-1.2 or anti-Thy-1.2 antibody and complement treatment. Interestingly, the THd cell activity was abrogated by treating SRBC-immune T cells with monoclonal anti-B220 or monoclonal anti-p50 antibodies (RA3-3A1/6.1 and RA3-2C2/1, respectively) and complement, whereas THg cell activity was unaffected. Additional controls indicated that the THd effects did not arise by virtue of a two-cell interaction between a Thy-1+, B220- cell and a Thy-1-, B220+ cell, and it is therefore proposed that the THd effect arises from a single population of cells that exhibit a unique phenotype (Thy-1+, Ly-1+, 2-, L3T4-, B220+). The proposal is further supported by studies conducted with a T cell clone which promotes MOPC-315 cell secretory differentiation in vitro and which exhibits this surface antigen phenotype. The serologic differences between these two TH cell populations stress even further the likelihood that B cell growth and differentiation enhancement are mediated by distinct T cell subsets in this system, and raise the possibility that immunoglobulin-dependent TH cells in other systems will routinely exhibit a unique surface antigen profile. These data also imply that immunoglobulin-dependent TH cells (such as the THd cells) may not express antigen receptors that are identical to those expressed by MHC-restricted helper cells (such as our THg cells).