We sought to examine the role of immune response (Ir) genes in helper T cells. To eliminate allogeneic effects, we used neonatally tolerized mice. The results bear not only on the mechanism of Ir genes, but also on the development of the T cell repertoire. B 10.BR (H-2(k)) or C57BL/10 (H-2(b)) mice, which were low responders to myoglobin (Mb), were neonatally tolerized to high responder H-2(d) alloantigens, and B10.D2 mice, which were high responders to Mb, were neonatally tolerized to low responder H-2(k) or H-2(b) alloantigens. Spleen cells from these tolerized mice did not show any reactivity in mixed-lymphocyte reaction or cell-mediated lympholysis against alloantigens used in tolerization. Mb-immune F(1) B cells were helped comparably by Mb-immune tolerized low or high responder T cells. Thus, low responder T cells functioned equivalently to high responder T cells. The failure of nonimmune T cells from tolerized low responder mice to help F(1) B cells and antigen-presenting cells (APC) indicated that collaboration between B10.BR or C57BL/10 T cells and F(1) B cells was not caused by a positive allogeneic effect. Spleen cells from tolerized mice were contaminated with 2-4 percent chimeric F(1) cells, as judged by fluorescence-activated cell sorter analysis, and no F(1) alloantigens were detectable in the thymus. However, removal of chimeric F(1) T cells from the tolerized cell population by treatment with anti-H-2 and complement did not change the helper activity of tolerized low responder T cells. These data indicated that helper activity in the T cell population from low responder mice was not due to F(1) cells. Also, the level of contamination was not sufficient to quantitatively account for the help. In examining the genetic restriction of these tolerized T cells, we found that T cells from tolerized low responder B10.BR or C57BL/10 mice helped F(1) or high responder B10.D2 B cells and APC but not syngeneic B10.BR or C57BL/10 B cells and APC, which were immunized with Mb-coupled fowl gamma globulin instead of Mb to prime low responder B cells with Mb. On the other hand, high responder B 10.D2 tolerized T cells helped syngeneic B 10.D2 B cells but not allogeneic low responder B10.BR B cells.

These data indicated that clones of helper T cells specific for Mb exist in low responder mice, and these are not phenotypically different from those in high responder mice, in that both help high responder and F(1) but not low responder B cells and APC. These data are discussed in terms of the mechanism for Ir gene control, and the mechanism of T cell repertoire development- whether intra- or extrathymically-in neonatally tolerized mice.

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