Evidence of direct recognition subset in xeno-reactive helper T cells

There are two functional subsets of alloreactive helper T cells: one recognizes the alloantigens on self-antigen-presenting cells (APCs), and the other recognizes the alloantigens on allo-APCs. In this study, we analyzed which specific Th cells have a possible effect on concordant-xenograft rejection responses and how Th cells recognize xeno-antigens. In the proliferative response stimulated with spleen cells obtained from rats (r-SPC), mouse T cells (m-Tc) were not inhibited by GK1.5 (CD4) or 2.43 (CD8) antibodies. In a xeno-mixed lymphocyte reaction, m-Tc that included APC (APC(+)) proliferated when stimulated with r-SPC APC(+) or APC(-). In contrast, B6 T cell APC(-) proliferated only when stimulated with r-APC(+)SPC but not when stimulated with APC(-). The m-Tc lines responded to F344 SPC APC(+) but not to SPC APC(-); however, the m-Tc line did not respond to SPC from another rat strain. We hypothesize that both CD4+ Th and CD8+ Th are included in the concordant xeno-reactive Th; there are both xeno-APC-restricted Th and self-APC-restricted Th; and xeno-APC-restricted Th recognizes xeno-major histocompatibility complexes.