In vivo functional clonal deletion of recipient CD4 super(+) T helper precursor cells that can recognize class II MHC on injected donor lymphoid cells

Intravenous injection of semiallogeneic (C57BL/6XDBA/2)F sub(1) lymphocytes into adult C57BL/6 recipient mice not only, as previously reported, reduces the recipients' cytotoxic T lymphocyte response in a subsequent in vitro mixed lymphocyte reaction against the injected cell type, but also reduces Th cell function in the same MLR. Thus lymphoid cells derived from the injected mice were greatly reduced in their ability to proliferate and to produce IL-2 in response to (C57BL/6XDBA/2)F sub(1) stimulator cells in vitro, whereas third party responses were unaffected. This appears to be due to a reduction in the precursor frequency of IL-2-producing T lymphocytes specific for the injected cells as measured by limiting dilution analysis. Our data shows that class II-specific Th responses are similarly reduced in the injected mice and suggest that CD4 super(+) class II-reactive precursors of Th cells may be functionally inactivated in vivo by donor cells via a veto-like mechanism.