The expression of theta-like antigen by rat peripheral lymphocytes: serologic and functional studies.

AKR/Cum mice (Thy-1b = thetaC3H) immunized with nucleated cells from WF rat thymus, Peyer's patches, peritoneal exudate, mesenteric lymph nodes, blood, bone marrow, or spleen produced antibodies cytotoxic for ADR/J (Thy-1a = thetaAKR) but not for AKR/Cum thymocytes. The specificity of these antibodies for the Thy-1.1 (theta-AKR) antigen was confirmed by tests using thymocytes from backcross mice segregating at the Thy-1 locus. This result suggested that the rat lymphocyte antgen cross-reactive with Thy-1.1 was expressed by at least some members of each of the rat lymphoid cell populations tested. AKR/Cum mice immunized with killed rat cells also produced anti-Thy-1.1 antibodies; thus indicating that further differentiation of the injected cells was not a prerequisite for the anti-Thy-1.1 response. Unexpectedly, about 9% of unimmunized adult AKR/Cum males were found to be producing antibodies against Thy-1.1. To our knowledge, natural antibodies of this specificity have not been previously reported. Finally, it was found that peritoneal exudate cells taken from WF rats previously immunized with EL-4 mouse leukemia cells were neither killed nor functionally inactivated by treatment with anti-Thy-1.1 antibodies and complement.