Heterogeneous expression of antigenic determinants by rat lymphocytes.

Exposure of lymphocytes from F2 hybrid and backcross rats of the PVG and DA strains to inter-parental strain alloantisera and complement frequently and unexpectedly revealed incomplete susceptibility within a population of cells. This heterogeneity did not appear to result from variable susceptibility to cytotoxic mechanisms. A more likely explanation was that variation occurred in the expression of the target determinants within the lymphocyte population. A similar heterogeneity was also demonstrable in populations of lymphocytes from rats of the inbred DA strain, provided appropriate alloantisera were used. Antisera raised in PVG rats against individual (PVG X F1) backcross rats frequently effected intermediate levels of DA cell destruction in the presence of complement, although exposure of DA lymphocytes to PVG anti-DA serum plus complement resulted in their uniform destruction. The nature of the target antigens that were subject to variable expression was not established, but it seemed likely that they were related to histocompatibility determinants.