Heterogeneous Expression of Antigenic Determinants by Rat Lymphocytes

Abstract

Summary. 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 (PVGxF,) 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.

The Relationship of the Antigenic Determinants Expressed by Rat Lymphoid Cells to Their Participation in Graft‐versus‐host Reactions

“…Cytotoxicity of antisera was assayed in a one-stage test as outlined by McCullagh (1985). Net susceptibility of lymphocytes to alloantiserum and complement as measured with TVypan blue was calculated as:…”

“…Nevertheless, the occurrenee of uniform IPSA susceptibility in lymphocytes from many backcross and F2 hybrid rats remains consistent with the existence of variable levels of expression of MHS determinants by the cells of a population. As indicated when considering the uniform effects of IPSA on cells from parental strain and Fj hybrid rats (McCullagh, 1985), 100% killing of a cell population could be quite effectively achieved by an antiserum possessing a number of activities, the target determinant for at least one of which was carried by any cell in the population. Additional cytotoxic effects directed against non-MHS determinants cannot be excluded and could have resulted in augmentation of estimates of suseeptibility of some populations.…”

“…The preceding paper (McCullagh, 1985) reported that lymphocytes from F2 hybrid and backcross rats of the inbred PVG and DA strains displayed unexpected patterns of susceptibility to inter-parental strain alloantisera (IPSA). It was concluded that the most likely explanation for this was variation in the level of expression of target antigens.…”