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Strain difference in immune response of the rat to NRK cells infected with spleen focus-forming virus of the Friend leukaemia virus complex.

Five rat strains were studied for immune responsiveness to SFFV-NRK, a normal rat kidney cell line non-productively infected with spleen focus-forming virus (SFFV) of the Friend leukaemia virus (FLV) complex. Antisera from ACI, JAR, Fischer and SD strains precipitated SFFV-specific gene product, gp55, whereas those from LEW did not. In the cross of Fischer X LEW, immune responsiveness to gp55 was controlled by a single or a few dominant genes. The immune responsiveness was neither related to the susceptibility to FLV infection, nor to the amount of SFFV-related RNA in spleen cells. Unresponsiveness of LEW rats to gp55 was not absolute; when LEW rats were immunized with FLV preparations from infected mice or xenotropic virus-infected NRK cells, they produced antibody that could precipitate gp55.