RADA-1 cells [H-2a thy-1b; thymus-
leukemia (
TL) 1, 2, 3], a radiation-induced murine
leukemia cell line maintained by serial transfer in histocompatible recipients, resisted lysis by guinea pig
complement (GPC) and
TL 1, 3; TL 2; or
TL 1, 2, 3 antiserum. The cells expressed TL antigenic specificities as determined by indirect fluorescent antibody methods, the direct isolation of
TL antigens from the cells, and the capacity of the cells to reduce known titers of TL
antisera. GPC was consumed to the same extent during the reaction of resistant cells and TL
antisera as occurred in the reaction of sensitive cells (killed under similar conditions) and TL
antisera. RADA-1 cells were not nonspecifically resistant to
complement (C)-mediated lysis; they were killed in the presence of H-2a antiserum and GPC. The TL
antisera contained
antibodies for TL determinants. They stimulated the C-mediated lysis of ASL-1 cells (
TL 1, 2, 3) and thymocytes from strain A mice (
TL 1, 2, 3). The
TL antigens of resistant RADA-1 cells underwent antigenic modulation, the reversible disappearance of
TL antigens from the cells stimulated by specific antiserum. After the cells were treated with
neuraminidase, they became susceptible to the cytotoxic effects of aliquots of the same TL
antisera and GPC used previously.