MHC-restricted cytotoxic response of chicken T cells: expression, augmentation, and clonal characterization.

Major histocompatibility complex (MHC)-restricted cytotoxicity of chicken lymphocytes was studied by using three reticuloendotheliosis virus (REV)-transformed cell lines as targets in 51Cr-release assays. The cell lines, designated RECC-UG5, RECC-UG6, and RECC-UG8, were developed from bone marrow cells of REV-infected line G-B1, line G-B2, and (G-B1 X G-B2)F1 chickens respectively. Effector cells were obtained from spleens of G-B1, G-B2, F1, and F2 chickens 7 days after inoculation of REV. The inbred G-B1 (MHC genotype B13/B13) and G-B2 (MHC genotype B6/B6) lines originate from a common partially inbred line. Initial studies with effector cells from G-B1 and G-B2 chickens showed that significant cytotoxicity occurred only with syngeneic target cells. The degree of cytotoxicity was markedly enhanced by neonatally treating effector cell donors with cyclophosphamide (CY) and delaying virus challenge until the birds were 4 wk old. Augmentation of cytotoxicity was presumed to be due to elimination of bursal-dependent suppressor T cells by CY. The results with spleen cells from REV-inoculated F2 birds clearly showed that cytotoxicity was MHC restricted; i.e., significant lysis only occurred if effector cells and target cells had a common B system antigen. Lysis of RECC-UG5 targets was three to four times higher than lysis of RECC-UG6 targets when effector cells were from heterozygous (B6/B13)F1 and F2 birds. Because these two target cell lines generally showed a similar degree of lysis by effector cells from syngeneic B homozygous birds, the differences obtained with effector cells from B heterozygous birds was most likely due to differences in the number of effector cells with specificity for each target line. Evidence for an additive cytotoxic effect, considered to be due to the lytic activity of two separate T cell clones, was obtained when F1 effector cells were tested with the F1-derived RECC-UG8 targets. The results of other experiments indicated that the effector cells were of T cell lineage and that their activity was probably directed against virus-induced antigens on the transformed target cells.