Some biological aspects of lymphocytes reactive to strong histocompatibility alloantigens

Functional interactions of viral and histocompatibility antigens at tumor cell surfaces

Several lines of evidence are presented to suggest that histocompatibility antigens can be physically associated on the cell surface with viral antigens and possibly other foreign antigens. The lysis of the murine tumor cells EL4 and P388 by syngeneic cytotoxic lymphocytes was inhibited by antisera directed against the H-2 antigens on the tumor cells, consistent with the hypothesis that H-2 antigens are part of the target of the cytotoxic lymphocytes. Moreover, it was found that patching and capping of the H-2 antigens on EL4 cells resulted in the co-patching and co-capping of viral antigens as detected by antisera against Rauscher leukemia virus. Capping of H-2 antigens also resulted in co-capping of determinants detected by an antiserum to the viral protein gp69/71. On the basis of these and other observations, we propose the hypothesis that the H-2 molecules serve as adaptors that combine with viral antigens on the cell surface to form hybrid antigens containing elements of self (H-2) and non-self (virus). The adaptor-antigen complex may then be recognized by a subclass of thymus-derived (T) lymphocytes that possesses a repertoire of receptors directed against hybirds of foreign and H-2 antigens. This raises the possibility that other products of the major histocompatibility complex may have analogous functions.

In vitro generation of memory lymphocytes reactive to transplantation antigens

The in vitro generation of memory cells reactive to transplantation antigens is described. Blast cells, obtained from rat lymphocytes sensitized on xenogeneic or allogeneic fibroblast monolayers, reverted to secondary small lymphocytes after transfer from the foreign sensitizing to syngeneic monolayers. These secondary small lymphocytes had a limited in vitro life span of 4-6 wk. They manifested properties of memory cells: upon re-exposure to fibroblasts of the sensitizing phenotype, the secondary lymphocytes adhered to the fibroblast monolayer and transformed into blast cells with cytotoxic activity. The response of secondary lymphocytes was rapid, compared to that of normal lymphocytes, and directed specifically against the primary sensitizing antigens.

Enumeration of activated thymus-derived lymphocytes by the virus plaque assay

Lymphocytes activated by antigens or mitogens acquire the capacity to replicate viruses, and the number of activated lymphocytes can be estimated by the virus plaque assay. Concanavalin A and pokeweed mitogen produced 33-fold and 17-fold increases in virus plaqueforming cells (V-PFC), respectively, above background, while lipopolysaccharide produced only a 2- to 3-fold increase. T (thymus-derived lymphocyte)-depleted lymphocyte populations, derived from anti-theta-treated or nude (arthymic) mouse spleens, failed to produce V-PFC after culture with concanavalin A or pokeweed mitogen. The present studies thus demonstrate that the virus plaque assay measures activated T-lymphocytes.A dissociation between the V-PFC response and cell proliferation was previously observed in antigen-stimulated cells cultured in the presence of mitotic inhibitors. In the present studies, while stimulation of CBA (H2(k)) lymphocytes by DBA/2 (H2(d)) cells produced high levels of thymidine incorporation, lymphocyte target-cell cytotoxicity, and V-PFC, stimulation of BALB/c (H2(d)) lymphocytes against DBA/2 (H2(d)) cells resulted in even higher levels of thymidine incorporation with a virtual absence of cytotoxic lymphocytes or V-PFC. These results indicate that proliferation is not a sufficient condition for permitting lymphocytes either to exert cytotoxicity on target cells or to replicate viruses, and suggest that there may be a correlation between the development of V-PFC and cytotoxic lymphocytes. They are consistent with the view that there are at least two functional subpopulations of T-lymphocytes.