CELLULAR IMMUNOLOGY 20, 229-240 (1975) Studies of the Mixed Lymphocyte Reaction by the Virus Plaque Assay1

The virus plaque assay has been developed as a tool for enumerating activated lymphocytes. In previous studies using mitogens it was found that the assay detects activated Tbut not activated B-lymphocytes. In the present studies, the mixed lymphocyte reaction was studied by the virus plaque assay as well as by incorporation of thymidine and development of cytotoxic lymphocytes. In combinations differing at the entire major histocompatibility complex, approximately 1% of the cells were activated and treatment with anti-thy.1 serum totally abrogated the virus plaque forming cell (V-PFC) response. In studies on the A.TH-A.TL recombinants and the AQR-BlO/ 6R recombinant strains, incompatibility at the H-2-K or H-2-D loci were found not to be capable of activating T-cells to produce virus plaques. In contrast, differences in I or I plus S regions caused a marked T-cell activation, 3-6s of the cells being V-PFC. There was a general parallelism between thymidine incorporation and the V-PFC, and it was not possible to dissociate the cell types carrying out each of these functions by kinetic studies. However, preinfection of responding cells with the virus used in these studies, vesicular stomatitis virus, caused a complete abrogation of thymidine incorporation, indicating that the activation of virus is an earler stage than DNA synthesis, and that viral activation will block further ccl1 replicaton and is probably a lytic event.