Major histocompatibility complex class II antigen expression on leucocyte subpopulations in the draining lymph node and tumour in the early phase of bacillus-Calmette-Guérin-induced tumour regression.

We investigated the cellular composition and the major histocompatibility complex (MHC) class II antigen expression in the draining lymph node and the tumour during potentiation of the immune response by intralesional bacillus Calmette-Guérin (BCG) administration in the line 10 hepatocellular carcinoma in the strain 2 guinea-pig. Five days after its injection BCG induced a ninefold increase in the number of draining lymph node cells and an increased MHC class II expression. This increased MHC class II expression was mostly due to the selective increase of B cells in the lymph nodes, and to a lesser extent to the increase of T cells expressing MHC class II antigens. Taking into account this nine-fold increase, intralesional treatment of BCG increased considerably the number of T helper/inducer (anti-CT7) and T suppressor/cytotoxic (anti-CT6) lymph node cells expressing MHC class II antigen. The percentage of tumour-infiltrating T cells expressing MHC class II antigen in the tumour was higher than the percentage of T cells in the regional draining lymph node of non-treated guinea-pigs, indicating the presence of activated T cells in the tumour. After treatment with BCG no further increase in MHC class II expression was measured in the tumour, nor was any phenotypical change of the tumour-infiltrating T cells found. In conclusion, with the use of two-colour flow cytofluorometry we have shown that the potentiation of the already existing immune response to line 10 is accompanied by a considerable increase in T helper/inducer, T suppressor/cytotoxic cells and MHC class II antigen in the regional lymph node. Whether this is essential for the potentiation of the immune response causing tumour regression and long-lasting immunity is a subject for further study.