Significance of the proline assay in the study of anti-MSV cell-mediated immune reactions.

The cytolysis of 3H-proline-labelled tumour cells growing in monolayer by syngeneic immune lymphocytes has been studied in the murine sarcoma virus (MSV) system. Results show that the proline assay (PA) is a convenient way to reveal the activity of cytolytic T lymphocytes against FMR-like antigens. Using the same effector and target cells, the classical chromium-release test (CRT) fails to reveal any cytolytic activity, and the visual microcytotoxicity assay as well as several derived isotopic methods are known to reveal mainly non-specific reactions due to non-T effector cells. The PA, therefore, appears to be a useful method for testing an antitumour reaction against tumour cells in monolayer. The results are, however, different from those obtained in the CRT using the same effector cells but lymphoma cells in suspension as targets, the major discrepancies being the following: (a) the PA does not provide truly quantitative data, due to the very high lymphoid: effector cell ratios needed in this test; (b) unexpected patterns of antigenic specificities are sometimes detected in PA; (c) a non-specific natural killer activity of non-T cells is frequently detected in the PA, masking at low lymphoid: target cell ratios the T-dependent specific cytolysis; (d) the H-2 restriction of the cytolytic T-cell activity is poorly detected in PA, whereas the role of H-2 antigens is clearly shown by blocking experiments using anti-H-2 antibodies.