Natural killer activity of lymphocytic infiltrates in mouse mammary lesions

Tissue infiltrating lymphocytes were isolated from BALB/c line C4 preneoplastic hyperplastic alveolar nodules (HAN) and spontaneous tumours that arose from the HANs. NK activity of the lymphocytic infiltrates was tested in a 4 h chromium release assay using 51Cr labelled YAC cells. In situ lymphocytes of C4 HAN expressed 3-4 fold greater relative lytic activity (Pross et al., 1981) than did normal spleen cells whereas the relative lytic activity of C4 tumour infiltrates was equivalent or less than that of normal spleen cells. Spleen cells of all lesion bearers had reduced cytolytic capacity. YAC cell lysis by spleen cells and HAN infiltrates correlated with increasing E/T ratios. The degree of YAC lysis by C4 tumour infiltrates, however, either decreased, stayed the same, or increased non-exponentially with increasing E/T ratios especially at E/T greater than 50. Indeed, C4 tumour infiltrates from animals pretreated with anti-asialo GM1 (ASGM) could suppress the NK activity of normal spleen cells. The lytic activity of both C4 HAN and tumour infiltrates could be enhanced or depressed by in vivo treatment with poly IC or anti-ASGM, respectively. These results indicate that NK cells are activated or recruited into C4 preneoplastic lesions but their lytic activity wanes and suppressive activity arises with progression to neoplasia.