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Hooded Lister/Cbi rats bearing the HSN.TC fibrosarcoma produced a high-titre non-complement-binding IgG antibody, and tests in vitro indicated that the syngeneic antibody was specific for this tumour. About 1.4 X 10(5) antibody molecules were bound per cell, a figure one eighth that for cells treated with a high-titre allo-antiserum. When tumour-bearer serum was passively transferred into congenitally athymic rats bearing the HSN.TC tumour the antibody was absorbed out specifically, by comparison with control animals or athymic rats bearing an unrelated tumour that was also syngeneic in Hooded rats. The kinetics of loss of antibody from the surface of HSN.TC cells has been monitored in vitro and the antibody has been found to have an extended half-life at the cell surface (greater than 40 h).

The importance of host immune status on the spontaneous metastasis of cloned cell lines of the 13762NF rat mammary adenocarcinoma was examined. Cell lines MTLn3 (high metastatic potential), MTF7 and MTLn2 (intermediate metastatic potential) and MTC (low metastatic potential) were subjected to a series of in vivo assays designed to assess how manipulation of the immune system in the syngeneic F344 host would affect the ability of these cells to metastasise. Treatment of tumour bearing rats with the immunosuppressive agents cyclosporin A or cyclophosphamide had little influence on metastasis in this system. Growth of tumours in congenitally athymic nude rats resulted in reduction of observed metastases. In addition, humoral immune response was not detectable during a 23-day period of tumour growth in F344 rats. Excision of the tumour growing in situ reduced the number of metastases when the tumours were resected early (less than 10 days), but at later times tumour resection did not influence the incidence of metastasis. The importance of initial lymphatic rather than haematogenous routes of dissemination was confirmed in experiments where the draining inguinal and axillary lymph nodes were removed at different times either before, or after, subcutaneous mammary fat pad injection of metastatic tumour cells.