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Human sarcomas, carcinomas and brain tumours were assayed for the presence of immunoglobulins IgG. Among 16 tumours tested, 14 had detectable amount of IgG that could be released when incubated in culture conditions. Addition of iodoacetamide--a metabolic inhibitor--inhibited this " uncoating process ". The uncoated cells rebound IgG if incubated subsequently with any of the cancer sera tested. However, when the autologous serum was present during the uncoating incubation, subsequent rebinding at 4 degree C of IgG from the same or other cancer sera was significantly decreased compared to alquots pre-incubated in other sera.

Sera from repeatedly immunized with allogenic lymphocytes contain IgG that can be fixed by syngenic tumour cells. When compared to the specific anti-H-2 immune response, the paradoxical tumour reactivity is often very high, suggesting an active immunization process. Selective absorptions have demonstrated that the majority of these "anomalous" IgG are directed against membrane components of tumour cells. The nature of the detected tumour-associated determinants is not well elucidated: they are not found on normal embryonnic or adult tissue, but are highly expressed by all in vitro murine malignant cell lines thus far tested, and to a lesser extent by the corresponding in vitro maintained tumours.