Leukocyte adherence inhibition: A simple test for cell‐mediated tumour immunity and serum blocking factors

A proportion of peritoneal leukocytes from CBA mice adhered to glass haemacytometer surfaces and withstood a gentle washing. This proportion was reduced with cells taken from mice sensitized to a methylcholanthrene‐induced tumour, when the specific tumour antigen was added in the form of a soluble extract. The reaction of leukocyte adherence inhibition (LAI) may have an immunological basis similar to that of macrophage migration inhibition, but LAI is a much simpler procedure. Leukocytes were active in LAI when taken from animals bearing tumours and after tumour removal. When serum from mice bearing a particular tumour was added to sensitized leukocytes in the presence of the specific tumour antigen, the inhibition of adherence was substantially relieved or blocked. LAI could thus be used to demonstrate both cellmediated immunity to tumours and blocking factors in serum by a brief, simple procedure. A potential application to human tumour immunology is indicated.