Historical background and aspects of the mechanism of leukocyte adherence inhibition.

The development of leukocyte adherence inhibition is traced from early experiments with murine tumors to recent applications in human cancer and in cell-mediated immunity in general. Arbitrary experimental conditions (serum in culture medium, preincubation, and tumor extracts at a single concentration) were initially set up and permitted detection of specific inhibition of adherence of sensitized leukocytes reacting with antigen of the tumor extracts. Blocking serum completely or partially restored adherence. It was readily demonstrated that leukocyte adherence inhibition was mediated by a soluble lymphokine-like factor [leukocyte adherence inhibition factor (LAIF)]. Recent studies suggest that serum is important in enabling detection of LAIF; this may explain the inability of some other workers to confirm our findings. Serum appears to protect LAIF from enzymatic destruction in mixtures containing tumor extracts. Complex cell interactions are involved in LAIF production. With mouse cells in vitro, macrophages are required for production by both T- and B-lymphocytes, and there is evidence for suppressor cells also.