Studies on delayed hypersensitivity pleural exudates in guinea pigs. I. Demonstration of substances in the cell-free exudate which cause inhibition of mononuclear cell migration in vitro.

Leucocyte migration inhibitory (MI) activity was investigated in vitro in the delayed hypersensitivity reaction induced by intrapleural injection of PPD into FCA-sensitized guinea-pigs. During the initial reaction (6 h) two types of antigen-dependent MI activity were detected in serum and cell-free exudate. One was of high molecular weight and associated with immunoglobulin and the other was of low molecular weight and appeared to be related to so-called "antigen-dependent MIF". As the reaction progressed (i.e. 12-24 h), two types of antigen-dependent MI activity were revealed in exudate, but not in serum. One was high molecular weight and the other was low molecular weight and thought to be related to so-called "antigen-independent MIF". Similar experiments were performed on the reverse passive Arthus reaction in the pleural cavity of guinea-pigs. A high molecular weight MI activity was detected in 6-h cell-free exudate and was found to be antigen-independent. "So-called MIF" was not found in this reaction.