Delayed hypersensitivity reactions in guinea-pigs using cotton pellets; demonstration of macrophage migration inhibition activity in the cell free exudate.

Subcutaneous implantation of cotton pellets containing PPD into CFA sensitised guinea-pigs produced a reaction of having many characteristics of the delayed hypersensitivity (DH) reaction, together with less conspicuous features of a non-immunological response. The time course of the cellular response in the reaction showed a slow onset, attaining maximum levels between 18 and 24 hr. Mononuclear cells dominated the reaction from 18 to 48 hr. In animals treated with ALS the reaction diminished to the level of a non-immunological reaction. The model made it possible to detect macrophage migration inhibition factor (MIF) activity in the skin exudates. From 6--48 hr high molecular weight antigen-dependent MIF activity was found associated with immunoglobulin. At 18 hr, two types of low molecular weight MIF activity were demonstrated. One was antigen-dependent and the other was antigen-independent. Treatment of sensitised guinea-pigs with ALS abolished the appearance of these factors, suggesting that they might be related to cell-mediated immunity. At 48 hr, the low molecular weight antigen-dependent MIF activity was still evident whereas the low molecular weight antigen-independent activity was not detected. High molecular weight antigen-independent MIF activity was also found at 18 hr. No MIF activity was demonstrated in any of the control exudates.