Specificity of the macrophage spreading test with reference to Leishmania antigens and correlation with delayed hypersensitivity.

The inhibition of the macrophage spreading test, claimed to be an in vitro correlate of delayed hypersensitivity, was examined in guinea-pigs immunized with L. enriettii and L. tropica soluble antigens. Cells from peritoneal washings of the guinea-pigs were tested in presence of the homologous and heterologous antigens and also without antigen. Inhibition of macrophage spreading compared to control preparations was noted only in the presence of the homologous antigen when the skin test response of the donor animal was relatively small. The degree of inhibition decreased as the skin test volume increased and when skin test volumes were large there was actual stimulation of macrophage spreading, rather than inhibition. The addition of heterologous antigen to the peritoneal cell preparation always resulted in the augmentation of macrophage spreading above control levels. The possible mechanisms of this in vitro technique and its use as a taxonomic or diagnostic tool are discussed.