Inhibition of chicken leukocyte migration in vitro: A direct agarose plate assay

Leukocyte migration inhibition (LMI) is a widely used in vitro correlate of delayed type hypersensitivity (DTH) in mammals. This report describes the development of a direct agarose LMI assay for studying DTH in avian species. Optimum demonstration of LMI was found with leukocytes isolated on a Ficoll-diatrizoate gradient solution. The agarose culture plates were maintained at pH 7.2–7.4 in a water-vapor saturated, 39°C incubator with 2% CO₂ tension.

Antigen specific LMI was demonstrated in chickens with DTH to purified protein derivative of Mycobacterium (PPD) and ferritin. A good comparison between LMI and DTH, as measured by the delayed wattle reaction (DWR), was demonstrated. The effect of bacterial lipopolysaccharide (LPS) on LMI was examined and LPS in microgram quantities was found to inhibit in vitro migration of chicken leukocytes. Contamination of antigen preparations with LPS is a probable explanation for occasional nonspecific inhibition of leukocyte migration since endotoxin is an almost ubiquitous contaminant of antigen preparations.