Human cell-mediated immunity to tuberculin as assayed by the agarose micro-droplet leukocyte migration inhibition technique: comparison with the capillary tube assay.

Direct and indirect agarose microdroplet migration inhibition assays were performed with log dilutions (50--5 X 10(-8) microgram/ml) of soluble purified protein derivative (PPD) of tuberculin and leukocytes (4 X 10(5)/droplet) from PPD skin test positive or negative individuals. Some tests were run in parallel with the capillary tube method. Inhibition of migration of leukocytes from 9/11 PPD skin test positive donors studied was observed in direct tests when employing PPD doses ranging from 1--50 microgram/ml PPD. Inhibition of migration of leukocytes from some PPD skin reactive donors was obtained with as little as 5 X 10(-3)--5 X 10(-7) microgram/ml (i.e., 5 nanograms to 0.5 picograms). Some inhibition of leukocyte migration was seen with skin test negative donors (presumably toxicity) with the higher doses of PPD (50 microgram/ml), but generally little inhibition was observed with these donors at lower doses. Comparative experimetns of the agarose micromethod and the capillary tube technique indicated that the agarose assay was more sensitive in that it could detect reactivity with 2--4 logs lower antigen concentration. Indirect assays using supernatants of cultures of PPD triggered mononuclear cells and indicator granulocytes in agarose droplets demonstrating that a lymphokine (presumable leukocyte inhibitory factor) was being produced and suggested that cell-mediate immune (CMI) reactions were operative. The results indicate the usefulness of this technique in the sensitive-detection of CMI against such antigens as soluble PPD. The assay should prove useful in quantitative assessment of cell-mediated reactivity by using a wide range of antigen concentrations and the leukocytes from as little as 2--5 ml of blood.