TG cell involvement in the leukocyte adherence inhibition phenomenon

Peripheral blood mononuclear cells (PBMC), T-cells, non-T-cells, TG cells, and TM cells were tested for leukocyte adherence inhibition (LAI) reactivity to purified protein derivative (PPD) in normal human volunteers to determine the reactive cell subfractions. T-cells were separated by sheep red blood cell rosetting and TM and TG cells by rosetting with anti-ox red blood cell (ORBC) IgM- and IgG-treated ORBC. Fresh PBMC, T-cells, and TG cells gave positive LAI reactivity to PPD in PPD-positive donors only. PBMC that had undergone 24-hour incubation or extensive washing, non-T-cells, and TM cells were unreactive. All cell subfractions were negative in PPD-negative donors. Indirect LAI assay was performed on the spent media from overnight incubation of unstimulated PBMC and also following a 1-hour incubation of the various cell subfractions obtained from a PPD-reactive donor with PPD. Positive reactions, indicating the release of an LAI factor (LAIF), were obtained with the spent media and with the T-cell and TG cell subfractions following PPD stimulation, whereas non-T-cell and TM cell subfractions yielded no reactivity. Incubation of sensitized T-cells with PPD in the presence of cycloheximide and preincubation of T-cells for 24 hours with cycloheximide before PPD exposure failed to inhibit LAI reactivity. These data suggest that T-cells, specifically TG cells, can release LAIF upon specific antigen stimulation with PPD, whereas non-T-cell and TM cell subpopulations fail to respond to the same stimulus. LAIF may also be released into the culture media with prolonged (overnight) incubation in artificial media or with extensive washing. Inhibition of protein synthesis during antigen exposure or up to 24 hours before antigen exposure does not appear to inhibit LAI reactivity.