Absorption of normal lymphocytes on allogeneic spleen monolayers: depletion of alloreactivity is due to inhibition of CTL induction by released monolayer cells.

Abstract

A technique for the haplotype-specific depletion of precursors of alloreactive cytolytic T lymphocytes (CTL-P) by absorption of unprimed spleen cells on allogeneic lymphocyte monolayers has been examined. When H-2d spleen cells were incubated on monolayers of H-2b spleen cells and the nonadherent cells were cultured in mixed leukocyte culture (MLC), CTL activity generated against the monolayer haplotype was 30- to 1000-fold lower than the equivalent cultures of unabsorbed H-2d cells. Cytolytic reactvity to a 3rd-party haplotype, H-2k, was reduced no more than 6-fold. However, culture of the same cells at limiting dilution indicated that the frequency of CTL-P against the monolayer haplotype in monolayer-nonadherent H-2d populations was not significantly different from the frequency in normal H-2d spleen. It was noted that MLC of monolayer-nonadherent H-2d populations were highly cytolytic for H-2d target cells. This reaction was reduced and the ability to generate anti-H-2b CTL was restored when the nonadherent cells were treated with anti-H-2b antibody and complement to eliminate contaminating monolayer cells released during absorption, and when monolayers were prepared from spleen cells depleted of Lyt 2-bearing cells (and hence CTL-P). These data suggested that the reduction in anti-H-2b reactivity of monolayer-nonadherent cells in MLC was due to inhibition by the competing anti-H-2d reaction of contaminating, monolayer-derived CTL-P. Although fluorescent labeling of monolayer cells indicated that these cells represented only 10% of the nonadherent population, flow cytometry and further limiting dilution analysis demonstrated that cells that detached from H-2b monolayers during absorption were enriched 2-fold in T lymphocytes and CTL-P over normal spleen. The strength of the anti-H-2d reaction by a minority of monolayer cells can thus be attributed both to the higher frequency of H-2b anti-H-2d than H-2d anti-H-2b CTL-P in spleen populations and to the preferential detachment of monolayer T lymphocytes during absorption.