Importance of HLA‐D antigens for the cooperation between human monocytes and T lymphocytes

Abstract

Abstract The ability of autologous and allogeneic monocytes to restore the responsiveness of purified T lymphocytes to tuberculin (PPD) was studied in twelve different experiments involving eleven unrelated T lymphocyte donors and a large number of related and unrelated monocyte donors. T lymphocyte suspensions were prepared by passage of peripheral blood mononuclear cell suspensions through Ig‐anti‐Ig‐coated columns. Monocyte‐enriched suspensions were prepared from mononuclear suspensions by density gradient centrifugation on albumin solution and added to the T cell suspension in a final concentration of 3%. Autologous monocytes and monocytes from related donors sharing one HLA haplotype with the T cell donor partly restored the responsiveness to PPD, and so did monocytes from unrelated donors who shared HLA‐D alleles with the T cells. None of eight monocyte suspensions from eight unrelated donors sharing no HLA‐D antigens with the T cell donor were able to restore the responsiveness to PPD. The difference between HLA‐D‐sharing and nonsharing monocytes could not be explained by a simultaneous allogeneic reaction, as the addition of monocytes autologous with the T cells to mixtures of non‐HLA‐D‐sharing T cells and monocytes partly restored the response. Moreover, experiments with the addition of PPD to ordinary mixed leukocyte cultures revealed only a moderate depression on the PPD response. It is concluded that in man – as in mice and guinea pigs – some HLA‐D identity between monocytes and T lymphocytes is necessary for a cooperation to take place in the secondary immune response. This observation emphasizes the homology between HLA‐D antigens in man and Ia antigens in animals.