Antigen responsiveness during tuberculosis: Regulatory interactions of T cell subpopulations and adherent cells

Previous studies from this laboratory demonstrated that adherent mononuclear cells selectively decreased in vitro tuberculin responses in some anergic patients with tuberculosis; subsequently this adherent suppressor cell was characterized as a monocyte. The current study of 41 patients with active pulmonary tuberculosis examined whether T cell subpopulations also acquired antigenspecific suppressor function during Mycobacterium tuberculosis infection, contributed to monocyte-medlated suppression of tuberculin responses, or both. Alteration in the numbers of circulating T-helper (Leu 3a) and T-suppressor (Leu 2a) cells was not observed in patients with tuberculosis, nor did Leu 2a cells selectively modulate in vitro tuberculin responses. The numbers of circulating Tγ cells, a subset of T cells identified by surface receptors for the Fc portion of IgG (FcγR), was increased twofold in patients with active pulmonary tuberculosis. Depletion of Tγ cells from in vitro cell culture consistently and selectively increased tuberculin responsiveness of T cells from patients with tuberculosis. In addition, in the absence of Tγ cells, monocyte-mediated suppression of tuberculin responses was demonstrated in each patient observed. These studies demonstrate that during M. tuberculosis infection Tγ cells acquire antigen-specific suppressor cell activity and suggest that Tγ cells also contribution to immunoregulation modulating the expression of tuberculin-specific suppression by monocytes.