We report that M. tuberculosis organisms, but neither PHA nor allogeneic stimulator cells, preferentially activate gamma/delta+ cells within E rosette-purified peripheral blood T cells. gamma/delta+ T cells from purified protein derivative (PPD)-nonimmune healthy donors were enriched by depletion of CD4+ and CD8+ cells; double-negative (DN) cells contained 65-92% gamma/delta+ T cells. Limiting dilution (LD) analyses revealed that 1 of 2-19 purified DN cells proliferated in response to mycobacteria, while frequencies of DN cells proliferating in response to a recombinant 65-kD heat shock protein (hsp 65) of M. tuberculosis/M. bovis were 10-20-fold lower. Established clones of mycobacteria-reactive gamma/delta+ T cells specifically recognized mycobacteria, but neither PPD nor hsp 65. Restimulation of these clones required the presence of PBMC feeder cells; EBV-transformed lymphoblastoid cell lines could not substitute for PBMC. Mycobacteria-reactive gamma/delta+ clones proliferated equally well in the presence of autologous or allogeneic (HLA-DR-different) PBMC feeder cells and thus were not MHC class II restricted. Taken together, these results demonstrate that mycobacteria-reactive gamma/delta+ T cells are present in high frequency in the peripheral blood of healthy individuals, and suggest that hsp 65 of mycobacteria is not a major antigen for gamma/delta+ T cells of normal PPD-nonimmune blood donors.

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mAb directed against the TCR/CD3 complex activate resting T cells. However, TCR/CD3 signaling induces death by apoptosis in immature (CD4+CD8+) murine thymocytes and certain transformed leukemic T cell lines. Here we show that anti-TCR and anti-CD3 mAb induce growth arrest of cloned TCR-gamma delta + T cells in the presence of IL-2. In the absence of exogenous IL-2, however, the very same anti-TCR/CD3 mAb stimulated gamma delta (+)-clones to proliferation and IL-2 production. In the presence of exogenous IL-2, anti-TCR/CD3 mAb induced the degradation of DNA into oligosomal bands of approximately 200 bp length in cloned gamma delta + T cells. This pattern of DNA fragmentation is characteristic for the programmed cell death termed apoptosis. These results demonstrate that TCR/CD3 signaling can induce cell death in cloned gamma delta + T cells. In addition, this report is the first to show that apoptosis triggered by TCR/CD3 signaling is not restricted to CD4+CD8+ immature thymocytes and transformed leukemic T cell lines but can be also observed with IL-2-dependent normal (i.e., TCR-gamma delta +) T cells.

During fetal ontogeny, T cell progenitors entering the thymus undergo a coordinate pathway of differentiation . Discrete steps of intrathymic maturation can be monitored by the sequential appearance of cell surface glycoproteins, of which CD2 (711, sheep erythrocyte receptor) is thought to be the first T lineage-specific differentiation antigen (1). It is only after expression of CD2 that differentiating thymocytes proceed to acquire CD4 plus CD8 antigens, and finally segregate into two mutually exclusive subsets of CD2+CD3'CD4+CD8" and CD2+CD3+CD4-CD8+ mature thymocytes (1, 2). With the appearance of the CD3 molecular complex, thymocytes first express y/b and later a/o TCR heterodimers (3-5). This prevailing view of T cell ontogeny predicts that CD2 is expressed on all CD3 + T cells (1). Recently, however, CD2 -CD3 + T cells have been identified both in fetal human spleen and thymus (6), and in a subset of CD3 +TCRy/b+ peripheral blood T cells from one individual (7). In addition, CD2-stable variants have been selected from the CD3/TCR* leukemic Jurkat line (8). Together, these recently published data suggest that the expression of a functional CD3/TCR complex is not invariably linked to the simultaneous expression of the CD2 differentiation antigen.In this article we show that a minor fraction of CD2-cells can be regularly identified among CD3'TCRa//3+ peripheral blood T cells isolated from healthy donors . In addition, we have established IL-2-dependent long-term clones with a stable CD2-CD3+TCR a/S+ phenotype that do not express detetable levels of CD2 mRNA . Functional studies indicated that CD2-, CD3/TCR+ T cell clones could be induced to proliferate, produce IL-2, and display cytotoxic effector function by mAbs directed against CD3 or TCR. These data identify a previously unrecognized minor subset of CD2-CD3/TCRa/S + human peripheral blood T cells and demonstrate that expression of CD2 is not a prerequisite for the surface expression of a functional CD3/TCR-a/0-molecular complex on mature human T cells.