A high proportion of T lymphocytes that infiltrate H-2-incompatible heart allografts in vivo express genes encoding cytotoxic cell-specific serine proteases, but do not express the MEL-14-defined lymph node homing receptor.

The role of cytotoxic cells in in vivo immune functions such as allograft rejection is unknown. To begin to assess the function of cytolytic cells in vivo we have begun with cytolytic cell-specific functional molecules: we have isolated and characterized cytolytic cell-specific cDNA clones from cytolytic T cell clones, both encoding distinct serine esterases. The HF gene encodes a trypsin-like enzyme while the C11 gene encodes an enzyme with likely specificity for acidic residues. Here we demonstrate, using in situ hybridization with RNA probe, that both genes are expressed selectively in a subset of T lymphocytes that have infiltrated cardiac allografts. The phenotype of these cells is consistent with the most frequent phenotype of active CTL raised in vitro: they are predominantly CD4-, CD8+, MEL-14- T cell blasts. Thus the expression of these genes, each of which encodes serine esterase found in killer cell granules in vitro, is a valid marker for these cells in vivo as well. The kinetics of their accumulation is consistent with, but not proof of, a putative role in allograft rejection. It is likely that HF and C11 gene expression will be of diagnostic value.

Alloreactive cloned T cell lines. I. Interactions between cloned amplifier and cytolytic T cell lines.

Several T cell clones have been derived by limiting dilution of secondary mixed leukocyte culture cells stimulated by H-2- and M locus (Mls)-disparate spleen cells. When examined for the expression of cytolytic activity and the ability to proliferate, these cell clones can be classified into two major categories. One type of cell is noncytolytic; when cultured with irradiated spleen cells, such clones proliferate in response to Mls determinants. Some, but not all, of these clones express Lyt-1 alloantigens. The other type of cell is cytolytic; these clones do not proliferate when cultured with irradiated allogeneic spleen cells unless supernatant fluid (SF) is added. These cytolytic clones express Lyt-2 alloantigens. Some cytolytic clones are specific for H-2Kd and others for H-2Dd alloantigens. Still other cytolytic cell clones exhibit cross-reactive lysis of different H-2-bearing tumor and Con A blast target cells. Noncytolytic T cell clones, when stimulated by Mls antigens, were examined for their ability to promote proliferation of cytolytic T cell clones. All of the noncytolytic cell clones tested were able to promote proliferation of cytolytic cell clones with the concomitant expression of cytolytic activity directed toward the original stimulating alloantigen (H-2d). Amplification of cytolytic activity was dependent upon stimulation of the noncytolytic amplifier T cell clones by Mls antigens. Specific alloantigen (signal 1), however, was not required for proliferation of the cytolytic cell clones; the amplifying signal (signal 2), delivered by the amplifier cell clones, was sufficient alone to promote proliferation of the cytolytic cell clones. Whereas proliferation of the amplifier cells was radiosensitive, the generation of the soluble amplifying signal was radioresistant. Amplification of cytolytic activity was observed when either amplifier cells were physically separated from responding cytolytic cells in Marbrook cultures or when cytolytic cells were cultured with SF collected from amplifier cell cultures. The amplifying factors were neither antigen specific nor strain specific and could be produced by Lyt-1- cells. The availability of cloned T cell lines that retain specific biologic function offers unique opportunities to characterize cell surface proteins and cell-cell interactions.