Thy-1 functions as a signal transduction molecule in T lymphocytes and transfected B lymphocytes.

Thy-1, a glycoprotein of relative molecular mass 25,000 (25K), is a major constituent of the cell surface of mouse thymocytes, peripheral T cells and neurones. In man, Thy-1 is present on neurones and on a small percentage of thymocytes, but is absent from peripheral T cells. The amino-acid and complementary DNA sequences of Thy-1 indicate that it has a structure similar to an isolated V (variable region) domain of immunoglobulin. Although the function of Thy-1 is unknown, the ability of different anti-Thy-1 monoclonal antibodies to activate murine T cells or induce functional changes in neuronal cells in vitro suggests that Thy-1 is involved in transmembrane signalling. We now show that crosslinking of murine Thy-1 triggers a rapid rise in the cytoplasmic free calcium concentration ([Ca2+]i), not only in murine T cells and Thy-1.2-transfected human T cells, but also in murine B-lymphoma cells transfected with the murine thy-1.2 gene. These results indicate that the generation and transduction of the signal leading to the rise in [Ca2+]i is independent of the T-cell receptor and other T-cell-specific molecules. The preservation of the [Ca2+]i-modulating function of Thy-1 in various lymphoid cells of two species further suggests that the necessary signal either originates in the Thy-1 molecule itself or is generated in concert with a highly conserved molecules(s) associated with Thy-1.

The involvement of suppressor T cells in Ir gene regulation of secondary antibody responses of primed (responder X nonresponder)F1 mice to macrophage-bound L-glutamic acid60-L-alanine30-L-tyrosine.

(Responder [R] X nonresponder [NR])F1 mice give indistinguishable primary in vitro plaque-forming cell (PFC) responses to either R or NR parental macrophages (Mphi) pulsed with the Ir-gene controlled antigen L-glutamic acid60-L-alanine30-L-tyrosine10 (GAT). However, such (R X NR)F1 mice, if primed to GAT, retained in vitro responsiveness to GAT-R-Mphi, but no longer responded to GAT-NR-Mphi. This suggested (a) a possible Mphi-related locus for Ir gene activity in this model, and (b) the occurrence of active suppression after priming with GAT leading to a selective loss of the usual primary responsiveness of (R X NR)F1 mice to GAT-NR-Mphi. This latter interpretation was tested in the current study. [Responder C57BL/6 (H-2b) X nonresponder DBA/1 (H-2q)]F1 mice were primed with 100 microgram GAT in pertussis adjuvant. 4-8 wk later, spleen cells from such mice were tested alone or mixed with normal unprimed F1 spleen cells for PFC responses to GAT-R-Mphi and GAT-NR-Mphi. The primed cells failed to respond to GAT-NR-Mphi, and moreover, actively suppressed the normal response of unprimed F1 cells to GAT-NR-Mphi. If the primed spleen cell donor had been treated with 5 mg/kg cyclophosphamide 3 days before priming or with 5-10 microliter/day of an antiserum to the I-Jb subregion [B10.A(5R) anti B10.A(3R)] during the first 4 days postpriming (both procedures known to inhibit suppressor T-cell activity), cells from such mice responded in secondary culture to both GAT-R-Mphi and also GAT-NR-MPhi. In addition, such spleen cells no longer were capable of suppressing normal F1 cells in response to GAT-NR-Mphi. Similar data were obtained using [CBA (H-2k) X DBA/1 (H-2q)]F1. Further, it was shown that (a) primary responsiveness to GAT-NR-Mphi was not an artifact of in vitro Mphi pulsing, because in vivo GAT-pulsed Mphi showed the same activity and (b) the secondary restriction for Mphi-antigen presentation was controlled by H-2 linked genes. These data suggest an important role for suppressor T cells in H-2 restricted secondary PFC responses, and also provide additional support for the hypothesis that Ir-gene controlled differences in Mphi antigen presentation are related to both suppressor cell generation and overall responsiveness in the GAT model.