Functional thrombin receptors on human T lymphoblastoid cells.
Human alpha-thrombin stimulated five different T lymphoblastoid cell lines to increase intracellular free Ca2+ concentrations, whereas five B cell lines did not similarly respond. The T cell intracellular free Ca2+ increased rapidly, plateaued within 10 to 20 s, and then declined without any measurable sustained intracellular free Ca2+ elevation. Liberation of inositol trisphosphate peaked within 60 s, and a rapid and sustained activation of protein kinase C was induced. The thrombin-specific inhibitor, hirudin, completely blocked the response to alpha-thrombin. Catalytically inactivated forms of alpha-thrombin failed to stimulate the T cells, whereas trypsin, gamma-thrombin (which lacks fibrinogen clotting activity), or the synthetic 14-amino acid thrombin receptor-activation peptide stimulated T cells, but required approximately 10-, approximately 15-, or approximately 100-fold higher concentrations, respectively, when compared to alpha-thrombin. Stimulation by thrombin receptor-activation peptide was desensitized by alpha-thrombin, and vice versa, but alpha-thrombin did not desensitize stimulation by mAb to the TCR/CD3 Ag. The presence of the receptor on T but not on B cells was confirmed by flow-cytometric analysis using a mAb against the human thrombin receptor. These findings demonstrate functional thrombin receptors on T lymphoblastoid cells that may be capable of activating the cells, independently of an ongoing immune response.
Tordai
A
A
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver CO 80206.
Fenton
J W
JW
Andersen
T
T
Gelfand
E W
EW
D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005455:Fluorescent Antibody Technique; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D011493:Protein Kinase C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000032:analysis / Q000276:immunology / Q000502:physiology*; D018179:Receptors, Thrombin; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D013917:Thrombin / Q000276:immunology / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D007295:Inositol Phosphates; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; D011493:Protein Kinase C; D013917:Thrombin; D002118:Calcium