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Heat-stable antigen/CD24 on mouse T lymphocytes: evidence for a costimulatory function.

Hubbe M., Altevogt P.

Heat-stable antigen (HSA)/mouse CD24 (formerly termed Nectadrin) is a membrane glycoprotein with an unusual structure consisting of a small protein core and extensive glycosylation. It is expressed by hematopoietic cells but not by mature T lymphocytes. HSA on accessory cells is an important costimulatory molecule required for the clonal expansion of T lymphocytes. HSA is also involved in cell-cell adhesion events and the isolated antigen has been shown to possess self-binding properties. In the present study we have re-investigated the role of HSA in T cell proliferation. We find that following stimulation of T lymphocytes with concanavalin A or of CD4+ T lymphocytes with a combination of anti-CD3/CD28 monoclonal antibodies (mAb) the HSA antigen is transiently expressed. The expression correlated with the appearance of CD25 and a CD2 activation epitope at the cell surface. Induction of HSA was also seen in vivo on V beta 8+ T lymphocytes in BALB/c mice that were injected with Staphylococcal enterotoxin B. Biosynthetic labeling and analysis of mRNA by reverse transcriptase-polymerase chain reaction showed that HSA was synthesized by activated T lymphocytes. A combination of anti-CD3 and mAb 79 to HSA was incapable of inducing proliferation of purified CD4+ T lymphocytes. However, the antibody strongly enhanced the response obtained with a combination of anti-CD3/CD28 mAb. The augmenting effect of the HSA-specific mAb was dose dependent. Since HSA is bound to the membrane via a glycosyl-phosphatidylinositol (GPI) anchor and GPI-anchored molecules have been implicated in lymphocyte activation, it is conceivable that HSA is not only a costimulatory molecule on accessory cells but is also a signaling molecule in T lymphocytes. The possibility of a homotypic HSA/HSA interaction between T lymphocytes and accessory cells is discussed.

Eur. J. Immunol. 24:731-737(1994) [PubMed] [Europe PMC]

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