Increased expression of complement receptor type 1 (CR1, CD35) on human peripheral blood T lymphocytes after polyclonal activation in vitro.

The receptor for C3b and C4b--complement receptor type 1 (CR1, CD35)--is present on a variety of cell types including erythrocytes, phagocytic cells, B lymphocytes and a small subpopulation of T lymphocytes. The function of the receptor varies according to the different cell types, but on T lymphocytes the function is as yet not known. The present study concerns the influence of polyclonal stimulation on CR1-expressing T lymphocytes. Incubation with PHA resulted in a dose-dependent increase in the number of CR1-positive T lymphocytes. The CR1-expression T lymphocytes were found in both the CD4- and the CD8-positive subpopulation, but a significant stimulatory increase was only found in the CD4-positive population. A significant increase in the number of CR1-expressing T lymphocytes was found when monocytes were present during stimulation, indicating an importance of monocytes and/or monocyte products. However, the increase was not regulated by arachidonic acid metabolites of the cyclo-oxygenase pathway as indomethacin failed to inhibit the increase. Neither did rIL-1 alpha, rIL-1 beta, rTNF alpha nor rIL-6 alter the number of CR1-expressing T lymphocytes. The results of this study indicate a role for CR1 on T lymphocytes in the regulation of the immune system.