Human T cells express the C5a receptor and are chemoattracted to C5a

The anaphylatoxin C5a is a potent mediator of inflammation that exerts a br oad range of activity on cells of the myeloid lineage, In this study, we pr esent the first evidence that human T cells express the C5a receptor (C5aR) and are chemotactic to C5a, Using FAGS analysis, we found that the C5aR wa s expressed at a low basal level on unstimulated T cells and was strikingly up-regulated upon PHA stimulation in a time- and dose-dependent manner. CD 3(+) sorted T cells as well as Jurkat T cells were shown to express C5aR mR NA as assessed by RT-PCR, Moreover, semiquantitative RT-PCR analysis demons trated that C5aR mRNA was do downregulated in purified T cells upon long-te rm PHA stimulation. To demonstrate that C5a was biologically active on T ce lls, we investigated the chemotactic activity of C5a and observed that puri fied CD3+ T cells are chemotactic to C5a at nanomolar concentrations. Final ly, using a combination of in situ hybridization and immunohistochemistry, we showed that the T cells infiltrating the central nervous system during e xperimental allergic encephalomyelitis express the C5aR mRNA, In summary, t hese results suggest that C5a exerts direct effects on T cells and could be involved in the trafficking of T cells under physiological and pathologica l conditions, including inflammatory diseases of the central nervous system .