IDENTIFICATION AND CHARACTERIZATION OF THE COMPLEMENT C5A ANAPHYLATOXIN RECEPTOR ON HUMAN ASTROCYTES

The C fragment C5a exerts its important physiologic and pathologic eff ects through interaction with a specific C5a receptor (C5aR) which is highly expressed on polymorphonuclear leukocytes and some other leukoc ytes, The presence of this receptor on epithelia and endothelia has re cently been documented, raising the possibility that these other cells might also respond to locally generated C5a, C has been implicated in several brain disorders, notably demyelination and neurodegeneration, and cells within brain can synthesize a complete C system. It is thus of interest to examine the mechanisms by which C damages or activates brain cells. To this end we have examined the expression on human fet al astrocytes and astrocyte-derived cell lines of receptors for C frag ments. We here report that human astrocytes and cell lines express a r eceptor for C5a (48 to 72 x 10(3) copies/cell), which is indistinguish able at the protein or mRNA level from that in leukocytes. The astrocy te C5aR was recognized by five different specific Abs, which revealed by Western blotting a protein of 40 to 45 kDa in primary human astrocy tes and astrocyte tell lines. Expression was confirmed by RT-PCR using multiple primers. Neither inflammatory cytokines nor PMA caused up-re gulation of the receptor on astrocytes, The receptor was functional in that addition of C5a (1 nM to 100 nM) or, at high doses (100 nM), C5a (desArg), triggered a calcium transient in astrocytes. We propose that C5aR expression on astrocytes plays an important role in control of i nflammation in brain and may be a central component of C-mediated brai n injury.