THE HUMAN MAST-CELL LINE HMC-1 EXPRESSES C5A RECEPTORS AND RESPONDS TO C5A BUT NOT TO C5A(DESARG)

The expression of the receptor for the anaphylatoxin C5a (C5aR, CD88) on the human mast cell line HMC-1 was studied with four anti-C5aR mono clonal antibodies directed to the N-terminal domain of the receptor. A ll antibodies bound to the human mast cell line HMC-1. The binding cou ld be blocked by recombinant C5a and by peptide EX-1 representing amin o residues 1-31 on the N-terminal domain of the C5aR. In addition, FIT C-labelled C5a bound to HMC-1, and this binding could be blocked by un labelled C5a or C5aR antibodies. C5aR-specific mRNA was detected in HM C-1 cells by RT-PCR which confirmed the expression of the C5aR gene ma de by these cells. Lymphocyte-conditioned medium, interferon-gamma or phorbol esters which have been shown to induce a down-regulation of C5 aR on myeloid cells did not influence the expression of C5aR on HMC-1. C5a let to a transient mobilization of intracellular calcium in HMC-1 which could be inhibited by pre incubation of C5a with a C5a-specific antibody. In contrast to findings with granulocytes, HMC-1 did not re spond to C5a (desArg), confirming previous findings with human skin ma st cells. The findings show that (i) although HMC-1 differ from granul ocytes in their responsiveness to C5a (desArg), they express similar C 5aR and (ii) HMC-1 resemble skin mast cells in the expression and func tion of C5aR and may therefore serve as a model in future studies addr essing the biology of this anaphylatoxin receptor on skin mast cells.