CD88 ANTIBODIES SPECIFICALLY BIND TO C5AR ON DERMAL CD117(+) AND CD14(+) CELLS AND REACT WITH A DESMOSOMAL ANTIGEN IN HUMAN SKIN

The expression of the C5aR (CD88) on human epidermal and dermal cells was studied with five anti-C5aR mAb directed to the N-terminal domain of the receptor. All mAb bound to suspended dermal CD117(+) mast cells and to dermal CD14(+) cells. The binding to CD14(+) and CD117(+) cell s could be blocked by rC5a and by peptide EX-1 representing amino acid residues 1-31 of the C5aR. In acetone-fixed frozen or in paraformalde hyde-fixed, paraffin-embedded tissue, we detected a binding of the Abs to dermal perivascular cells and, additionally, to keratinocytes and dermal epithelial cells that could be blocked by EX-1. Immunoelectromi croscopy revealed a binding of anti-C5aR mAb to desmosomal regions in human epidermis. However, the following results indicate that CD88 mAb cross-react with epithelium in a specific way: 1) the binding to susp ended epidermal cells and to the epidermal cell line HaCat could be bl ocked by EX-1 but not by rC5a; 2) FITC-labeled C5a bound to CD117(+) a nd to CD14(+) cells but not to epidermal cells; 3) C5a led to transien t calcium fluxes in CD14(+) and CD117(+) dermal but not in epidermal c ells; 4) C5aR mRNA was detectable by reverse transcription PCR in gran ulocytes but not in keratinocytes or in HaCat. Our results show that C D88 mAb are good tools for the investigation of the C5aR on hemopoieti c cells. Results with epithelial cells should be considered with cauti on, as the binding of CD88 mAb that were raised to a synthetic peptide sequence may be due to a cross-reactivity.