CHEMOATTRACTANT RECEPTORS FOR INTERLEUKIN-8 AND C5A - EXPRESSION ON PERIPHERAL-BLOOD LEUKOCYTES AND DIFFERENTIAL REGULATION ON HL-60 AND AML-193 CELLS BY VITAMIN-D-3 AND ALL-TRANS-RETINOIC ACID

Two homologous high-affinity receptors for the chemoattractant interle ukin-8, IL-8RA and IL-8RB, and one for the chemoattractant C5a (C5aR) have been cloned. These membrane proteins are members of the rhodopsin superfamily of G-protein coupled seven-transmembrane segment receptor s. New monoclonal antibodies (mAb) directed against the deduced N-term inal sequences of the IL-8RA (mAb SE2) and IL-8RB (mAb HC2) were gener ated to determine the IL-8R expression on human blood leukocytes and t wo human myeloid cell lines. The C5aR expression was detected using th e mAb W17/1. Approximately 107 000 C5aR, 55 000 IL-8RA, and 25 000 IL- 8RB molecules per cell could be detected on human granulocytes by flow cytometric analysis. On peripheral blood monocytes, 42 000 C5aR molec ules/cell and 3000 IL-8RB molecules/cell were expressed. However, we w ere unable to quantitate IL-8RA expression, which was detectable but b elow 2500 molecules per cell and thus outside the standard range for t he quantitation of receptor molecules by flow cytometry. On AML-193 ce lls, only the IL-8RB was constitutively expressed, whereas on HL-60 ce lls, we could not detect expression of any of the three receptors. Vit amin D-3 (250 ng/ml, 7 days), which has been shown to induce different iation of AML-193 and HL-60 cells into the monocytic phenotype, led to an upregulation of IL-8RB and C5aR in both cell lines in the absence of any expression of IL-8RA. In contrast, all-trans retinoic acid (0.1 mu M, 7 days), which induces differentiation into the granulocytic ph enotype, led to an up-regulation of IL-8RB in AML-193 cells and to an expression of IL-8RB and C5aR in HL-60 cells. Again, neither cell line expressed IL-8RA. These findings suggest that regulation of IL-8RA ex pression differs from that of its IL-8RB homolog and may be a late eve nt in leukocyte maturation.