Chemoattractant receptors for interleukin-8 and C5a: expression on peripheral blood leukocytes and differential regulation on HL-60 and AML-193 cells by vitamin D3 and all-trans rètinoic acid

Abstract

Two homologous high‐affinity receptors for the chemoattractant interleukin‐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 receptors. New monoclonal antibodies (mAb) directed against the deduced N‐terminal sequences of the IL‐8RA (mAb SE2) and IL‐8RB (mAb HC2) were generated to determine the IL‐8R expression on human blood leukocytes and two human myeloid cell lines. The C5aR expression was detected using the mAb W17/1. Approximately 107000 C5aR, 55000 IL‐8RA, and 25000 IL‐8RB molecules per cell could be detected on human granulocytes by flow cytometric analysis. On peripheral blood monocytes, 42000 C5aR molecules/cell and 3000 IL‐8RB molecules/cell were expressed. However, we were unable to quantitate IL‐8RA expression, which was detectable but below 2500 molecules per cell and thus outside the standard range for the quantitation of receptor molecules by flow cytometry. On AML‐193 cells, only the IL‐8RB was constitutively expressed, whereas on HL‐60 cells, we could not detect expression of any of the three receptors. Vitamin D₃ (250 ng/ml, 7 days), which has been shown to induce differentiation of AML‐193 and HL‐60 cells into the monocytic phenotype, led to an up‐regulation 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 μM, 7 days), which induces differentiation into the granulocytic phenotype, 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 expression differs from that of its IL‐8RB homolog and may be a late event in leukocyte maturation.