Distribution and regulation of expression of the putative human chemokine receptor HCR in leukocyte populations

Human chemokine receptor (HCR) is a putative chemokine receptor sharing high similarity with CCR1, CCR2, CCR3 and CCR5. Its gene is located within the main cluster of CC-chemokine receptor genes, in the 3p21 region of the human genome. We generated monoclonal antibodies directed at human HCR, and studied its distribution in human leukocyte populations and cell lines, and its regulation following maturation or activation of these populations. In peripheral blood leukocytes, HCR is expressed on CD4(+) and CD8(+) T lymphocytes, including most memory and part of naive cells, but is absent from B cells. Expression of HCR was enhanced following stimulation of T cells by OKT3 and IL-2. HCR is present on monocytes and macrophages. Monocyte-derived dendritic cells harbored HCR, and expression was enhanced following stimulation by lipopolysaccharides, poly (I:C), IFN-gamma or CD40L. Neutrophils strongly expressed HCR. A similar distribution was found in bone marrow, and HCR was also expressed in CD34(+) precursors. Expression of HCR and its regulation were confirmed by real-time PCR. In a panel of human tissues, we found abundant HCR transcripts in thymus, spleen, lymph nodes and lung. This large distribution across leukocyte populations, and the up-regulation during DC maturation, represent a new profile among chemokine receptors. We speculate that HCR responds to inflammatory chemokines, and might be involved in the interaction between antigen presenting and T cells, and in hematopoiesis.