Differential binding of chemokines to macrophages and neutrophils in the human inflamed synovium

In chronic inflammatory foci, such as the rheumatoid joint, there is enhanced recruitment of phagocytes from the blood into the tissues. Chemokines are strongly implicated in directing the migration of these cells, although little is known regarding the chemokine receptors that could mediate their chemotaxis into the joint tissue. Therefore the objective of the study was to identify chemokine binding sites on macrophages and neutrophils within the rheumatoid synovium using radiolabeled ligand binding and in situ autoradiography. Specific binding sites for CCL3 (macrophage inflammatory protein-1α), CCL5 (RANTES), CCL2 (monocyte chemoattractant protein-1) and CXCL8 (IL-8) were demonstrated on CD68(+) macrophages in the subintimal and intimal layers. The number and percentage of intimal cells that bound chemokines were greater in inflamed regions compared to noninflamed regions. The intensity of intimal binding varied between chemokines with the rank order, CCL3 > CCL5 > CCL2 > CXCL8. Neutrophils throughout the synovium bound CXCL8 but did not show any signal for binding CCL2, CCL3 or CCL5. Immunohistochemistry showed that both CXCR1 and CXCR2 are expressed by macrophages and neutrophils in the rheumatoid and nonrheumatoid synovia, suggesting that both of these receptors are responsible for the CXCL8 binding. The chemokine binding sites described on phagocytes may be involved in the migration of these cells into the inflamed joint.

在类风湿关节这类慢性炎症病灶中，血液中的吞噬细胞向组织内的募集水平显著升高。尽管目前对介导吞噬细胞趋化进入关节组织的趋化因子受体（chemokine receptors）尚缺乏深入了解，但趋化因子（chemokines）在引导这类细胞迁移的过程中发挥关键作用。因此本研究的目标为：利用放射性配体结合法（radiolabeled ligand binding）与原位放射自显影术（in situ autoradiography），鉴定类风湿滑膜组织内巨噬细胞与中性粒细胞表面的趋化因子结合位点。
研究在内膜下层与内膜层的CD68阳性（CD68(+)）巨噬细胞上，检测到了CCL3（巨噬细胞炎症蛋白-1α，macrophage inflammatory protein-1α）、CCL5（RANTES）、CCL2（单核细胞趋化蛋白-1，monocyte chemoattractant protein-1）以及CXCL8（IL-8）的特异性结合位点。与非炎症区域相比，炎症区域内结合趋化因子的内膜细胞数量及占比均更高。内膜层的趋化因子结合强度因配体种类而异，排序为CCL3 > CCL5 > CCL2 > CXCL8。
滑膜组织内的中性粒细胞可结合CXCL8，但未检测到其结合CCL2、CCL3或CCL5的信号。免疫组织化学（immunohistochemistry）结果显示，类风湿滑膜与非类风湿滑膜中的巨噬细胞及中性粒细胞均表达CXCR1与CXCR2，提示这两种受体均介导了CXCL8的结合。
本研究在吞噬细胞表面鉴定得到的趋化因子结合位点，可能参与了这类细胞向炎症关节的迁移过程。