Identification of haptoglobin as an alternative ligand for CD11b/CD18.
Identification of haptoglobin as an alternative ligand for CD11b/CD18.
复制标题
鉴定触珠蛋白作为 CD11b/CD18 的替代配体。
作者：
S. M. E. Ghmati;E. V. Hoeyveld;J. Strijp;J. Ceuppens;E. Stevens
触珠蛋白是一种急性时相蛋白，具有假定的抗炎活性。我们报告，纯化的荧光素标记的触珠蛋白1-1结合THP 1和U937前单核细胞系，单核细胞，粒细胞，和一个子集的CD 8 + T细胞和NK细胞。对THP 1细胞进行的放射性碘标记触珠蛋白研究与一类受体的特异性结合一致，其密度为每个细胞1.7 x 10（5）个结合位点，亲和力较低，为6.5 x 10（-6）Kd。Ca 2+和Ca 2+与ADP的结合增加。与THP 1和U937细胞的结合可以通过与nonfluoresceinated haptoglobin和纤维蛋白原预孵育来抑制，但不能通过白蛋白、转铁蛋白或α 1-酸性糖蛋白来抑制。纤维蛋白原与CD 11b/CD 18整联蛋白结合。因此，我们研究了触珠蛋白是否具有相同的受体。抗CD 11b mAb 44确实抑制荧光标记的触珠蛋白与THP 1和U937细胞系的结合，触珠蛋白抑制抗CD 11b mAb anti-Leu 15和mAb 44与两种细胞系的结合。抗CD 18 mAb部分抑制荧光标记的触珠蛋白与THP 1和U937的结合，表明MAC-1的β链也参与触珠蛋白结合。抗CD 4、抗CD 11 a或抗CD 11 c mAb与结合珠蛋白结合THP 1细胞之间无干扰。结合珠蛋白与纯化的CD 11b/CD 18的结合表明其直接与受体结合。触珠蛋白是CD 11b/CD 18整合素的另一种低亲和力配体，表明这种急性期蛋白可能在体内调节MAC-1依赖性细胞功能。
Haptoglobin is an acute phase protein with presumed anti-inflammatory activities. We report that purified fluorescein-labeled haptoglobin 1-1 binds to THP1 and U937 promonocytic cell lines, to monocytes, to granulocytes, and to a subset of CD8+ T cells and to NK cells. Studies with radioiodinated haptoglobin on THP1 cells were consistent with specific binding to one class of receptors with a density of 1.7 x 10(5) binding sites per cell and a low affinity of 6.5 x 10(-6) Kd. Binding was increased by Ca2+ and by Ca2+ and ADP. Binding to THP1 and U937 cells could be inhibited by preincubation with nonfluoresceinated haptoglobin and by fibrinogen, but not by albumin, transferrin, or alpha1-acid glycoprotein. Fibrinogen binds to the CD11b/CD18 integrin. We therefore examined whether haptoglobin has the same receptor. The anti-CD11b mAb44 indeed inhibited the binding of fluoresceinated haptoglobin to THP1 and U937 cell lines, and haptoglobin inhibited the binding of the anti-CD11b mAb anti-Leu15 and mAb44 to both cell lines. An anti-CD18 mAb partly inhibited the binding of fluoresceinated haptoglobin to THP1 and U937, indicating that the beta-chain of MAC-1 is also involved in haptoglobin binding. There was no interference between the binding of anti-CD4, anti-CD11a, or anti-CD11c mAb and haptoglobin binding to THP1 cells. Binding of haptoglobin to purified CD11b/CD18 indicates that it binds directly to the receptor. Haptoglobin is an alternative low affinity ligand for the CD11b/CD18 integrin, suggesting that this acute phase protein might regulate MAC-1-dependent cell function in vivo.