Danielsson C, Pascual M, French L, Steiger G, Schifferli J A
Laboratory of Immunonephrology, Medizinische Klinik B, Department Innere Medizin, Kantonsspital Basel, Switzerland.
Eur J Immunol. 1994 Nov;24(11):2725-31. doi: 10.1002/eji.1830241123.
The soluble form of complement receptor type 1 in human plasma (sCR1) might correspond to the shedding of the receptor by proteolytic cleavage at the cell surface. A new enzyme-linked immunosorbent assay (ELISA) was established to specifically measure membrane-bound CR1 using a rabbit polyclonal antibody against a 19-amino acid peptide corresponding to the C-terminal sequence of the intracellular domain of CR1 (mCR1-ELISA). This ELISA measured CR1 from solubilized erythrocyte membranes, polymorphonuclear leukocytes (PMN), a B lymphocyte cell line and renal podocyte-derived urinary vesicles in a dose-dependent manner. In contrast, and similarly to recombinant soluble CR1 which lacks the intracellular domain of CR1, plasmatic sCR1 was not recognized, suggesting that sCR1 corresponds to an extracellular fragment of whole CR1. In vitro, PMN were shown to release a soluble form of CR1 which was also not recognized in the mCR1-ELISA, and whose size was smaller (5 kDa) than the CR1 of PMN cell membranes. The release of soluble CR1 was highest for PMN and HL60 cells, followed by U937 cells and three different B lymphocyte cell lines, whereas T lymphocyte cell lines did not release soluble CR1. The levels of CR1 gene expression were also higher in PMN compared to remaining blood leukocytes and the different cell lines tested above. Incubation of PMN with formyl-methionyl-leucyl-phenylalanine, tumor necrosis factor-alpha or lipopolysaccharide accelerated the release of soluble CR1, and incubation with granulocyte/macrophage colony-stimulating factor resulted in sustained CR1 gene expression and higher total soluble CR1 release. Our results suggest that soluble CR1 is produced by cleavage of cell surface CR1, and that a large fraction of human plasma sCR1 is cleaved from PMN. The release of sCR1 by leukocytes may play a role in the control of complement activation at sites of inflammation.
人血浆中可溶性补体受体1型（sCR1）可能对应于细胞表面通过蛋白水解切割产生的受体脱落。建立了一种新的酶联免疫吸附测定法（ELISA），使用针对与CR1细胞内结构域C端序列对应的19个氨基酸肽的兔多克隆抗体，特异性测量膜结合的CR1（mCR1-ELISA）。该ELISA以剂量依赖方式测量来自溶解的红细胞膜、多形核白细胞（PMN）、B淋巴细胞系和肾足细胞衍生的尿囊泡中的CR1。相反，与缺乏CR1细胞内结构域的重组可溶性CR1类似，血浆sCR1未被识别，这表明sCR1对应于完整CR1的细胞外片段。在体外，PMN被证明可释放一种可溶性CR1形式，其在mCR1-ELISA中也未被识别，且其大小比PMN细胞膜的CR1小（5 kDa）。可溶性CR1的释放对于PMN和HL60细胞最高，其次是U937细胞和三种不同的B淋巴细胞系，而T淋巴细胞系不释放可溶性CR1。与其余血液白细胞和上述不同细胞系相比，PMN中CR1基因表达水平也更高。用甲酰甲硫氨酰亮氨酰苯丙氨酸、肿瘤坏死因子-α或脂多糖孵育PMN会加速可溶性CR1的释放，而用粒细胞/巨噬细胞集落刺激因子孵育会导致CR1基因持续表达和更高的总可溶性CR1释放。我们的结果表明，可溶性CR1是由细胞表面CR1的切割产生的，并且人血浆sCR1的很大一部分是从PMN切割而来的。白细胞释放sCR1可能在炎症部位补体激活的控制中起作用。
