Lee S, Russo D, Redman C M
Lindsley F. Kimball Research Institute, The New York Blood Center, New York 10021, USA.
Semin Hematol. 2000 Apr;37(2):113-21. doi: 10.1016/s0037-1963(00)90036-2.
Two membrane proteins express the antigens that comprise the Kell blood group system. A single antigen, Kx, is carried on XK, a 440-amino acid protein that spans the membrane 10 times, and more than 20 antigens reside on Kell, a 93-kd, type II glycoprotein. XK and Kell are linked, close to the membrane surface, by a single disulfide bond between Kell cysteine 72 and XK cysteine 347. Although primarily expressed in erythroid tissues, Kell and XK are also present in many other tissues. The polymorphic forms of Kell are due to single base mutations that encode different amino acids. Some Kell antigens are highly immunogenic and may cause strong reactions if mismatched blood is transfused and severe fetal anemia in sensitized mothers. Antibodies to KEL1 may suppress erythropoiesis at the progenitor level, leading to fetal anemia. The cellular functions of Kell/XK are complex. Absence of XK, the McLeod phenotype, is associated with acanthocytic red blood cells (RBCs), and with late-onset forms of muscular dystrophy and nerve abnormalities. Kell, by homology, is a member of the neprilysin (M13) family of membrane zinc endopeptidases and it preferentially activates endothelin-3 by specific cleavage of the Trp21-Ile22 bond of big endothelin-3.
两种膜蛋白表达构成凯尔血型系统的抗原。单个抗原Kx由XK携带，XK是一种440个氨基酸的蛋白质，跨膜10次，20多种抗原存在于凯尔蛋白上，凯尔蛋白是一种93kd的II型糖蛋白。XK和凯尔蛋白通过凯尔蛋白半胱氨酸72和XK半胱氨酸347之间的单个二硫键在膜表面附近相连。虽然主要在红细胞组织中表达，但凯尔蛋白和XK也存在于许多其他组织中。凯尔蛋白的多态形式是由于编码不同氨基酸的单碱基突变。一些凯尔抗原具有高度免疫原性，如果输入不匹配的血液，可能会引起强烈反应，并导致致敏母亲体内的胎儿严重贫血。针对KEL1的抗体可能在祖细胞水平抑制红细胞生成，导致胎儿贫血。凯尔蛋白/XK的细胞功能很复杂。缺乏XK即麦克劳德表型，与棘状红细胞、迟发性肌营养不良和神经异常有关。通过同源性分析，凯尔蛋白是膜锌内肽酶中性肽链内切酶（M13）家族的成员，它通过特异性切割大内皮素-3的Trp21-Ile22键优先激活内皮素-3。
