狼瘡病人血清中抗中性白血球抗體的免疫活性,對應抗原的鑑定,及臨床應用(2/3)

Abstract

由於血清中有抗中性白血球抗體(anti-PMN antibodies)的存在，引起中 性球數目的減少以及功能上的缺陷，致使全身性紅斑狼瘡病人(SLE)易受 細菌的感染。然而SLE 病人血清中的anti-PMN 的對應抗原以及病理機轉 為何？在文獻上很少報告。在本研究中，我們以PMN cellular ELISA 法發 現約有20%的SLE 病人血清中含有anti-PMN 抗體。我們也發現在PMN 細胞表面的50kDa 分子為anti-PMN 抗體的對應抗原之一。以免疫抗體篩 選法，基因選殖及核甘酸序列分析證實50kDa 蛋白是為SSB/La 分子。我 們將活動性SLE病人的血清流經SSB/La-結合的親和性層析管柱純化出抗 SSB/La 抗體。本抗體會結合於PMN 細胞表面而後貫穿進入細胞內，引起 很多的生物活性，包括抑制吞食作用、加速細胞凋亡、以及增加IL-8 的 產生。這些生體外的結果顯示anti-SSB/La 抗體乃屬anti-PMN autoantibodies 的一種，會進入白血球內引起SLE 病人的白血球減少及機 能異常。

Decreased number and impaired functions of polymorphonuclear neutrophils (PMN) due to the presence of anti-PMN autoantibodies in the serum render patients with systemic lupus erythematosus susceptible to bacterial infections. However, the cognate antigens and pathological mechanisms of anti-PMN autoantibodies in SLE are rarely reported in the literature. In this study, we found approximately 20% of SLE sera contained anti-PMN autoantibodies detected by human PMN-coated cellular ELISA. A membrane protein with molecular weight of 50 kDa was identified as the cognate antigen of anti-PMN in Western blot after membrane-biotinylation and strptavidin column elution. The 50kDa molecule was proved to be SSB/La after immunoscreening, molecular cloning and nucleotide sequencing of the gene from the human leukocyte cDNA library. Human anti-SSB/La autoantibodies purified from active SLE sera passing through the recombinant SSB/La conjugated Sepharose 4B affinity column could bound and penetrate into normal human PMN. Functional analysis revealed that the anti-SSB/La autoantibodies exerted a number of potent effects on human PMN, including suppressed phagocytosis, accelerated apoptosis and enhanced IL-8 production. These in vitro results suggest that anti-SSB/La is one of the anti-PMN autoantibodies capable of penetrating into PMN and responsible for neutropenia and functional impairment of PMN in patients with SLE.