Zhang H, Zhong Z, Pirofski L A
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Infect Immun. 1997 Apr;65(4):1158-64. doi: 10.1128/iai.65.4.1158-1164.1997.
Cryptococcus neoformans causes meningitis in 6 to 8% of individuals with AIDS. Recently, immunotherapeutic modalities including antibody therapy have been proposed for the treatment of cryptococcal meningitis in AIDS patients. This is a rational approach because existing antifungal agents fail to eradicate the infection in the setting of profound immunosuppression. Both murine and human antibodies elicited by the investigational cryptococcal capsular polysaccharide vaccine glucuronoxylomannan-tetanus toxoid (GXM-TT) have been shown to be biologically functional in different model systems. The human immunoglobulin M (lambda) GXM monoclonal antibody (MAb) 2E9 expresses idiotypes that are also found in naturally occurring anti-GXM antibodies and opsonic GXM-TT sera. However, the specificity of human anti-GXM antibodies and their possible role in protection against cryptococcosis are not known. In an effort to discover epitopes that are recognized by human anti-GXM antibodies, we screened a random decapeptide phage display library with the human anti-GXM MAb 2E9. An enzyme-linked immunosorbent assay (ELISA)-based screening method led to the selection of phages with peptide inserts that bound 2E9 and inhibited 2E9-GXM binding. Analysis of the amino acid sequences of these phages revealed an increased frequency of combinations of QTGLD residues. Inhibition ELISAs demonstrated that phages with QTG/TL/D motifs inhibited 2E9-GXM binding better than phages with different motifs. A peptide synthesized from one of the inhibitory phages, peptide 13 (GMDGT QLDRW), inhibited GXM binding to solid-phase 2E9 and 2E9 binding to solid-phase GXM. Peptide 13 also inhibited the GXM binding of GXM-TT immune sera and naturally occurring serum antibodies from human immunodeficiency virus (HIV)-negative, but not HIV-positive, individuals. Taken together, our data indicate that the peptide epitopes selected by 2E9 mimic GXM epitopes and that peptide 13 may be a mimotope of a GXM epitope that is recognized by human anti-GXM antibodies.
新型隐球菌在6%至8%的艾滋病患者中会引发脑膜炎。最近，包括抗体疗法在内的免疫治疗方式已被提议用于治疗艾滋病患者的隐球菌性脑膜炎。这是一种合理的方法，因为现有的抗真菌药物在深度免疫抑制的情况下无法根除感染。研究用的隐球菌荚膜多糖疫苗葡糖醛酸木聚糖甘露聚糖-破伤风类毒素（GXM-TT）引发的鼠源和人源抗体在不同模型系统中均已显示具有生物学功能。人免疫球蛋白M（λ）GXM单克隆抗体（MAb）2E9表达的独特型也存在于天然存在的抗GXM抗体和具有调理作用的GXM-TT血清中。然而，人抗GXM抗体的特异性及其在预防隐球菌病中的可能作用尚不清楚。为了发现人抗GXM抗体识别的表位，我们用抗GXM人单克隆抗体2E9筛选了一个随机十肽噬菌体展示文库。基于酶联免疫吸附测定（ELISA）的筛选方法导致选择了带有与2E9结合并抑制2E9-GXM结合的肽插入片段的噬菌体。对这些噬菌体氨基酸序列的分析显示QTGLD残基组合的频率增加。抑制性ELISA表明，具有QTG/TL/D基序的噬菌体比具有不同基序的噬菌体能更好地抑制2E9-GXM结合。从一种抑制性噬菌体合成的肽，肽13（GMDGT QLDRW），抑制GXM与固相2E9结合以及2E9与固相GXM结合。肽13还抑制GXM-TT免疫血清和来自人类免疫缺陷病毒（HIV）阴性而非HIV阳性个体的天然血清抗体的GXM结合。综上所述，我们的数据表明2E9选择的肽表位模拟GXM表位，并且肽13可能是被人抗GXM抗体识别的GXM表位的模拟表位。
