Peterson E M, Cheng X, Pal S, de la Maza L M
Department of Pathology, University of California, Irvine 92717.
Infect Immun. 1993 Feb;61(2):498-503. doi: 10.1128/iai.61.2.498-503.1993.
Monoclonal antibodies (MAbs) E-4, E-21, and DIII A3, which recognize the same or similar overlapping peptides in the variable domain IV of the major outer membrane protein of Chlamydia trachomatis but differ in isotype, were used in a complement-independent (CI) in vitro neutralization assay. These MAbs had previously been shown to neutralize chlamydial infectivity in HeLa 229 cells in a complement-dependent assay. In this report, all three MAbs neutralized chlamydial infectivity in HaK cells in a CI assay. However, when HeLa cells were used as the host cell, MAb E-4 (immunoglobulin G2b [IgG2b]) and MAb DIII A3 (IgG2b) failed to neutralize infectivity, while MAb E-21 (IgG1) neutralized chlamydial infectivity. These findings are consistent with the proposal that because of the presence of Fc gamma RIII receptors, HeLa cells facilitate infectivity and thus block neutralization through the uptake of an IgG2b-chlamydia complex. Since Fc gamma RIII receptors do not bind or bind poorly to IgG1, neutralization of C. trachomatis by MAb E-21 in HeLa cells is also corroborative evidence for the role of Fc gamma RIII receptors in this interaction. A fivefold enhancement of infectivity was seen when 10 and 1 micrograms of MAb E-4 per ml were tested in a CI assay with HeLa cells. In performing CI neutralization synergy studies in HeLa cells with MAbs E-4 and E-21, antagonism between MAbs E-4 and E-21 was observed at MAb E-4 concentrations of 10 and 1 micrograms/ml for all concentrations of MAb E-21 tested (10 to 0.1 micrograms/ml). When HaK cells were used in the same studies, no antagonism between the MAbs was found. In addition, when HeLa cells were used in a CI assay, polyclonal serum raised to a peptide representing variable domain IV of the major outer membrane protein inhibited the neutralizing ability of MAb E-21. The blocking of neutralization and the enhancement of infectivity by chlamydia-specific antibodies seen in this investigation with HeLa cells may have important clinical implications for developing preventive strategies for chlamydial infections.
单克隆抗体（MAb）E-4、E-21和DIII A3识别沙眼衣原体主要外膜蛋白可变结构域IV中的相同或相似重叠肽段，但同种型不同，用于非补体依赖（CI）体外中和试验。这些单克隆抗体先前已在补体依赖试验中显示能中和HeLa 229细胞中的衣原体感染性。在本报告中，所有三种单克隆抗体在CI试验中均能中和HaK细胞中的衣原体感染性。然而，当使用HeLa细胞作为宿主细胞时，单克隆抗体E-4（免疫球蛋白G2b [IgG2b]）和单克隆抗体DIII A3（IgG2b）未能中和感染性，而单克隆抗体E-21（IgG1）能中和衣原体感染性。这些发现与以下观点一致：由于存在FcγRIII受体，HeLa细胞促进感染性，从而通过摄取IgG2b-衣原体复合物来阻断中和作用。由于FcγRIII受体不与IgG1结合或结合不良，单克隆抗体E-21在HeLa细胞中对沙眼衣原体的中和作用也证实了FcγRIII受体在这种相互作用中的作用。当在HeLa细胞的CI试验中测试每毫升10微克和1微克的单克隆抗体E-4时，感染性增强了五倍。在用单克隆抗体E-4和E-21对HeLa细胞进行CI中和协同研究时，对于所有测试的单克隆抗体E-21浓度（10至0.1微克/毫升），在单克隆抗体E-4浓度为10微克/毫升和1微克/毫升时观察到单克隆抗体E-4和E-21之间存在拮抗作用。当在相同研究中使用HaK细胞时，未发现单克隆抗体之间存在拮抗作用。此外，当在CI试验中使用HeLa细胞时，针对代表主要外膜蛋白可变结构域IV的肽段产生的多克隆血清抑制了单克隆抗体E-21的中和能力。在本研究中用HeLa细胞观察到的衣原体特异性抗体对中和作用的阻断和感染性的增强，可能对制定衣原体感染的预防策略具有重要的临床意义。
