Elson C O, Solomon S
Department of Medicine, University of Alabama, Birmingham 35294.
Infect Immun. 1990 Nov;58(11):3711-6. doi: 10.1128/iai.58.11.3711-3716.1990.
Cholera toxin (CT) and its B subunit (CT-B) are potent oral immunogens in vivo, although both strongly inhibit polyclonal lymphocyte activation in vitro. In order to help understand this paradox, we have studied the activation and proliferation of CT-specific T cells in vitro, by using CT-B-primed lymph node T cells as responders, concanavalin A-stimulated peritoneal macrophages as antigen-presenting cells (APCs), and various forms of CT-B as antigen. The results indicate that in many ways CT-specific T cells respond in a manner similar to that of T cells specific for other protein antigens: the degree of proliferation was proportional to the dose of antigen and APCs in the cultures, was antigen specific, and was H-2 restricted. APCs from genetic high-responder strains to CT stimulated significantly more proliferation in F1 (high x low) responder T cells than did APCs from low responder strains. However, there was a marked difference in the activation of CT-specific T cells when different forms of CT-B were used. Native CT-B stimulated little or no T-cell proliferation, whereas denatured CT-B or CT-B blocked by its ligand, GM1 ganglioside, stimulated T cells well. Addition of native CT-B to cocultures of primed T cells, APCs, and these latter stimulatory forms of CT-B inhibited the specific proliferative response to CT-B to varying degrees, depending on the ratio of the two forms in culture. We conclude that the ability of CT-B to inhibit T cells extends even to T cells specific for CT itself. Because of these inhibitory properties, processing of CT to nonbinding molecular forms or fragments must be an important prerequisite for the immune response to CT to occur in vivo, and such processing is likely to be important in the immune response to a variety of other enterotoxins as well.
霍乱毒素（CT）及其B亚基（CT-B）在体内是有效的口服免疫原，尽管两者在体外均强烈抑制多克隆淋巴细胞活化。为了有助于理解这一矛盾现象，我们通过使用经CT-B致敏的淋巴结T细胞作为应答细胞、伴刀豆球蛋白A刺激的腹腔巨噬细胞作为抗原呈递细胞（APC）以及各种形式的CT-B作为抗原，研究了体外CT特异性T细胞的活化和增殖。结果表明，在许多方面，CT特异性T细胞的反应方式与其他蛋白质抗原特异性T细胞相似：增殖程度与培养物中抗原和APC的剂量成正比，具有抗原特异性，并且受H-2限制。来自对CT基因高反应性品系的APC比来自低反应性品系的APC在F1（高×低）反应性T细胞中刺激的增殖明显更多。然而，当使用不同形式的CT-B时，CT特异性T细胞的活化存在显著差异。天然CT-B刺激很少或不刺激T细胞增殖，而变性CT-B或被其配体GM1神经节苷脂阻断的CT-B能很好地刺激T细胞。将天然CT-B添加到致敏T细胞、APC和这些后一种刺激性形式的CT-B的共培养物中，根据培养物中两种形式的比例，会在不同程度上抑制对CT-B的特异性增殖反应。我们得出结论，CT-B抑制T细胞的能力甚至延伸到对CT本身特异性的T细胞。由于这些抑制特性，将CT加工成非结合分子形式或片段必定是体内对CT发生免疫反应的重要先决条件，并且这种加工在对多种其他肠毒素的免疫反应中可能也很重要。
