de Haan L, Holtrop M, Verweij W R, Agsteribbe E, Wilschut J
Department of Physiological Chemistry Groningen Institute for Drug Studies (GIDS), University of Groningen, The Netherlands.
Vaccine. 1996 Mar;14(4):260-6. doi: 10.1016/0264-410x(95)00235-s.
The Escherichia coli heat-labile enterotoxin (LT) is a potent mucosal immunogen, inducing high secretory as well as systemic antibody responses upon oral or intranasal (i.n.) administration. In addition, LT has the capacity to act as an adjuvant in antibody responses against coadministered other antigens. To investigate the role of the individual subunits of LT in the mucosal immunogenicity and adjuvanticity of LT, the LT holotoxin and the non-toxic B subunit (LTB) were cloned separately and purified from overproducing E. coli cultures. Mice were immunized i.n. with the recombinant LT, LTB and combinations of the two and the induction of LTB-specific serum IgG and IgA as well as mucosal S-IgA was monitored. Intranasal administration of 2 micrograms LTB by itself induced a moderate systemic and a low mucosal antibody response, the latter being restricted to the site of immunization. However, addition of a trace amount (50 ng) of LT holotoxin to LTB strongly stimulated both serum antibody and mucosal S-IgA responses to LTB: the antibody levels induced by 2 micrograms LTB supplemented with 50 ng LT were similar to those seen after immunization with 2.9 micrograms of the LT holotoxin alone (representing an amount of 2 micrograms LTB). Furthermore, immunization with LT-supplemented LTB or with LT holotoxin alone, but not immunization with LTB alone, induced an S-IgA response in distant mucosal tissues including the lung, intestine and the urogenital system. Nicking of the LTA chain with trypsin did not enhance the immunogenicity of LT. These results indicate that, although the LTA chain plays an important role in the mucosal immunogenicity of LT including priming of the common mucosal immune system, extremely low amounts of the LT holotoxin suffice for the induction of high antibody responses to LTB, the trace LT and LTB acting in a synergistic fashion.
大肠杆菌不耐热肠毒素（LT）是一种强效的黏膜免疫原，经口服或鼻内（i.n.）给药后可诱导强烈的分泌性抗体反应以及全身性抗体反应。此外，LT能够作为针对共同给药的其他抗原的抗体反应中的佐剂。为了研究LT各个亚基在LT的黏膜免疫原性和佐剂活性中的作用，分别克隆了LT全毒素和无毒B亚基（LTB），并从过量表达的大肠杆菌培养物中进行纯化。用重组LT、LTB以及二者的组合对小鼠进行鼻内免疫，并监测LTB特异性血清IgG和IgA以及黏膜sIgA的诱导情况。单独鼻内给予2微克LTB可诱导中等程度的全身性抗体反应和较低的黏膜抗体反应，后者局限于免疫部位。然而，向LTB中添加微量（50纳克）的LT全毒素可强烈刺激血清抗体和黏膜sIgA对LTB的反应：2微克LTB补充50纳克LT所诱导的抗体水平与单独用2.9微克LT全毒素免疫后所见的抗体水平相似（相当于2微克LTB的量）。此外，用补充了LT的LTB或单独用LT全毒素免疫，但单独用LTB免疫则不会，可在包括肺、肠道和泌尿生殖系统在内的远处黏膜组织中诱导sIgA反应。用胰蛋白酶切割LTA链并不会增强LT的免疫原性。这些结果表明，尽管LTA链在LT的黏膜免疫原性中发挥重要作用，包括启动共同黏膜免疫系统，但极低量的LT全毒素就足以诱导对LTB的高抗体反应，微量的LT和LTB以协同方式发挥作用。
