Mechanisms of IgA-mediated immunity to Salmonella

 描述(由申请人提供)：伤寒沙门氏菌(ST)是美国胃肠炎的主要原因，也是撒哈拉以南非洲侵袭性非伤寒沙门氏菌的新兴原因。这项建议将研究肠道分泌物中含量最丰富的一类抗体IgA阻止ST侵袭肠道上皮细胞的机制。在初步研究中，我们已经证明，一种被称为SAL4的针对ST的O5抗原的单抗不仅能保护小鼠免受粘膜ST的感染，而且在体外也能减弱ST的毒力，而不会影响细胞的存活或生长。基于这些和其他结果，我们假设SAL4使O-抗原交联会触发外膜应激反应，从而促进ST从侵袭性状态向非侵袭性状态的转变。然而，在开始对SAL4及其对ST毒力的影响进行更详细的机制研究之前，需要额外的抗O抗原的IgA单抗。SAL4识别ST的O抗原上至少六个不同的抗原决定簇中的一个。目前尚不清楚针对其他O抗原决定簇的IgA抗体是否具有保护性或能够抑制ST的毒力。因此，目标1是产生一组针对STO抗原上不同抗原决定簇的IgA单抗，并测试这些单抗被动保护小鼠免受胃内ST感染的能力。在目标2中，我们将利用已建立的测定细菌运动、肠上皮细胞侵袭和胞外多糖产生的方法，鉴定目标1中鉴定的IgA单抗在体外减弱ST毒力的能力。这些实验将为更详细的机制研究奠定基础，旨在了解分泌抗体如何保护肠道粘膜免受ST感染。

 DESCRIPTION (provided by applicant): Salmonella enterica serovar Typhimurium (ST) is a leading cause of gastroenteritis in the United States and an emerging cause of invasive non-typhoidal salmonella in sub-Saharan Africa. This proposal will investigate the mechanisms by which IgA, the most abundant class of antibody in intestinal secretions, prevents ST from invading intestinal epithelial cells. In preliminary studies, we have demonstrated that a monoclonal IgA antibody (mAb) known as Sal4, which is specific for ST's O5-antigen, not only protects mice from mucosal ST infection, but it also attenuates ST virulence in vitro, without impacting cell viability or growth. Based on these and other results we hypothesize that cross-linking of the O-antigen by Sal4 triggers an outer membrane stress response that promotes the transition of ST from an invasive state to a non-invasive. However, before embarking on a more detailed mechanistic study of Sal4 and its influence on ST virulence, additional IgA mAbs against the O-antigen are required. Sal4 recognizes one of at least six different antigenic determinants on the ST's O-antigen. It is not known whether IgA antibodies against other O-antigenic determinants are protective or capable of suppressing ST virulence. Thus, Aim 1 is to generate a collection of IgA mAbs directed against distinct antigenic determinants on the ST O-antigen and test these mAbs for the ability to passively protect mice against intragastric ST infection. In Aim 2 we will characterize the IgA mAbs identified in Aim 1 for their abilities to attenuate ST virulence in vitro, using established assays that measure bacterial motility, invasion of intestinal epithelial cells, and exopolysaccharide production. These experiments will lay the groundwork for more detailed mechanistic studies aimed at understanding how secretory antibodies protect the intestinal mucosa against ST infection.