Defense mechanisms in Peyer's patches and mesenteric lymph nodes against Yersinia enterocolitica involve integrins and cytokines.

Adhesion molecules and cytokines are involved in regulation of cellular host responses in infection processes. In this study the roles of the integrins Mac-1 and VLA-4, as well as those of the cytokines tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma), in defense mechanisms against Yersinia enterocolitica in Peyer's patches (PP) and mesenteric lymph nodes (MLN) were investigated by blocking these molecules with antibodies in vivo prior to orogastric Yersinia infection. Intestinal Yersinia infection caused abscesses composed of polymorphonuclear (Mac-1+ VLA-4+ Pgp-1+ ICAM-1-) and mononuclear (Mac-1+ VLA-4+ Pgp-1+ ICAM-inhibited phagocytosis of yersiniae by macrophages, (ii) reduced Yersinia-specific proliferation and IFN-gamma production of T cells from PP and MLN, and (iii) caused increased bacterial growth in PP and MLN followed by profound tissue destruction. Neutralization of TNF-alpha or IFN-gamma had comparable effects, suggesting that cell-mediated host responses including activated macrophages are required for control of yersiniae in intestinal tissues. The number of Mac-1+ cells in PP and MLN increased after yersinia infection, and recruitment of these cells was not blocked by administration of anticytokine or anti-integrin antibodies. While anti-VLA-4, -TNF-alpha, or -IFN-gamma antibody treatment caused an increased dissemination of yersiniae from PP to the spleen systemic dissemination was reduced by anti-Mac-1 antibodies. The results of this study suggest that the cytokines IFN-gamma and TNF-alpha as well as the integrins Mac-1 and VLA-4 are involved in protective cellular host defense mechanisms in PP and MLN against Y. enterocolitica, the latter probably being involved in both cell-cell and cell-pathogen interactions.