The purinoreceptor P2X7 is expressed on subsets of T cells and mediates responses of these cells to extracellular nucleotides such as ATP or NAD(+). We identified P2X7 as a molecule highly up-regulated on conventional CD8alphabeta(+) and unconventional CD8alphaalpha(+) T cells of the intestinal epithelium of mice. In contrast, CD8(+) T cells derived from spleen, mesenteric lymph nodes, and liver expressed only marginal levels of P2X7. However, P2X7 was highly up-regulated on CD8(+) T cells from spleen and lymph nodes when T cells were activated in the presence of retinoic acid. High P2X7 expression on intestinal CD8(+) T cells as well as on CD8(+) T cells incubated with retinoic acid resulted in enhanced sensitivity of cells to extracellular nucleotides. Both cell populations showed a high level of apoptosis following incubation with NAD(+) and the ATP derivative 2',3'-O-(benzoyl-4-benzoyl)-ATP, and injection of NAD(+) caused selective in vivo depletion of intestinal CD8(+) T cells. Following oral infection with Listeria monocytogenes, P2X7-deficient mice showed similar CD8(+) T cell responses in the spleen, but enhanced responses in the intestinal mucosa, when compared with similarly treated wild-type control mice. Overall, our observations define P2X7 as a new regulatory element in the control of CD8(+) T cell responses in the intestinal mucosa.

The inhibitor of apoptosis protein (IAP) family has been implicated in immune regulation, but the mechanisms by which IAP proteins contribute to immunity are incompletely understood. We show here that X-linked IAP (XIAP) is required for innate immune control of Listeria monocytogenes infection. Mice deficient in XIAP had a higher bacterial burden 48 h after infection than wild-type littermates, and exhibited substantially decreased survival. XIAP enhanced NF-κB activation upon L. monocytogenes infection of activated macrophages, and prolonged phosphorylation of Jun N-terminal kinase (JNK) specifically in response to cytosolic bacteria. Additionally, XIAP promoted maximal production of pro-inflammatory cytokines upon bacterial infection in vitro or in vivo, or in response to combined treatment with NOD2 and TLR2 ligands. Together, our data suggest that XIAP regulates innate immune responses to L. monocytogenes infection by potentiating synergy between Toll-like receptors (TLRs) and Nod-like receptors (NLRs) through activation of JNK- and NF-κB–dependent signaling.

naofumi takemoto, et al. J Immunol. 2006 Dec 1;177(11):7515-9

An unbiased genetic screen of Listeria monocytogenes mutants that induced an enhanced or diminished host innate immune response showed that the major facilitator superfamily of bacterial multidrug resistance transporters (MDRs) controlled the magnitude of a host cytosolic surveillance pathway, leading to the production of several cytokines. This study may provide insight into the role of the cytosolic surveillance pathway in linking innate and adaptive immunity, thereby leading to the development of adjuvants and vaccines and, perhaps, to the discovery of new therapeutics.

Infected epithelial cells, which act as a first barrier against pathogens, seldom undergo apoptosis. Rather, infected epithelial cells undergo a slow cell death that displays hallmarks of necrosis. Here, we demonstrate that rapid intracellular lysis of Shigella flexneri, provoked by either the use of a diaminopimelic acid auxotroph mutant or treatment of infected cells with antibiotics of the β-lactam family, resulted in a massive and rapid induction of apoptotic cell death. This intracellular bacteriolysis-mediated apoptotic death (IBAD) was characterized by the specific involvement of the mitochondrial-dependent cytochrome c/Apaf-1 axis that resulted in the activation of caspases-3, -6 and -9. Importantly, Bcl-2 family members and the NF-κB pathway seemed to be critical modulators of IBAD. Finally, we identified that IBAD was also triggered by Salmonella enterica serovar Typhimurium but not by the Gram-positive bacteria, Listeria monocytogenes. Together, our results demonstrate that, contrary to previous findings, epithelial cells are intrinsically able to mount an efficient apoptotic cell death response following infection. Indeed, apoptosis in normal circumstances is masked by powerful anti-apoptotic mechanisms, which are overcome in IBAD. Our results also uncover an unexpected consequence of the treatment of infected cells with certain classes of antibiotics.

Alors qu'il ne cessait de diminuer depuis vingt ans, le nombre de cas de listériose diagnostiqués en France a brusquement augmenté à partir de 2006, cette inversion de tendance se confirmant en 2007, sans qu'on en connaisse l'origine. Telle est la conclusion d'une étude publiée dans le Bulletin épidémiologique hebdomadaire de l'Institut de veille sanitaire (InVS) du mardi 22 juillet. "Le nombre de cas de listériose avait été divisé par trois entre 1987 et 1997, rappelle Véronique Goulet (InVS). L'incidence a diminué jusqu'en 2001, puis s'est stabilisée jusqu'en 2005. Or cette tendance s'est depuis inversée." On est ainsi passé de 221 cas en 2005, à 290 en 2006, et à 319 en 2007. On estime entre 20 % et 30 % la proportion de ceux qui ont été mortels. Cette recrudescence concerne plus particulièrement les personnes âgées de plus de 60 ans ainsi que les personnes immunodéprimées et celles souffrant de certains cancers. Les mêmes tendances ont été observées, depuis 1999, dans différents pays européens, dont l'Allemagne, l'Espagne et le Royaume-Uni.

The Listeria monocytogenes protein listeriolysin O (LLO) is a pore-forming protein essential for virulence. Although the major role for LLO is to allow L. monocytogenes entry into the cytosol, it also induces apoptosis of activated lymphocytes, an obligatory cellular response that modulates the infection. Induction of apoptosis by LLO proceeds through a fast, caspase-dependent pathway and a slow, caspase-independent pathway. Polyclonal T cell lines were generated from either normal mice or mice deficient in granzyme and perforin proteins, and then treated with apoptogenic doses of LLO. In this study we show that apoptosis of lymphocytes induced by LLO was characterized by activation of caspases as quickly as 30 min that was dependent on the expression of granzymes. In the absence of granzymes, all parameters of apoptosis such as caspase activation, phosphatidylserine exposure, mitochondrial depolarization, and DNA fragmentation were dramatically reduced in magnitude. Removal of perforin inhibited the apoptotic effect of LLO on cells by approximately 50%. Neutralization of intracellular acidification using chloroquine inhibited the rapid apoptotic death. In agreement with these findings granzyme-deficient mice harbored lower bacterial titers and decrease splenic pathology compared with normal mice following L. monocytogenes infection. Thus, LLO exploits apoptotic enzymes of the adaptive immune response to eliminate immune cells and increase its virulence.