Sequestering of Rac by the Yersinia effector YopO blocks Fcgamma receptor-mediated phagocytosis.

Pathogenic Yersinia species neutralize innate immune mechanisms by injecting type three secretion effectors into immune cells, altering cell signaling. Our study elucidates how one of these effectors, YopO, blocks phagocytosis. We demonstrate using different phagocytic models that YopO specifically blocks Rac-dependent Fcgamma receptor internalization pathway but not complement receptor 3-dependent uptake, which is controlled by Rho activity. We show that YopO prevents Rac activation but does not affect Rac accumulation at the phagocytic cup. In addition, we show that plasma membrane localization and the guanine-nucleotide dissociation inhibitor (GDI)-like domain of YopO cooperate for maximal anti-phagocytosis. Although YopO has the same affinity for Rac1, Rac2, and RhoA in vitro, it selectively interacts with Rac isoforms in cells. This is due to the differential localization of the Rho family G proteins in resting cells; Rac isoforms partially exist as a GDI-free pool at the membrane of resting cells, whereas RhoA is trapped in the cytosol by RhoGDIalpha. We propose that YopO exploits this basic difference in localization and availability to selectively inhibit Rac-dependent phagocytosis.

Mucosal immunity in healthy adults after parenteral vaccination with outer-membrane vesicles from Neisseria meningitidis serogroup B.

BACKGROUND: Nasopharyngeal carriage of meningococcus or related species leads to protective immunity in adolescence or early adulthood. This natural immunity is associated with mucosal and systemic T cell memory. Whether parenteral Neisseria meningitidis serogroup B (MenB) vaccination influences natural mucosal immunity is unknown. OBJECTIVES: To determine whether parenteral MenB vaccination affects mucosal immunity in young adults and whether this immunity differs from that induced in the blood. METHODS: Otherwise healthy volunteers were immunized with MenB outer membrane vesicle vaccine before and after routine tonsillectomy. Mucosal and systemic immunity were assessed in 9 vaccinees and 12 unvaccinated control subjects by measuring mononuclear cell proliferation, cytokine production, Th1/Th2 surface marker expression, and antibody to MenB antigens. RESULTS: Parenteral vaccination induced a marked increase in systemic T cell immunity against MenB and a Th1 bias. In contrast, although mucosal T cell proliferation in response to MenB neither increased nor decreased following vaccination, mononuclear cell interferon gamma, interleukin (IL)-5, and IL-10 production increased, and the Th1/Th2 profile lost its Th1 bias. CONCLUSIONS: Parenteral MenB vaccination selectively reprograms preexisting naturally acquired mucosal immunity. As new-generation protein-based MenB vaccine candidates undergo evaluation, the impact of these vaccines on mucosal immunity in both adults and children will need to be addressed.

Tonsil T cell immunity to human papillomavirus in the absence of detectable virus in healthy adults.

BACKGROUND: Human papillomavirus (HPV) is known to infect the epithelium of the upper aerodigestive tract; however, major questions regarding prevalence and persistence of infection, and their relation to local immune response, remain unanswered. OBJECTIVES: To evaluate the tonsil T cell immune response to HPV and compare this to the frequency of detectable virus at this site. STUDY DESIGN: A cross-sectional study of cancer-free adults undergoing routine tonsillectomy. METHODS: Mucosal immune responses to recombinant HPV16 L2E6E7 and HPV6 L2E7 antigens were measured by tonsillar T-lymphocyte proliferation assay in 13 subjects. HPV deoxyribonucleic acid (DNA) was assessed by PCR and reverse line-blot hybridization in an expanded population of 44 subjects. RESULTS: Proliferative T-cell responses to HPV16 and HPV6 were identified in all patients. The presence of a CD45RO+ T cell population responsive to HPV6 L2E7 was confirmed in three of six subjects tested. There were no CD45RO+ responses to HPV16 L2E6E7 and no evidence of current or latent HPV infection of the tonsil. CONCLUSIONS: T cell memory to human papillomavirus can be identified in tonsil tissue from an adult population in the absence of concurrent HPV infection. How novel HPV vaccines might augment this preexisting cell-mediated immunity is an essential area for investigation.

Regulation of Th-1 T cell-dominated immunity to Neisseria meningitidis within the human mucosa.

Neisseria meningitidis is commonly carried asymptomatically in the upper respiratory tract and only occasionally invades the bloodstream and meninges to cause disease. Naturally acquired immunity appears protective but the nature of the cellular immune response within the mucosa is uncertain. We show that following in vitro stimulation with N. meningitidis serogroup B (MenB) antigens, approximately 66% of the dividing mucosal CD4(+)CD45RO(+) memory population express the Th1-associated IL18-R while the remainder express CRTH2, a Th2-associated marker. The pro-inflammatory bias of this anti-MenB response is not evident in blood, demonstrating compartmentalization at the induction site; and occurs in the presence or absence of lipopolysacharide indicating that these responses are already fully committed. Depletion of CD25(+) cells reveals suppression of the effector CD4(+) T cell response restricted to the mucosa and most marked in children (i.e. those at greatest risk of disease). Mucosal T-regulatory cell (Treg) activity is partially overcome by blocking the human glucocorticoid-induced TNF receptor (GITR) and is not seen following stimulation with antigens from another mucosal pathogen, influenza virus. Pro-inflammatory, antimeningococcal T cell responses may limit invasive disease at the mucosa but Treg induction while reducing immunopathological damage, may also restrict the effectiveness of the protective response, particularly in children.