Claire A. Chougnet

Neonatal NK cells target the mouse duct epithelium via Nkg2d and drive tissue-specific injury in experimental biliary atresia

Biliary atresia is a neonatal obstructive cholangiopathy that progresses to end-stage liver disease. Although the etiology is unknown, a neonatal adaptive immune signature has been mechanistically linked to obstruction of the extrahepatic bile ducts. Here, we investigated the role of the innate immune response in the pathogenesis of biliary atresia. Analysis of livers of infants at diagnosis revealed that NK cells populate the vicinity of intrahepatic bile ducts and overexpress several genes involved in cytotoxicity. Using a model of rotavirus-induced biliary atresia in newborn mice, we found that activated NK cells also populated murine livers and were the most abundant cells in extrahepatic bile ducts at the time of obstruction. Rotavirus-primed hepatic NK cells lysed cholangiocytes in a contact- and Nkg2d-dependent fashion. Depletion of NK cells and blockade of Nkg2d each prevented injury of the duct epithelium after rotavirus infection, maintained continuity of duct lumen between the liver and duodenum, and enabled bile flow, despite the presence of virus in the tissue and the overexpression of proinflammatory cytokines. These findings identify NK cells as key initiators of cholangiocyte injury via Nkg2d and demonstrate that injury to the duct epithelium drives the phenotype of experimental biliary atresia.

Chronic Fetal Exposure to Ureaplasma parvum Suppresses Innate Immune Responses in Sheep

The chorioamnionitis associated with preterm delivery is often polymicrobial with ureaplasma being the most common isolate. To evaluate interactions between the different proinflammatory mediators, we hypothesized that ureaplasma exposure would increase fetal responsiveness to LPS. Fetal sheep were given intra-amniotic (IA) injections of media (control) or Ureaplasma parvum serovar 3 either 7 or 70 d before preterm delivery. Another group received an IA injection of Escherichia coli LPS 2 d prior to delivery. To test for interactions, IA U. parvum-exposed animals were challenged with IA LPS and delivered 2 d later. All animals were delivered at 124 ± 1-d gestation (term = 150 d). Compared with the 2-d LPS exposure group, the U. parvum 70 d + LPS group had 1) decreased lung pro- and anti-inflammatory cytokine expression and 2) fewer CD3+ T lymphocytes, CCL2+, myeloperoxidase+, and PU.1+ cells in the lung. Interestingly, exposure to U. parvum for 7 d did not change responses to a subsequent IA LPS challenge, and exposure to IA U. parvum alone induced mild lung inflammation. Exposure to U. parvum increased pulmonary TGF-β1 expression but did not change mRNA expression of either the receptor TLR4 or some of the downstream mediators in the lung. Monocytes from fetal blood and lung isolated from U. parvum 70 d + LPS but not U. parvum 7 d + LPS animals had decreased in vitro responsiveness to LPS. These results are consistent with the novel finding of downregulation of LPS responses by chronic but not acute fetal exposures to U. parvum. The findings increase our understanding of how chorioamnionitis-exposed preterm infants may respond to lung injury and postnatal nosocomial infections.

Myeloid dendritic cells isolated from tissues of SIV-infected Rhesus macaques promote the induction of regulatory T cells.

Objective:To determine whether the ability of primary myeloid dendritic cells (mDCs) to induce regulatory T cells (Treg) is affected by chronic simian immunodeficiency virus (SIV) infection. Design:Modulation of dendritic cell activity with the aim of influencing Treg frequency may lead to new treatment options for HIV and strategies for vaccine development. Methods:Eleven chronically infected SIV+ Rhesus macaques were compared with four uninfected animals. Immature and mature mDCs were isolated from mesenteric lymph nodes and spleen by cell sorting and cultured with purified autologous non-Treg (CD4+CD25− T cells). CD25 and FOXP3 up-regulation was used to assess Treg induction. Results:The frequency of splenic mDC and plasmacytoid dendritic cell was lower in infected animals than in uninfected animals; their frequency in the mesenteric lymph nodes was not significantly altered, but the percentage of mature mDCs was increased in the mesenteric lymph nodes of infected animals. Mature splenic or mesenteric mDCs from infected animals were significantly more efficient at inducing Treg than mDCs from uninfected animals. Mature mDCs from infected macaques induced more conversion than immature mDCs. Splenic mDCs were as efficient as mesenteric mDCs in this context and CD103 expression by mDCs did not appear to influence the level of conversion. Conclusions:Tissue mDCs from SIV-infected animals exhibit an enhanced capability to induce Treg and may contribute to the accumulation of Treg in lymphoid tissues during progressive infection. The activation status of dendritic cell impacts this process but the capacity to induce Treg was not restricted to mucosal dendritic cells in infected animals.

IL-15 Fosters Age-Driven Regulatory T Cell Accrual in the Face of Declining IL-2 Levels.

We and others have shown that regulatory T cells (Treg) accumulate dramatically with age in both humans and mice. Such Treg accrual contributes to age-related immunosenescence as they reduce the response to tumors and parasite infection. While we reported earlier that aged Treg have decreased expression of the pro-apoptotic molecule Bim and germline deletion of Bim promoted earlier accumulation of Treg, it remains unclear whether the effects of Bim are: (i) Treg intrinsic and (ii) dominant to other BH3-only pro-apoptotic molecules. Further, the mechanism(s) controlling Bim expression in aged Treg remain unclear. Here we show that Treg-specific loss of Bim is sufficient to drive Treg accrual with age and that additional loss of the downstream apoptotic effectors Bax and Bak did not exacerbate Treg accumulation. Further, our results demonstrate that a subpopulation of Treg expands with age and is characterized by lower expression of CD25 (IL-2Rα) and Bim. Mechanistically, we found that IL-2 levels decline with age and likely explain the emergence of CD25loBimlo Treg because Treg in IL-2−/− mice are almost entirely comprised of CD25loBimlo cells, and IL-2 neutralization increases CD25loBimlo Treg in both young and middle-aged mice. Interestingly, the Treg population in aged mice had increased expression of CD122 (IL-2/IL-15Rβ) and neutralization or genetic loss of IL-15 led to less Treg accrual with age. Further, the decreased Treg accrual in middle-aged IL-15−/− mice was restored by the additional loss of Bim (IL-15−/−Bim−/−). Together, our data show that aging favors the accrual of CD25lo Treg whose homeostasis is supported by IL-15 as IL-2 levels become limiting. These data have implications for manipulating Treg to improve immune responses in the elderly.

Pulmonary Morbidity in Infancy after Exposure to Chorioamnionitis in Late Preterm Infants

RATIONALEnChorioamnionitis is an important cause of preterm birth, but its impact on postnatal outcomes is understudied.nnnOBJECTIVESnTo evaluate whether fetal exposure to inflammation is associated with adverse pulmonary outcomes at 6 to 12 months chronological age in infants born moderate to late preterm.nnnMETHODSnInfants born between 32 and 36 weeks gestational age were prospectively recruited (Nu2009=u2009184). Chorioamnionitis was diagnosed by placenta and umbilical cord histology. Select cytokines were measured in samples of cord blood. Validated pulmonary questionnaires were administered (nu2009=u2009184), and infant pulmonary function testing was performed (nu2009=u200969) between 6 and 12 months chronological age by the raised volume rapid thoracoabdominal compression technique.nnnMEASUREMENTS AND MAIN RESULTSnA total of 25% of participants had chorioamnionitis. Although infant pulmonary function testing variables were lower in infants born preterm compared with historical normative data for term infants, there were no differences between infants with chorioamnionitis (nu2009=u200920) and those without (nu2009=u200949). Boys and black infants had lower infant pulmonary function testing measurements than girls and white infants, respectively. Chorioamnionitis exposure was associated independently with wheeze (odds ratio [OR], 2.08) and respiratory-related physician visits (OR, 3.18) in the first year of life. Infants exposed to severe chorioamnionitis had increased levels of cord blood IL-6 and greater pulmonary morbidity at age 6 to 12 months than those exposed to mild chorioamnionitis. Elevated IL-6 was associated with significantly more respiratory problems (OR, 3.23).nnnCONCLUSIONSnIn infants born moderate or late preterm, elevated cord blood IL-6 and exposure to histologically identified chorioamnionitis was associated with respiratory morbidity during infancy without significant changes in infant pulmonary function testing measurements. Black compared with white and boy compared with girl infants had lower infant pulmonary function testing measurements and worse pulmonary outcomes.

T Cell Responses During Human Immunodeficiency Virus (HIV)-1 Infection

The defining features of the acquired immunodeficiency are the “xadpersistent and profound selective decrease in the function as well as number of T lymphocytes of the helper/inducer subset and a possible activation of the suppressor/cytotoxic subset”, as described in 1982 (Mildvan, D., U. Mathur, et al. (1982). “Opportunistic infections and immune deficiency in homosexual men.” Ann Intern Med 96(6 Pt 1): 700–4). Nowadays, although depletion of CD4+ T-cells remains a hallmark of Human Immunodeficiency Virus (HIV) infection, the multifactorial nature of the disease provoked by infection by HIV-1 or Simian Immunodeficiency Virus (SIV) in “non-natural” hosts is generally acknowledged, in that no unique immune alteration has been identified that can fully explain the plethora of dysregulation associated with the development of pathogenic HIV and SIV infection.