Project 1. Dr. Xiaohong Lu
Neurodevelopmental disorders characterized by social deficits, e.g., autism and schizophrenia, have long been associated with immune dysfunction. However, largely due to the lack of an etiologically-relevant animal model, the causal evidence needed to link immune dysfunction to neurodevelopmental disorders in humans remains elusive. Several recent large-scale genome-wide association studies (GWAS) pinpointed a Copy Number Variation (CNV) at the chromosomal locus 7q36.6 that is highly represented in schizophrenia and autism1. All of the microduplications (triplications) occur within a single gene: vasoactive intestinal peptide receptor 2 (VIPR2). In lymphocytes from these patients, VIPR2 is overexpressed by two-fold. In children with autism, the VIPR2 ligand, vasoactive intestinal peptide (VIP) is found to be almost three times higher in the blood at birth. Importantly, VIP has been viewed as a Th2-secreted cytokine. Activation of VIP/VIPR2 signaling is well known to shift the Th1/Th2 balance in favor of Th2 cells. To link T cell immune dysfunction to neurodevelopment and social deficits, we generated a Bacterial Artificial Chromosome (BAC) transgenic mouse model of human VIPR2 CNV that allows switching-off of the transgene in desired spatial-temporal patterns, controlled by the Cre recombinase, thus facilitating dissection of the afflicted cell populations. These mice had robust social and cognitive behavioral deficits that were preceded by a disrupted early postnatal brain development, such as delayed microglia maturation. Autism has been associated with an altered Th1/Th2 function that is skewed in favor of a Th2 response. Activation of VIP/VIPR2 signaling in T cells leads to Th2 differentiation, which in turn would inhibit Th1 responses. Cytokines released by Th1, but not Th2 cells, are required to stimulate resident microglia to maturation. Taken together, we argue that overactive Th2 polarization impairs the maturation of microglia and disrupts social brain development, while low levels of Th1 cytokines (e.g., IFN-γ) suppress normal social behavior (see the Figure above for our model). Therefore we hypothesize that VIPR2 overexpression in T cells promotes the Th2 polarization that disrupts early brain development and triggers social behavioral deficits.
Project 2. Dr. Ana Dragoi
The betaproteobacteria Neisseria gonorrhoeae (N.g) is a highly adapted human colonizer and the etiological agent of gonorrhea, a sexually transmitted disease (STD) that has emerged as a major global public health problem. Rising incidence, coupled with prevalent and increasing antibiotics resistance highlights the need to understand better the molecular basis of N.g pathogenesis and the need for new therapeutic targets. N.g mainly colonizes the genital mucosa, but it can also colonize the ocular, nasopharyngeal and anal mucosa. Pathology largely results from the damage caused by the activation of innate immune responses at the sites of bacterial colonization3. Ascending gonococcal infections frequently occur, particularly in women. The most significant morbidity and mortality caused by N.g is due to pelvic inflammatory disease and the post-infection complications associated with scarring of the fallopian tubes. Antibiotic resistance is a substantial problem due to high frequency acquisition of genetic material from the environment. Following the spread of fluoroquinoloneresistant and cephalosporin-resistant N.g there are very few antibiotic options left that are well-studied, well-tolerated and highly effective. The first step in N.g pathogenesis is adherence of bacteria to the host epithelium, a process mediated by type IV pili, opacity (Opa) proteins, lipooligosaccharide (LOS) and the major outer membrane protein porin (also known as PorB). Specifically, the interaction between N.g Opa proteins and the host cell CEACAM (carcinoembryonic antigen-related cell adhesion molecule) family of proteins have been considered crucial for both colonization and immune system evasion. The initial phases of N.g infections and its interactions with mucosal epithelium and neutrophils (PMNs) have been extensively studied. Neutrophils, however, are short-lived cells (~6-8h half-life) and infection with N.g can only briefly delay the onset of PMN6,7 apoptosis. On the other hand, our and other studies show that N.g can strongly replicate and avoid phagocytic killing in macrophages, which allows bacterial growth for more than 24h. Wefurther characterized N.g invasion and cell-to-cell spread in macrophages and uncovered that: (1) N.g replicates and propagates efficiently when in contact with human macrophages; (2) extracellular and intracellular growth are both employed by N.g when infecting macrophages; (3) only a small number of intracellular N.g are targeted to the lysosomes (LAMP2/Rab7 positive) for degradation and (4) actin polymerization is important for N.g infection in macrophages (see Model). Thus, macrophages are an unexplored and potentially essential cellular reservoir for N.g. during infection that can serve as a significant replicative niche in vivo. We hypothesize that N.g colonization and replication within macrophages plays an important role in gonorrhea pathogenesis. Our findings present an opportunity for us to explore macrophage-centered therapies that can be exploited to steer gonorrhea towards outcomes that favor the host. However, determining the mechanisms used by N.g to colonize and replicate in macrophages is critical for this understanding of the pathogenesis of the disease and for the design of new therapies.
Project 3. Dr. Monica Gestal
Despite ongoing efforts to improve vaccines and therapies, the incidence of infectious respiratory diseases (RDs) has been increasing and remains a major cause of morbidity and mortality worldwide. The RD pertussis is on the rise even though an FDA approved vaccine is widely administered. The whole cell vaccine introduced in 1945 drastically decreased the number of whooping cough cases, but due to undesirable side effects was replaced with an acellular vaccine in the 1990’s. The acellular vaccine, though safer, is less effective at blocking colonization and exhibits rapidly waning immunity. Our long-term goal is to use the murine model of Bordetella bronchiseptica to gain mechanistic insights into respiratory immune responses that promote T-cell differentiation and provide durable immunity to RDs. We hope to leverage our findings toward the development of improved vaccines. Eosinophils contribute to gastric immune homeostasis24-31 particularly during helminthic infections. Their potential involvement in the generation of adaptive immune responses in gut infections is gaining attention. However, the underlying mechanism by which eosinophils modulate T cells responses remains unclear. Our data reveal that eosinophil recruitment in the lungs coincides with peak levels of B. bronchiseptica (BB) in lungs of experimentally infected mice and remained high until the infection is cleared, suggesting that eosinophils contribute to clearance of BB from the lower respiratory tract. Mice lacking eosinophils fail to clear BB from the lungs supporting a role for eosinophils in BB clearance. Moreover, they have reduced production of proinflammatory cytokines such as IL-17 and anti-Bordetella antibodies, suggesting that eosinophils promote protective Th17 responses and subsequent antibody production during Bordetella infection. In more general terms, eosinophils may be important for the generation of a protective adaptive immunity during respiratory bacterial infections. Thus, we hypothesize that eosinophils present antigen and promote Th17 T cell responses in the lung during respiratory infections. Understanding how eosinophils modulate adaptive responses may open up new avenues for the development of therapies and more efficacious vaccines by enhancing eosiniphilic activity.