Ongoing research focuses on the exploration of pathologic inflammatory responses to acute respiratory virus infection and the use of this information to develop creative strategies to circumvent these lethal sequelae characteristic of this disease. We report on two primary studies and a third collaborative work: The first study explored the innate immune responses to pneumonia virus of mice, and generated the intriguing and provocative result that depletion of alveolar macrophages actually prolongs survival in response to acute pneumovirus infection. Specifically, we examined the role of alveolar macrophages in acute infection with pneumonia virus of mice (PVM), a rodent pneumovirus that replicates the clinical sequelae of severe human respiratory syncytial virus disease. We show that PVM replicates in primary mouse macrophage culture, releasing infectious virions and proinflammatory cytokines. Alveolar macrophages isolated from PVM-infected mice express activation markers Clec43 and CD86, cytokines TNF, IL-1, IL-6, and numerous CC and CXC chemokines. Alveolar macrophage depletion prior to PVM infection results in small but statistically significant increases in virus recovery but paradoxically prolonged survival. In parallel, macrophage depleted PVM-infected mice exhibit enhanced NK cell recruitment and increased production of IFNgamma by NK, CD4(+) and CD8(+) T cells. These results suggest an immunomodulatory role for IFNgamma, as overproduction secondary to macrophage depletion may promote survival despite increased virus recovery. Our second featured study follows up on an earlier publication in which we showed that wild-type mice primed via intranasal inoculation with live or heat-inactivated Lactobacillus species (L. plantarum or L. reuteri) were fully (100%) protected against the lethal sequelae of infection with the virulent pathogen, pneumonia virus of mice (PVM), a response that included diminished expression of proinflammatory cytokines and diminished virus recovery. This antiviral property was sustained for as long as 3 - 5 months after lactobacillus priming. This robust and sustained resistance to virus infection resulting from prior interaction with an otherwise unrelated microbe is an example of heterologous immunity. We undertook the present study in order to understand the nature and unique features of this response. Among these features, intranasal inoculation with L. reuteri elicited rapid, transient neutrophil recruitment to the lung tissue in association with numerous proinflammatory mediators (CXCL1, CCL3, CCL2, CXCL10 and TNF). Live L. reuteri was detected in lung tissue but likewise underwent rapid clearance, and was undetectable at 24 hrs after inoculation. In contrast, L. reuteri peptidoglycan (PGN) and L. reuteri genomic DNA (gDNA) remained prominent at 24 and 48 hours after inoculation, respectively. In contrast to live bacteria, intranasal inoculation with isolated L. reuteri gDNA elicited no neutrophil recruitment and no protection against PVM infection;isolated PGN elicited cytokine production and neutrophil recruitment but did not promote sustained survival in response to subsequent PVM infection. Overall, further evaluation of the responses leading to Lactobacillus-mediated heterologous immunity may provide insight into novel antiviral preventive modalities. I contributed to a third study in collaboration with Dr. Joseph B. Domachowske, Professor of Pediatrics, Microbiology and Immunology at SUNY Upstate Medical Center, Syracuse NY which focuses on our shared interests in the pathogenesis of respiratory virus infection. The object was to determine the frequency and effects of nosocomial respiratory viral infections (RVIs) in premature neonates, with a particular focus on those who may be asymptomatic or atypically symptomatic, and thus not recognized as ill. The nursing staff in Syracuse performed a year-long surveillance for respiratory viral infections (RVIs) in all infants <33 weeks gestational age admitted to each of the two regional neonatal intensive care units. Infants were enrolled within 3 days of neonatal intensive care unit admission and were sampled for RVIs until discharge using a multiplex polymerase chain reaction assay capable of detecting 17 different respiratory viruses or subtypes. Among the results, twenty-six (26) of 50 prematurely born infants (52%) tested positive for a respiratory virus, many without clear respiratory indicators, at least once during their birth hospitalization. Testing positive for a respiratory virus was significantly associated with longer length of hospital stay (70 days vs 35 days, P = .002) and prolonged ventilatory support (51 vs 13 days, P = .002). Infants who tested positive for a respiratory virus during their birth hospitalization had more than twice the rate of developing bronchopulmonary dysplasia (BPD;P <.05). Clearly, nosocomial RVIs were frequent in our study population, despite, most interestingly, the absence of clinical indicators of illness. Length of hospital stay was significantly longer and a diagnosis of bronchopulmonary dysplasia was more common in infants who tested positive for respiratory virus using these multiplex assay kits. This finding has extraordinarily broad implications for ongoing management within neonatal ICUs. Reference: Bennett NJ et al. (2012) Unrecognized Viral Respiratory Tract Infections in Premature Infants during their Birth Hospitalization: A Prospective Surveillance Study in Two Neonatal Intensive Care Units. J. Peds, in press
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