Psychosocial stress modulation of the murine anti-viral immune response during a primary influenza infection and the impact on immunologic memory

Complex interactions mediate the immunological response to social stress. Direct connections between the nervous, endocrine and immune systems allow stress-induced neuroendocrine mediators to influence the immune system. Current knowledge regarding mechanisms by which an environmental interaction, such as social defeat, alters the development of adaptive immunity and immunological memory is incomplete. Work in non-chronic stress models has demonstrated activation of the innate immune system, including Langerhans cells, macrophages and dendritic cells (DCs), however less attention has been directed toward regulation of the adaptive immune system. Repeated social defeat (SDR) is a well-characterized model of non-chronic social stress in male mice that induces a number of specific immunological changes, including splenic enlargement due to an influx of immature monocytes and the induction of functional glucocorticoid resistance in monocytes and DCs. In SDR mice, increased pro-inflammatory cytokine levels, including IL-6 and TNF-alpha, have been observed upon toll-like receptor (TLR) engagement of splenocytes. We hypothesized that activation of the cells of the innate immune system, in combination with the pro-inflammatory phenotype induced by SDR, would augment the adaptive immune response to a pathogenic challenge, influenza virus. Furthermore, because patterning of immunological memory is established by the immune response to a primary infection, we hypothesized that alterations induced during a primary response would lead to enhancement of immunological memory. The first part of this study examined SDR-induced changes in immunological memory parameters with a focus on the CD8 +T cell. The second part of this study was designed to investigate potential mechanisms for memory enhancement during a primary influenza viral infection.;Primary Infection. Male C57BL/6 mice underwent SDR or were undisturbed (infected, INF) before intra-nasal infection with 1 hemeagglutinating unit (HAU) of influenza A/PR/8/34. Daily two-hour SDR cycles entailed introduction of an aggressive mouse that defeated all resident mice. Mice were infected after the sixth (final) cycle. Cells were assessed via flow cytometry using fluorescent-labeled antibodies and peptide-specific MHC I tetramers to phenotype immunodominant DbNP366 and DbPA 224 CD8+T cell responses.;Exposure to SDR in the absence of influenza infection increased lung mRNA expression of IFNgamma, which persisted until the cessation of the primary infection. Following infection, SDR mice had an increased number of lung NP366-74CD8+T cells (p<0.05). The influx originated during the clonal expansion phase, and at day 9 post-infection included more cells expressing an activated phenotype: CD25+/CD62L LO NP366-74CD8+ in SDR mice compared with the INF group. No significant changes were noted between groups in the lung PA224CD8+T cell population, however a significant increase in this population was noted at day 8 post-infection only in the spleens of SDR-INF mice. Interestingly, the preferential stimulation of the NP366CD8 +T cell population in SDR-INF mice inverted the conventional NP:PA immunodominance hierarchy in spleen and lung tissue. Predictably in conjunction with the influx of lung CD8+T cells, viral replication in lung tissue of SDR mice was consistently decreased when compared to INF mice.;Memory Responses. The same stress and primary infection protocol were used for all studies. After 6 weeks, resting memory parameters were examined in stressed (SDR-MEM) and non-stressed (MEM) memory mice without additional exposure to the stressor. SDR-MEM mice responded with an enhanced footpad delayed-type hypersensitivity (DTH) response to A/PR/8/34 virus during resting memory. SDR-MEM mice had a significantly enlarged population of CD8 +T cells specific for the immunodominant NP366-74 epitope of A/PR/8/34 virus in lung and spleen tissues during resting memory, and an increase in the CD127HINP366-74CD8+ memory T cell population that was limited to the lung parenchyma. The SDR-MEM lung-derived DbNP366-74CD8+ T cells produced more IFN-gamma upon peptide stimulation during resting memory compared to non-stressed MEM controls. When mice were re-challenged with a 16 HAU dose of A/PR/8 virus, SDR-MEM mice terminated viral replication significantly earlier than non-stressed MEM mice, and generated a larger DbNP366-74CD8 + T cell response in the lung parenchyma and airways.;In the work presented in this dissertation, the experience of repeated social defeat prior to a primary influenza viral infection significantly enhanced the clonal expansion and function of the virus-specific T cell memory pool. Enhanced memory was associated with an altered cytokine milieu in the lung prior to and after primary viral infection and increased expansion of antigen-specific CD8+T cells during the primary and secondary anti-viral responses. Early modification of the lung micro-environment by SDR may have contributed to T cell activation and more rapid clearance of virus from lung tissue in SDR mice. Understanding the mechanisms of SDR-induced stimulation of the virus-specific CD8+T cell response are important, both for further characterization of the nature of the CD8+T cell, and for work in the development of a T-cell-mediated influenza vaccine. Social stressors should be carefully considered in the design and analysis of future studies on anti-viral immunity.