Lines show the mean antibody activity in each immunized group. Antigen-nave Balb/c mice survive intranasal challenge with 102cfuFtLVS but succumb within 7 d to intranasal inoculation with 103cfuFtLVS. 10In the current study, mice sensitized with 200 cfuFtLVS were challenged 7 wk later with 2 . 6 107cfuFtLVS and monitored daily for morbidity and mortality. few studies have addressed the effect of ambient heat on protective immunity in mice. Guidelines from the United States National Institutes of Wellness dictate that mice should be housed at 20 to 26 C. 15However, to maintain a core temperature of approximately 37 C, mice begin to produce additional body heat when the ambient heat drops below approximately 30 C. Studies on thermal physiology have established that the thermoneutral zone (TNZ) of various mouse strains is 30 to 32 C, the heat range of minimal metabolic energy expenditure. 11, 13The discrepancy between standard vivarium housing temperatures and the mouse TNZ has mainly been overlooked by the study community and regulatory agencies but may have profound implications in the translation of mouse models to human being disease. Chronic cold stress results in production and recruitment of brown adipose tissue for adaptive thermogenesis, due to norepinephrine release from Defactinib the sympathetic nervous system. 4This then may result in corticosteroid release from the adrenal cortex, which engages -adrenergic receptors on many immune cells. 26Consequently, global suppression of the immune system may occur, particularly of proinflammatory cells involved in immune protection8as well as the expansion of immunosuppressive M2 macrophages. 25Suppressed immune responses due to chilly stress in mice housed below their lower critical temperature may account for the high mouse mortality in and failure of numerous mouse models of bacterial, viral, and protozoal infections. 19 Several recent studies are consistent with this hypothesis. Mice inoculated intraperitoneally withKlebsiella pneumoniaand housed at 34 C displayed as much as a 105-fold reduce bacterial load18and a 400-fold lower pulmonary pathogen burden after intratracheal inoculation28than control infected mice maintained at 23 C. In a pulmonary influenza computer virus infection model, mice managed at SLC7A7 30 C avoided excessive production of proinflammatory cytokines in lung tissue compared with mice maintained at 22 C or 26 C. 16 Defactinib Although these results suggest that better immune protection occurs in the absence of cold stress, these studies were all short-term (3 to 7 d), so only innate immune responses would likely be engaged. In addition , with the exception of one study, 18survival did not improve at elevated ambient temperatures, possibly due to collateral inflammation-mediated damage from a robust immune response. In a recent study of immunity to solid tumors, mice managed at 31 C developed increased numbers of tumor-infiltrating CD8+T cells, reduced tumor volume, and increased survival compared with mice housed at 23 C, 21suggesting that adaptive immunity is improved when chilly stress is avoided. Qualitatively similar findings were obtained in a graft-versus-host disease mouse model. 23 It is hypothesized that mice commonly fail to mount protective immune responses to infectious agents because of the physiologic effects of cold stress brought on by housing temperatures below the mouse TNZ. Because mice housed well below their TNZ maintain an average core body temperature of 36 to 37. 5 C12, 35due to adaptive thermogenesis, 4the environmental temperatures of Defactinib both the infectious agent and the mediators of protective immunity are essentially the same regardless of the ambient vivarium heat. The current study compares the T- and B-cell responses to an attenuated strain ofFrancisella tularensis(FtLVS) as well as survival to a potentially lethal dose ofFtLVS in mice maintained at typical vivarium temperatures compared with housing within the mouse TNZ. == Materials and Methods == == Mouse husbandry. == Creature housing conditions and experimental design were approved by the IACUC from the University of New Mexico Wellness Sciences Center (Albuquerque, NM) in accordance with the NIH guidelines15and AALAS principles in an AAALAC-accredited SPF facility on a 12: 12-h light: dark cycle. Every 3 to 4 mo, the facility submits blood from sentinel mice maintained in soiled bedding as.