Effect of orchidectomy on the age-related modulation of IL-1beta and IL-1 receptors following lipopolysaccharide treatment in the mouse

Gonadal hormone-dependent and -independent regulation of immune function by photoperiod in Siberian hamsters

Siberian hamsters (Phodopus sungorus) exhibit changes in reproductive and immune function in response to seasonal variations in day length. Exposure to short days induces gonadal regression and inhibits testosterone secretion. In parallel, short days enhance immune function: increasing leukocyte numbers and attenuating cytokine and behavioral responses to infection. We examined whether photoperiodic changes in leukocyte phenotypes and sickness behaviors are dependent on concurrent photoperiodic changes in gonadal function. Male hamsters were gonadectomized or sham-gonadectomized and either exposed to short days (9 h light/day; SD) or kept in their natal long-day (15 h light/day; LD) photoperiod for 10-13 wk. Blood samples were obtained for leukocyte enumeration, and hamsters were challenged with bacterial LPS, which induced behavioral (anorexia, reductions in nest building) and somatic (weight loss) sickness responses. Among gonad-intact hamsters, exposure to SD increased total and CD62L+ lymphocytes and CD3+ T lymphocytes in blood and significantly attenuated LPS-induced sickness responses. Independent of photoperiod, castration alone increased total and CD62L+ lymphocyte and CD3+ T lymphocyte numbers and attenuated somatic and anorexic sickness responses. Among castrated hamsters, SD exposure increased lymphocyte numbers and suppressed sickness behaviors. In castrated hamsters, the magnitude of most immunological effects of SD were diminished relative to those evident in gonad-intact hamsters. The SD phenotype in several measures of immunity can be instated via elimination of gonadal hormones alone; however, photoperiodic effects on immune function persist even in castrated hamsters. Thus, photoperiod affects the immune system and neural-immune interactions underlying sickness behaviors via gonadal hormone-dependent and -independent mechanisms.

eae36, a locus on mouse chromosome 4, controls susceptibility to experimental allergic encephalomyelitis in older mice and mice immunized in the winter

Genetic factors are believed to contribute to multiple sclerosis (MS) susceptibility; however, strong evidence implicating intrinsic and environmental factors in the etiopathogenesis of MS also exists. Susceptibility to experimental allergic encephalomyelitis (EAE), the principal animal model of MS, is also influenced by nongenetic factors, including age and season at immunization. This suggests that age- and season-by-gene interactions exist and that different susceptibility loci may influence disease as a function of the two parameters. In this study, linkage analysis based on genome exclusion mapping was carried out using age and season at immunization restricted cohorts of (B10.S x SJL/J) F2 intercross mice in an effort to identify such linkages. Significant linkage of EAE to eae4 and eae5 was detected with 6- to 12-week-old and summer cohorts. In contrast, significant linkage of EAE to eae4 and eae5 was not detected with the >12-week-old and winter/spring populations. Rather, significant linkage to D4Mit203 at 128.50 Mb on chromosome 4 was detected with animals that were >12 weeks old at the time of immunization or were immunized in the winter. This previously unidentified locus has been designated eae36. These results support the existence of age- and season-by-gene-specific interactions in the genetic control of susceptibility to autoimmune inflammatory disease of the central nervous system and suggest that late-onset MS may be immunogenetically distinct.

Immune response gene expression increases in the aging murine hippocampus

Using GeneChips, basal and lipopolysaccharide (LPS)-induced gene expression was examined in the hippocampus of 3-, 12-, 18- and 24-month-old male C57BL/6 mice to identify genes whose altered expression could influence hippocampal function in advanced age. Gene elements that changed with age were selected with a t-statistic and specific expression patterns were confirmed with real-time quantitative PCR. Basal expression of 128 gene elements clearly changed with age in the hippocampus. Fourteen gene elements showed increased expression with age and these increases were validated after LPS stimulation. Major histocompatibility complex (MHC) TL region and thymic shared antigen (TSA-1) gene expression increased, suggesting T cell activation in the hippocampus with age. Cytokine (interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha) and chemokine (macrophage chemotactic protein-1) expression increased sharply in 24-month-old mice. These findings are in contrast to a decrease in the peripheral immune response, documented by decreased T cell proliferation and decreased ratios of naive to memory T cells. Age-related increases in inflammatory potential in the brain may contribute to neurodegenerative diseases of the aged.

Sexual dimorphism in the pituitary-adrenal response to tumor necrosis factor-alpha, but not to interleukin-6, in the rat

It is known that the pituitary-adrenal responses to lipopolysaccharide and interleukin (IL)-1 are sexually dimorphic in rodents, with females having an enhanced secretion of adrenocorticotropin (ACTH) and corticosterone. This study investigated whether the ACTH and corticosterone responses to tumor necrosis factor (TNF)-alpha and IL-6, two principal proinflammatory cytokines, are also modulated by the sex steroid milieu in the rat. Mature male and female rats received an intravenous administration of TNF-alpha(10 microg/kg) and IL-6 (10 microg/kg), and changes in plasma ACTH and corticosterone levels were determined over time. The effect of gonadectomy on the hormonal responses was also examined in both sexes. TNF-alpha induced significantly higher responses of ACTH and corticosterone in females than in males, and this sexual difference was abolished by gonadectomy in both sexes. By contrast, the hormonal responses to IL-6 were not significantly affected by either gender or gonadectomy. These results suggest a sex steroid-dependent modulation of the TNF-alpha-induced, but not the IL-6-induced, ACTH and corticosterone secretion in the rat. Further evidence for the sexually dimorphic neuroimmunoendocrine activity is reported herein.