Strain-dependent response to stimulation in middle-aged rat macrophages: A quest after a useful indicator of healthy aging

Lactobacillus rhamnosus Affects Rat Peritoneal Cavity Cell Response to Stimulation with Gut Microbiota: Focus on the Host Innate Immunity

Gut microbiota contribute to shaping the immune repertoire of the host, whereas probiotics may exert beneficial effects by modulating immune responses. Having in mind the differences in both the composition of gut microbiota and the immune response between rats of Albino Oxford (AO) and Dark Agouti (DA) rat strains, we investigated if intraperitoneal (i.p.) injection of live Lactobacillus rhamnosus (LB) may influence peritoneal cavity cell response to in vitro treatments with selected microbiota in the rat strain-dependent manner. Peritoneal cavity cells from AO and DA rats were lavaged two (d2) and seven days (d7) following i.p. injection with LB and tested for NO, urea, and H₂O₂ release basally, or upon in vitro stimulation with autologous E.coli and Enterococcus spp. Whereas the single i.p. injection of LB nearly depleted resident macrophages and increased the proportion of small inflammatory macrophages and monocytes on d2 in both rat strains, greater proportion of MHCII^hiCD163^- and CCR7⁺ cells and increased NO/diminished H₂O₂ release in DA compared with AO rats suggest a more intense inflammatory priming by LB in this rat strain. Even though E.coli- and/or Enterococcus spp.-induced rise in H₂O₂ release in vitro was abrogated by LB in cells from both rat strains, LB prevented microbiota-induced increase in NO/urea ratio only in cells from AO and augmented it in cells from DA rats. Thus, the immunomodulatory properties may not be constant for particular probiotic bacteria, but shaped by innate immunity of the host.

The involvement of estrogen receptors α and β in the in vitro effects of 17β-estradiol on secretory profile of peritoneal macrophages from naturally menopausal female and middle-aged male rats

The systemic and extra- gonadal levels of 17β-estradiol (E2) change during aging, and affect the expression of estrogen receptors (ERs) in the immune cells of both females and males. The age-related cessation of ovarian function in females, as well as the tissue-specific expression of enzyme aromatase (estrogen synthase which significantly rises with the advancing age) in both males and females, both determine the concentration of E2 to which immune cells may be exposed. The present study was set up to investigate the direct influence of E2 in vitro on the secretory profile of peritoneal macrophages from young and naturally menopausal female rats, and from young and middle-aged male rats. The involvement of receptor(s) responsible for mediating the effects of E2 in vitro was examined by use of antagonists specific for ERα or ERβ. Whereas in macrophages from young female rats E2 treatment diminished interleukin (IL)-1β secretion, it increased it in young males, and the middle-aged females. The in vitro E2 treatment increased tumor necrosis factor (TNF)-α release by macrophages from young rats of both sexes, while it increased macrophage IL-6 release independently of both sex and age. At the same time, E2 decreased hydrogen peroxide (H₂O₂) production in macrophages from females, and increased it in male rats of both ages, whereas it diminished nitric oxide (NO) release in all experimental groups. Inspite of the sex- and age-specific effects of E2 on macrophage urea release, E2 did not affect the NO/urea ratio in macrophages from female rats, and diminished it in macrophages from both young and middle-aged male rats. Independently of the sex and age, E2 stimulated the release of inflammatory cytokines predominantly via macrophage ERα, and inhibited the IL-1β release in young females via ERβ. In contrast, E2 increased macrophage H₂O₂ and urea production by activating ERβ, but diminished their release via ERα. Our study may contribute to better understanding of the complex role(s) that E2 may play in innate immunity during aging, and that are dependent of sex.

Sex Differences in Macrophage Functions in Middle-Aged Rats: Relevance of Estradiol Level and Macrophage Estrogen Receptor Expression

The aim of this study was to examine the influence of sex on age-related changes in phenotype and functional capacity of rat macrophages. The potential role of estradiol as a contributing factor to a sex difference in macrophage function with age was also examined. Thioglycollate-elicited peritoneal macrophages derived from the young (2 months old) and the naturally senescent intact middle-aged (16 months old) male and female rats were tested for cytokine secretion and antimicrobial activity (NO and H₂O₂ production and myeloperoxidase activity). Serum concentration of estradiol and the expression of estrogen receptor (ER)α and ERβ on freshly isolated peritoneal macrophages were also examined. Decreased secretion of IL-1β and IL-6 by macrophages from middle-aged compared to the young females was accompanied with the lesser density of macrophage ERα expression and the lower systemic level of estradiol, whereas the opposite was true for middle-aged male rats. Macrophages in the middle-aged females, even with the diminished circulating estradiol levels, produce increased amount of IL-6, and comparable amounts of IL-1β, TNF-α, and NO to that measured in macrophages from the middle-aged males. Age-related changes in macrophage phenotype and the antimicrobial activity were independent of macrophage ERα/ERβ expression and estradiol level in both male and female rats. Although our study suggests that the sex difference in the level of circulating estradiol may to some extent contribute to sex difference in macrophage function of middle-aged rats, it also points to more complex hormonal regulation of peritoneal macrophage activity in females.