Estradiol enhances influenza vaccine responses through B cell metabolic reprogramming in female mice

Reproductive-aged females mount stronger antibody responses to influenza vaccination than males, with the sex difference waning in older age. Estradiol has been implicated as a driver, but the mechanisms mediating how estradiol affects B cell function remain elusive. Adult (3 months) and aged (17 months) male and female mice were vaccinated and boosted with inactivated influenza vaccine. Metabolomics analysis of splenic B cells revealed that adult female B cells were enriched in lipid metabolic pathways, whereas B cells from males were enriched in central carbon-associated pathways following vaccination. B cells from vaccinated adult females exhibited greater expression of mTOR and related proteins than those from males, a difference diminished in aged mice. In adult females, estradiol depletion reduced, and replacement increased, mTOR activity in B cells, particularly in germinal center B cells and plasmablasts in lymphoid tissues, and plasma cells in bone marrow. In males, neither testosterone depletion nor repletion altered B cell metabolism. These findings are consistent with evidence that estradiol enhances mTOR activation via estrogen receptor α (ERα) signaling, suggesting coordinated regulation between estrogen and mTOR signaling in B cells. Inhibition of mTOR with rapamycin impaired vaccine-induced antibody responses and protection in adult females. In aged females, supplementation with estradiol or treatment with a selective ERα agonist increased mTOR signaling and enhanced antibody responses compared with mock-treated aged females. These data identify estrogen signaling as a regulator of B cell metabolism that supports greater expansion and function of antibody-secreting cells following vaccination in females compared with males. IMPORTANCE: Vaccine-induced immunity differs between the sexes, with adult females mounting stronger antibody responses to influenza vaccination than age-matched males. We show that estradiol in females regulates B cell metabolism to promote the maturation and metabolic activation of antibody-secreting B cells, thereby enhancing humoral immunity and protection following vaccination. mTOR signaling in B cells was greater in adult females than males after vaccination, which was diminished with aging or depletion of estradiol. Therapeutic treatment of aged females with either estradiol or a selective estrogen receptor α modulator increased mTOR signaling and improved vaccine-induced antibody responses, thereby eliminating the effects of aging on influenza immunity. Harnessing estrogen-signaling mechanisms to improve responses to influenza vaccines could be a novel therapeutic strategy to improve public health.