Muscle Injury and Aging Differentially Shape Immune Responses to Influenza Vaccination

The muscle environment during intramuscular vaccination has the potential to shape downstream immune responses, yet this relationship remains poorly defined. We hypothesize that muscle condition at the time of vaccination matters for the outcome of vaccination. In this study, we examined how glycerol-induced muscle injury at the time of quadrivalent inactivated influenza vaccine (QIV) administration can skew host immune responses to vaccination and modulate systemic and mucosal immunity following subsequent H1N1 challenge three weeks later. Given that seasonal influenza disproportionately affects older adults, and that muscle regenerative capacity is both sex- and age-dependent, we addressed sex and age as biological variables. We found that muscle injury during QIV vaccination promoted regulatory T cell and M2 macrophage levels in the lungs upon subsequent H1N1 infection three weeks later, with responses more pronounced in young females and diminished with age in both sexes. Muscle injury also shifted antibody isotype distribution away from IgG2c toward IgG1 in young male and aged mice, without altering total hemagglutinin-specific antibody titers. In young influenza virus-infected mice, prior QIV vaccination resulted in a type 2–skewed mucosal immune response, marked by IL-4, IL-5, IL-13, and eosinophilia, whereas this response was attenuated in aged cohorts. Finally, because IL-33 is a pro-regenerative alarmin reduced in aging muscle, we tested the impact of IL-33 supplementation. IL-33 enhanced vaccine-specific antibody production across age groups and restored type 2 mucosal immunity in aged mice, thereby partially rescuing the age-associated impairment of the host response to infection, although it did not enhance glycerol damage-dependent regulatory T-cell influx into the lungs after infection as observed in young mice. Our data show that muscle health at the time of vaccination can impact host vaccine responses that shape the lung immune environment during subsequent respiratory infection and highlight IL-33 as a target for vaccine adjuvants.