Sex steroid hormones enhance immune function in male and female Siberian hamsters

Immune function is better in females than in males of many vertebrate speci es, and this dimorphism has been attributed to the presence of immunosuppre ssive androgens in males. We investigated the influence of sex steroid horm ones on immune function in male and female Siberian hamsters. Previous stud ies indicated that immune function was impaired in male and female hamsters housed under short-day photoperiods when androgen and estrogen concentrati ons were virtually undetectable. In experiment 1, animals were gonadally in tact, gonadectomized (gx), or gx with hormone replacement. Females exhibite d the expected increase in antibody production over males, independent of h ormone treatment condition, whereas male and female gx animals exhibited de creased lymphocyte proliferation to the T cell mitogen, phytohemagglutinin (PHA) compared with intact animals, and this effect was reversed in gx hams ters following testosterone and estradiol treatment, respectively. In exper iment 2, testosterone, dihydrotestosterone, and estradiol all enhanced cell -mediated immunity in vitro, suggesting that sex steroid hormones may be en hancing immune function through direct actions on immune cells. In experime nt 3, an acute mitogen challenge of lipopolysaccharide significantly suppre ssed lymphocyte proliferation to PHA in intact males but not females, sugge sting that males may be less reactive to a subsequent mitogenic challenge t han females. Contrary to evidence in many species such as rats, mice, and h umans, these data suggest that sex steroid hormones enhance immunity in bot h male and female Siberian hamsters.