Sex and species differences in cell-mediated immune responses in voles

Males generally display reduced immune responses and greater susceptibility to disease than females, possibly reflecting the suppressive effects of androgens on the immune system. It is presumed that this androgenic effect on immune function is more pronounced among polygynous than monogamous species because concentrations of circulating androgens are generally higher among polygynous than monogamous males. The present study examined sex and species differences in cell-mediated immunity of two Microtus species. Cell-mediated immunity was assessed among individually housed polygynous meadow voles (M. pennsylvanicus) and monogamous prairie voles (M. ochrogaster) by examining the proliferative responses of splenocytes to the T-cell mitogen concanavalin A (Con A) and the B-cell mitogen lipopolysaccharide (LPS). Neither sex nor species differences were observed in response to stimulation with Con A. In contrast, meadow voles exhibited higher proliferative responses to LPS than prairie voles. Sex differences in immune function were only observed among prairie voles; males exhibited higher proliferative responses to LPS than females. Male meadow voles had higher circulating testosterone concentrations than male prairie voles and female prairie voles had higher estradiol concentrations than female meadow voles. Males of both Microtus species weighed more than conspecific females. The immunological differences were not related to differences in either body mass or hormone concentrations. Overall, these data do not support the hypothesis that higher androgen concentrations in polygynous males influence sex or species differences in immune function.