SEX-DIFFERENCES IN HOST-RESISTANCE TO MYCOBACTERIUM-MARINUM INFECTION IN MICE

Sex differences were observed in host resistance to Mycobacterium marinum infection in mice. Males were found to be more susceptible than females in terms of mortality, incidence of gross skin lesions, and bacterial load in the lungs and spleen. The degree of sex differences varied from strain to strain of test mice, in the order C3H/He, A/J, and BALB/c > DBA/2, B10.A, and C57BL/6, on the basis of survival time and multiplication of organisms in the visceral organs. Although this ordering corresponded to the susceptibilities of both male and female mice to the organisms, much greater strain dependency was seen in males than in females. Castration caused an increase in the host resistance of males, but this effect was substantially reversed by continuous testosterone treatment. Testosterone also increased the susceptibility of female mice to this infection. These findings imply that the male sex hormone is involved in the lowered anti-M. marinum resistance of males. Although athymic mice were more susceptible than euthymic mice, a substantial degree of sex difference was also observed in the T-cell-depleted animals, indicating that natural host resistance to this infection is sex dependent. Indeed, more efficient macrophage mobilization at the site of infection was seen in females than in males. Although female T-cell transplantation improved the lowered resistance of athymic mice, there was a sex difference in bacterial growth in the lungs. This implies that sex hormones affect T-cell functions.