Mortality, sex and microchimerism

Background We previously demonstrated that women with detectable male cells in peripheral blood – male origin microchimerism – enjoy half the risk of all-cause mortality compared with women tested negative. However, such differences are likely due to confounding. Also, we do not know whether better survival in women vs. men is confined to women who test male origin microchimerism positive. In this updated analysis, we first compared the survival of positive and negative women using prognostic score weighting to minimize potential confounding. Next, we compared the survival of women tested positive and negative for male origin microchimerism to men. Methods Women (n = 766) and men (n = 1,000) from the Diet, Cancer, and Health cohort aged 50–64 years in 1993–1997 were followed until 2017 for all-cause mortality in national Danish registers. Based on predictors of death, we calculated prognostic scores for all women, and compared mortality according to male origin microchimerism status by prognostic score weighted Cox regression adjusting for potential confounding. Next, we compared mortality across positive/negative women and men. Results Women who tested male origin microchimerism positive versus negative had a 53% lower mortality rate (adjusted HR = 0.47 [95% CI 0.32–0.69]). Compared with men, women who tested positive had a 41% lower mortality rate (HR = 0.59 [95% confidence interval (CI) 0.42–0.81]), whereas women who tested negative had a similar rate (HR = 0.83 [95% CI 0.63–1.10]). Conclusions Women who tested positive for male origin microchimerism lived longer than their counterparts who tested negative, who appeared to have a similar survival pattern to that of men.