Biological sex, not reproductive cycle, influences peripheral blood immune cell prevalence in mice

Key points Traditionally the female sex, compared with male has been perceived as having greater variability in many physiological traits, including within immune system. We investigated effects of biological sex and reproductive cycle on numbers circulating leukocytes C57BL/6J mice. show that but not cyclicity, a significant effect peripheral blood cell prevalence variability, differences were consistent amongst common inbred laboratory mouse strains. found mice, have immunophenotype, this was influenced by body weight. created summary tables for researchers to facilitate experiment planning sample size calculations cells consider sex. Immunophenotyping (i.e. quantifying number types leukocytes) is used characterize changes during health disease, response pharmacological other interventions. Despite importance function, there considerable uncertainty extent which or influence immunophenotype. quantified multicolour flow cytometry young mice assessed cycle, experimental factors data variability. are no B cells, NK CD4+ T CD8+ monocytes, neutrophils. Immunophenotype composition do significantly change between stages cycle. There are, however, sex-specific prevalence, fewer neutrophils, Surprisingly, immunophenotype more variable weight contributing factor. provide tools perform priori two-group factorial analyses. varies strains, using equal sizes always appropriate within-sex evaluations populations blood.