Maternal immune activation does not affect maternal microchimeric cells

We are naturally chimeras. Apart from our own cells originating from the fertilized egg, placental mammals receive small numbers of maternal cells called maternal microchimerism (MMc) that persist throughout one's whole life. Not only are varying frequencies of MMc cells reported in seemingly contradicting phenomena, including immune tolerance and possible contribution to autoimmune-like disease, but frequencies are observable even among healthy littermates showing varying MMc frequencies and cell type repertoire. These varying differences in MMc frequencies or cell types could be contributing to the diverse phenomena related to MMc. However, factors biasing these MMc differences remain largely unknown. Here, we tested whether immunological activation leads to differing MMc frequencies, based on our recent study that suggests that most maternal cells are immune-related. Unexpectedly, fluorescence-activated cell sorting analysis on the murine spleen, thymus, and liver following maternal immune activation by mid- gestational lipopolysaccharide intraperitoneal injections detected no significant difference in the number, or ratio of, immune-related maternal cells in the tested embryonic organs of healthy offspring. These findings suggest that MMc frequencies remain stable even under immune-activated conditions, implying a possible control system of MMc migration against changes in the immunological conditions.