Variables affecting toxicity of human sera in mouse embryo cultures

It has been reported that sera from women with reproductive disorders can inhibit mouse embryo development. While performing tests on this subject in our laboratory, two unexpected variables were identified that can influence the effect of human serum on mouse embryo cultures. In a standard embryo culture system in which heat-inactivated sera (10% final concentration) were added to two-cell mouse embryos and percentage blastocyst development was scored after 4 days, sera that had been collected into standard clinical Monoject blood collection red-stopper tubes were significantly more embryotoxic than sera collected from the same subjects into 15-ml Falcon centrifuge tubes (P less than 0.005). Furthermore, we observed that sera from laboratory personnel that worked with mice often inhibited mouse embryo development. To study this effect further, sera were collected from five fertile individuals who were routinely exposed to mice and from fertile women with no previous exposure to rodents. Sera from the mouse-exposed group were significantly more inhibitory than sera from the nonexposed control group (P less than 0.005). The effect was observed in the ammonium sulfate-precipitated immunoglobulin fraction of the mouse-exposed group's sera, and high titers of antibodies reactive with mouse spleen cells were detected in sera and immunoglobulin fractions from this group by enzyme-linked immunosorbent assay (ELISA). Embryotoxic activity was neutralized by absorption with mouse lymphocytes, but not with rabbit or human lymphocytes, suggesting that a heterophilic antimouse antibody is the factor responsible for this effect. These data emphasize the importance of including extensive controls in experiments addressing toxic effects of human sera on mouse embryos.