Intrauterine transfusion for rhesus alloimmunization elevates fetal beta2-microglobulin levels

Intrauterine transfusions for rhesus alloimmunization leads to alterations in circulating T-cell populations. Given that elevations in circulating beta2-microglobulin are a marker of T-cell-mediated organ transplant rejection, we evaluated the effect of intrauterine transfusion on fetal beta2-microglobulin levels.Umbilical venous samples were obtained immediately prior to initial transfusion in ten anemic fetuses and in 12 fetuses with prior transfusions. Samples were also obtained from 18 gestational age-matched non-anemic fetuses and eight healthy neonates.The median concentration of beta2-microglobulin was significantly higher in fetuses with prior transfusions compared with non-anemic controls. In non-anemic controls, and in transfused fetuses, beta2-microglobulin levels decreased throughout gestation (r = -0.69, p = 0.01; and r = -0.80, p = 0.01, respectively). Among anemic and transfused fetuses, beta2-microglobulin levels displayed a negative correlation with fetal hematocrit (r = -0.62, p0.05; and r = -0.58, p = 0.04, respectively).We conclude that intrauterine transfusion for fetal anemia is associated with increased beta2-microglobulin levels, suggesting immunomodulatory effects of intrauterine transfusion on host immune responses to donor leukocyte antigens.