Which statement is true regarding physiologic immunology changes during pregnancy

• A. Fetus Develops Behind the Stratum Trophoblast and Trophoblast Cells Express HLA-A and HLA-B
• B. The Cellular Part of the Mother's Immune System Will Be Activated
• C. Pregnant Women Are Sensitive to Flu Infection Because of Suppressed Cell-Mediated Immunity
• D. Increased Activity of Mother's NK Cells Increases Fetal Immune Failure Risk

Answer: (C)

During pregnancy, the maternal immune system shifts to tolerate the fetus, dampening cell-mediated (Th1) immunity and favoring a humoral (Th2) response. This reduced cell-mediated immunity means control of intracellular pathogens, including viruses, can be less robust. Influenza relies heavily on cytotoxic T cells and other cell-mediated responses; when those are downregulated in pregnancy, women can be more susceptible to flu or experience more severe disease. This is why the statement linking increased flu vulnerability to suppressed cell-mediated immunity best reflects physiologic immunology changes during pregnancy.

Other points are less accurate: fetal trophoblasts express nonclassical HLA molecules like HLA-G (and HLA-C) to promote tolerance, not HLA-A and HLA-B. The maternal immune system’s cellular arm is not broadly activated during pregnancy; it is modulated toward tolerance. While decidual NK cells play a role in placentation, their activity is tightly regulated rather than simply increased in a way that raises fetal immune failure risk.