• Pregnancy;
  • suppression;
  • thymus

PROBLEM: The thymus gland decreases in size during pregnancy. The significance of this alteration is not known.

METHOD: In this report, we examined thymic function by evaluating the development of T lymphocytes in the thymus of pregnant Balb/c mice at 15 and 20 days gestation using multi-color flow cytometry. Comparative analysis was made with non-pregnant mice, postpartum lactating mice, and postpartum non-lactating mice.

RESULTS: Progressive reduction of thymic size and cellularity during pregnancy was observed. All of the CD4 and CD8 defined subsets were reduced, with a disproportionate loss of CD4+, CD8+ double positive cells. Examination of the CD4-, CD8- double negative compartment revealed a predominance of TCR α,β+ double negative cells, and a striking loss of precursor cells. The CD3-, CD4-, CD8- triple negative thymic subset was composed almost entirely of the earliest population (CD44+, CD25-), with the remaining maturational stages (CD44+, CD25+; CD44-, CD25+; and CD44-, CD25-) depleted. At 2 weeks postpartum, the subset ratios normalized, and the total cell count showed recovery.

CONCLUSION: T cell development is blocked at the precursor level during the mouse pregnancy. These effects are transient, and gradual recovery is observed in the postpartum period.