Effect of pregnancy on thymic T cell development.

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, post-partum 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 alpha, beta+ 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.