Expression of CD4⁺/CD25⁺ T_reg (T-regulatory) cells is increased during normal pregnancy

Abstract

Blood from healthy non-pregnant, pregnant and postnatal women was used. Circulating lymphocytes were phenotyped using the whole blood FACS lysis method. Multicolour analysis was used to identify CD4⁺/CD25⁺ cells with low forward light scatter, thereby differentiating T_reg cells from activated lymphocytes. Functional studies confirmed these cells to have suppresser activity. The median proportion of T_reg cells was 4.4% (range 2.3–8.0) in the non-pregnant women vs. 9.2% (3.4–28.1) in pregnancy (P < 0.0001). Evidence that these small CD4⁺/CD25⁺ T cells were T_reg cells rather than recently activated T cells included negative vs. for activation markers DR (88–94%) and CD69 (94–98%), and no increased expression of CD11a or CD18. CD45RO was present on 34–52%, indicating either previous exposure to antigen or that some of these cells may have reverted to CD45RA expression. CXCR3, previously reported on T_reg cells and an important chemokine receptor for migration into allografts, was found on 38–50% of T_reg cells in pregnancy.