Marilen Benner

CHAPTER 2 30 Decidual T cells are more experienced than endometrial T cells We next examined endometrial and decidual T cell subsets in more detail to know if the observed phenotype of more differentiated memory T cells in decidua compared to PBMC (35) would also apply to endometrium. Compared to MMC derived T cells, DPMC derived T cells revealed a significantly lower percentage of CD45RA + (53.4%±8.8% and 17.2%±7.4%, respectively) and a higher percentage of CD45RO + cells (28.9%±8.0% and 66.4%±11.7% respectively) (Figure 2b). In addition, we subdivided CD4 + and CD8 + T cells into naive T cells (CD45RA + CCR7 + ), effector T cells (Teff, CD45RA + CCR7 - ), effector memory T cells (EM, CD45RA - CCR7 - ), and central memory T cells (CM, CD45RA - CCR7 + ). Both CD4 + and CD8 + T cells present in DPMC were significantly less naive compared to MMC, while a significantly higher percentage of EM and CM T cells was present in DPMC (Figure 2c). Thus, over the course of pregnancy, decidual T cells appear to acquire an experienced and differentiated phenotype. To strengthen the claim that endometrial T cells are primed over the course of pregnancy and can differentiate towards a phenotype found in the decidua, we performed in vitro experiments whereby endometrial lymphocytes were stimulated with either rhIL-15 or anti-CD3/anti-CD28 mAb microbeads alone, or in combination. The rationale for using IL-15 is because IL-2 is hardly detected in decidua and after implantation, endometrial NK cells start to differentiate as a result of local IL-15 production (9). After 5 days of culture, the distribution of T cell subsets was measured with flow cytometry in the same way as above. Endometrial T cells stimulated with anti-CD3/anti-CD28 mAb microbeads reveal a similar subset division as found in term decidual T cells, i.e. less naive T cells and more EM and CM T cells compared to control (medium) and day 0 (Supplementary Figure S3). Whereas stimulation with IL-15 alone was not sufficient to lead to a similar differentiation, IL-15 did appear to have an effect on T cell differentiation when administered together with anti-CD3/anti-CD28 beads and as compared to the bead alone condition, i.e. more EM and less CM T cells. This may suggest that T cells need an additional TCR trigger before they can differentiate towards a more mature phenotype. These in vitro data showed that endometrial lymphocytes can be differentiated towards a phenotype reminiscent of term decidual T cells, which lends further support for the notion that over the course of pregnancy decidual T cells appear to acquire an experienced and differentiated phenotype.