Reseach assistant UW Madison MADISON, Wisconsin, United States
Disclosure(s):
Mona Mohamed, MD, MSc: No financial relationships to disclose
Introduction/Rationale: Decidual natural killer (NK) and T cells undergo compositional changes during pregnancy, yet the mechanisms regulating their origin and maintenance remain unclear.Using T-bet fate mapping mice(B6.RosaRFP;Tbx21-Cre) with serial intravascular labeling (SIVL) and BrdU incorporation, we tracked how trafficking and local proliferation coordinate lymphocyte homeostasis across gestation
Methods: Non-pregnant and pregnant mice at GD7-8 and GD12-14, received BrdU intraperitoneally and sequential αCD45 tail-vein injections (AF488 at 24 hours and AF647 at 5 minutes) before sacrifice. Decidual Leukocytes were isolated, stained with αCD45 (APC/Fire810) and lineage markers for B, T, NK, and classified as continuously circulating (CC), recent emigrant (RE), recent immigrant (RI) or unlabeled cells as tissue localized (TL)
Results: SIVL showed that at GD7-8, TL fraction of CD4+, CD8+ and NKs declined (P=0.001, P=0.0007, P=0.001) with increased CC CD4+andCD8+ T cells (P=0.01,0.02), and RI NKs (P=0.0001), versus virgin. TL reduction was smaller for NK than CD4+ and CD8+ T cells (P=0.008, 0.001). TL NKs showed elevated proliferation(P=0.004, vs virgin) limited to decidua and absent in splenic NKs or decidual T cells, suggesting local expansion may sustain early TL NK pool. By GD12-14, NK proliferation sharply decreased, coinciding with further reduction of TL NK fraction (P < 0.0001,P=.004 vs GD7-8), while CD4+ and CD8+ T cells began proliferating(P=0.006, 0.01,vs virgin), with stronger CD4+ expansion (P=0.03) and a higher CD4⁺/CD8⁺ ratio(P < 0.0001,vs virgin). Interestingly, proliferation at this stage involved T-bet independent NK and CD8+ cells, suggesting a shift to less cytotoxic profile. However, CC, RI, TL and RE fractions within CD4+andCD8+T cells remain comparable.
Conclusion: Our findings reveal a gestational stage-specific coordination of trafficking and proliferation that maintains decidual immune homeostasis, marked by early NK proliferation and mid-gestation T cell expansion reflecting on CD4+/CD8+ ratio.
