Cells Changes Functions References
T lymphocytes Decreased/unaffected from follicular to luteal phase Defensive or destructive for the developing embryo depending on particular subset of cells [29, 30, 31, 32]
T helper cells (Th1, Th2, Th17)
Lower levels during mid-luteal and late luteal phase as compared to early follicular phase.
Th1 cells manufacture pro-inflammatory cytokines Th2 cells cytokines with anti-inflammatory effects Th17 cells also produce pro-inflammatory type of cytokines
[33]
B lymphocytes Slightly increased toward the end of luteal phase Still uncertain, possibly involved in early stage of pregnancy [34, 35, 31]
Uterine dendritic cells (uDCs) Controversially immature DCs show an increasing trend from follicular to luteal phase and reach to peak level during menstrual phase. However, mature DCs remain unchanged during reproductive cycle Implicated embryo acceptance, remodeling of uterus, angiogenesis, invasion and differentiation of trophoblasts, decide the differentiation of progenitors of T cells into Tregs as well as the activation and proliferation of Tregs [30, 36, 37-42]
Uterine natural killer (uNK) cells Show gradual rise from follicular to luteal phase and reaches maximum level in end of luteal phase and decidua of pregnancy Remodeling of spiral arteries, regulation of invasion of trophoblasts, angiogenesis enhancement [9, 29, 30, 34, 43-46]
Treg cells Proliferate in pre-implantation endometrium, increased at decidual site for implantation and during early period of pregnancy until mid-gestation Treg cells are crucial for regulating extreme maternal inflammatory reaction at the site of implantation, participate in materno-immune tolerance to embryonic allograft mainly during early stage of pregnancy, blocking maternal effector T cells implicated in regulating the remodeling of maternal vasculature [32, 34, 36, 47-53]
Lymphocytes Significantly declined from follicular to luteal phase Potentially toxic for embryo and as a result blocked during successful gestation [31, 32, 35, 54]
Neutrophil granulocytes Show remarkable elevation during late luteal phase Involved in menstruation, breaking down and repairing of tissue. Exert pro-angiogenic and tolerogenic effects in the decidua of pregnant women [35, 55-57]
Macrophages Increase gradually from follicular phase to luteal phase and attain peak density prior to menses and during pregnancy Participate in the maintenance of corpus luteum, implantation of blastocyst, spiral artery remodeling, regulation of invasion of trophoblasts, embryonic protection against intra-uterine infection [27, 30, 34, 36, 58-61]
Mast cells Remain unaltered except phenotypical changes during menstrual cycle and become activated during early and mid-luteal phase Involved in the commencement of menses, enhancing the remodeling of tissue and spiral arteries, supporting the process of implantation as well as angiogenesis [34, 62, 63]