Major Histocompatibility Complex I Mediates Immunological Tolerance of the Trophoblast during Pregnancy and May Mediate Rejection during Parturition

Table 2

Leukocytes that have been found in the placenta during physiological pregnancy in humans, cows, and horses [29–33].

	Humans	Cows	Horses
Leukocytes in placenta	Three major populations: (i) Uterine Natural Killer (uNK) cells; (ii) Macrophages; (iii) T lymphocytes; Other less abundant leukocyte populations: (i) Dendritic cells; (ii) Natural Killer T (NKT); (iii) Regulatory T cells	Endometrial macrophages (as much as half of all immune cells); Other less abundant; leukocyte populations: (i) Dendritic cells; (ii) T lymphocytes	Mostly T lymphocytes; Other less abundant; leukocyte populations: (i) B lymphocytes; (ii) NK cells; (iii) Eosinophils