The numbers of T and B lymphocytes increase in the decidua throughout gestation. In contrast, decidual macrophage numbers remain relatively invariant throughout normal gestation.
The mechanisms for controlling leukocyte trafficking in the placental bed are poorly understood.
However, previous studies have shown that multiple chemotactic and chemostatic factors are produced at the fetal-maternal interface, supporting the concept that an elaborate chemokine network controls leukocyte recruitment and maintenance throughout normal and pathological pregnancies.
Colony stimulating factor 1 (CSF1; also known as macrophage-colony stimulating factor or M-CSF) is a 45-90-kDa homodimeric glycoprotein that regulates the proliferation and differentiation of the mononuclear phagocytic cell lineage. CSF1 acts via a high affinity cell surface receptor product of the CSF1R proto-oncogene to affect macrophage viability, differentiation, chemoattraction, motility, and adhesion. Furthermore, CSF1 helps to maintain pregnancy by mediating trophoblast-endometrial interactions. Confirmation of the crucial role played by CSF1 in pregnancy has come from studies of osteopetrotic (op/op) mice, which carry an inactivating mutation in the coding region of CSF1.