The function of PSG9 (pregnancy specific beta-1-glycoprotein 9, ENSG00000183668) is as follows. Binds to the small latent transforming growth factor-beta complex, consisting of the N-terminal TGFB1 latency-associated peptide (LAP) and the mature form of TGFB1, thereby leading to the activation of TGFB1 (PubMed:27389696). The activation of TGFB1 leads to stimulation of naive CD4(+) T-cells to increase FoxP3 expression and to an increase in the number of FoxP3(+) regulatory T-cells (PubMed:27389696). Induces the differentiation of a suppressive CD4(+)LAP(+)FoxP3(-) T-cell subset (PubMed:27389696). Induces the secretion of TGFB1 in macrophages, but not in activated CD4(+) T-cells (PubMed:27389696). May reduce the expression of several pro- inflammatory cytokines and chemokines by CD4(+) T-cells, including IL2 and IL6 (PubMed:27389696). .