Decreased suppressors of
cytokine signaling (SOCS) activity in human gestational tissues may play a part in the onset/progression of term labor. Since
SOCS proteins negatively regulate
cytokine-mediated inflammatory processes, we hypothesized that
SOCS proteins are elevated in gestational tissues from spontaneous preterm deliveries with intrauterine
infection. SOCS1, -2 and -3 mRNAs and
proteins were detectable by RT-PCR and immunoblotting respectively, in preterm amnion, choriodecidua and placenta, irrespective of
infection status. Immunoperoxidase staining localized SOCS1, -2 and -3 to all cell types of the gestational membranes, with infiltrating leukocytes reacting strongly in infected tissues. In villous placenta, SOCS was immunolocalized to the syncytiotrophoblast with marked staining of round mesenchymal cells, possibly Hofbauer cells. Nuclear SOCS staining was seen in amnion, chorion and placental syncytiotrophoblasts.
SOCS proteins were, in general, significantly more abundant in placenta compared with amnion or choriodecidua. Placental SOCS1 and
interleukin-1beta concentrations were positively correlated (r(2)=0.47; P<0.05). However, no changes in SOCS levels in any tissues were observed with intrauterine
infection. The relatively large amounts of
SOCS proteins in the placenta may reflect a placenta-specific immunoprotective response to minimize the elaboration and effects of
cytokines with potential to harm the placenta and fetus. Lack of labor-associated changes in SOCS levels suggests that the regulation of SOCS expression in preterm gestational tissues differs from those at term, perhaps reflecting roles in regulating placental somatotropic responses.