A ≥ 230 kDa lymphocyte suppressor component recovered from uterine luminal protein (ULP) secretions of Landrace and Yorkshire gilts on day 15 of pregnancy was further purified by anion-exchange (DEAE Sepharose CL-6B) and gel filtration (Sepharose CL-6B) chromatography. Macromolecules within each peak fraction were tested for suppression of thymidine (TdR) incorporation into phytohemagglutinin (PHA)-treated peripheral blood lymphocytes (PBL). A neutralizing antibody to transforming growth factor-β (TGF-β) was added to additional cultures in order to determine whether suppressor activity of high-molecular weight macromolecules was associated with TGF-β. The ≥ 230 kDa component suppressed (P < 0.0005) TdR incorporation into PHA-treated PBL and anti-TGF-β reversed (P < 0.034) the suppressor response. Following anion-exchange chromatography of this component, suppressor activity was greatest (P < 0.05) for an acidic component (fraction III), which comprised 45.9% of eluted macromolecules. Sepharose CL-6B chromatography of fraction III resulted in a major (58.7% of eluted macromolecules) component (≥ 4 10 6 Da (≥ 4 MDa), eluted at the void volume) which suppressed (P < 0.05) TdR incorporation into PHA-treated PBL. Anti-TGF-β reduced the suppressor activity of this macromolecule by 34.2%. Suppressor responses were not associated with viabilities of PBL. These data demonstrate that ULP secretions from gilts on day 15 of pregnancy contain a ≥ 4 MDa macromolecule which suppresses proliferative responses of PBL and likely serves as a carrier for TGF-β.
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