Lymphocyte suppressor and stimulatory factors within uterine luminal protein secretions of pregnant gilts

Immunosuppressive macromolecules of endometrial and conceptus origins in livestock species

Since the mid- to late-1970s, intrauterine immunosuppressive macromolecules recovered from endometrial and conceptus secretions have been reported for livestock species. Using primarily in vitro assays, in conjunction with a limited number of techniques conducted in vivo, these macromolecules were shown to suppress various T-cell responses. Some macromolecules were also shown to suppress cytolytic activities of non T-cells. It remains unknown as to whether these macromolecules actually afford protection to the conceptus by suppressing cell-mediated immune responses directed toward conceptus tissues. Endometrial effector cells in the ewe respond to antigenic stimulation and preattachment trophoblastic cells of pigs and sheep can be lysed by effector cells. Consequently, these observations suggest a need for immunosuppression, either locally at placentation sites or within the entire uterus. This review describes the intrauterine macromolecules that have been shown to suppress lymphocyte responses. Additional information, although limited at this time, refers to their origin and possible mechanisms of action. As more reagents become available to complete the identification of the intrauterine immune cells in livestock animals, experiments (e.g. antibody-mediated depletion of cells) can be conducted to determine the precise functions of all these cells. Knowing their functions will help delineate whether or not immunosuppressive macromolecules have a role in the regulation and maintenance of conceptus tissues during pregnancy.

Immunosuppressive activity of a porcine high-molecular weight uterine macromolecule is associated with transforming growth factor-beta

A > or = 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-beta (TGF-beta) was added to additional cultures in order to determine whether suppressor activity of high-molecular weight macromolecules was associated with TGF-beta. The > or = 230 kDa component suppressed (P < 0.0005) TdR incorporation into PHA-treated PBL and anti-TGF-beta 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 (> or = 4 x 10(6) Da (> or = 4 MDa), eluted at the void volume) which suppressed (P < 0.05) TdR incorporation into PHA-treated PBL. Anti-TGF-beta 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 > or = 4 MDa macromolecule which suppresses proliferative responses of PBL and likely serves as a carrier for TGF-beta.

Temporal patterns of secretion of porcine uterine suppressor and stimulatory macromolecules

Temporal secretory patterns of porcine uterine suppressor (>/=230 kD) and stimulatory (29 kD) macromolecules were evaluated within uterine luminal protein (ULP) secretions recovered during early pregnancy. The ULP was recovered by uterine flushing from four Landrace gilts each on Days 9, 12, 15 and 18 of pregnancy. Unfractionated and fractionated ULP (using Sephacryl S-200) was tested for suppression or stimulation of phytohemagglutinin-induced peripheral blood T-lymphocyte proliferation. For all days of pregnancy, unfractionated ULP suppressed (P<0.002 to 0.0001) lymphocyte proliferative responses, with the greatest (P<0.05) activity observed for ULP collected on Day 9 of pregnancy. Suppressor activity resulted from the >/=230 kD component, in which the activity was greater (P<0.05) for ULP from gilts on Day 9 than Days 12, 15 and 18 of pregnancy. The 29 kD component failed (P>0.05) to stimulate lymphocyte proliferation, although there was a nonsignificant stimulatory trend for 2 of 4 gilts each at Days 12 and 15 of pregnancy. These findings demonstrate a temporal secretory pattern for the >/=230 kD lymphocyte suppressor component, which may be requisite for the immunological survival of the conceptus during early pregnancy. The inconsistent appearance of the lymphocyte stimulatory factor (29 kD component) tends to minimize its biological significance relative to the immunology of pregnancy.

Immunostimulatory factor(s) in the porcine uterine fluids

The effects of porcine uterine fluid filtrate (PUF) on lymphocyte activity were examined. PUF was added to porcine lymphocyte cultures in the presence or absence of phytohemagglutinin (PHA), concanavalin A (Con A), or pokeweed mitogen (PWM). Lymphocyte response was determined by 3H-thymidine incorporation. Results indicated that PUF enhanced PHA-, Con A-, and PWM-induced lymphocyte mitogenesis by 222%, 207%, and 261%, respectively, as compared to control. The stimulatory effect of PUF was unlikely to be due to the presence of interleukin-2 in PUF, by evidence that PUF alone did not support cytotoxic T-lymphocyte proliferation, nor was the stimulatory effect due to microbial contamination, because treatment of PUF through PyroBind columns to remove endotoxin did not affect its activity. Incubation of PUF at 56C for 40 min did not alter the enhancement effect. Treatment of PUF with trypsin or pronase for up to 24 hr did not change its activity. In mixed lymphocytes reaction, PUF augmented 3H-thymidine uptake by 242%. The molecular (mol) mass of the immunostimulatory activity in PUF was examined by size-exclusion HPLC, Sephadex G-50, and G-15 gel filtration, and it was found to be 0.8 kDa and < 0.5 kDa. Extracts of porcine endometrium also enhanced PHA-induced lymphocyte mitogenesis, suggesting that the factor(s) may be of uterine origin. In conclusion, we have identified an factor(s) in PUF capable of stimulating lymphocyte mitogenesis and mixed lymphocyte reaction.