Regulation of mitogen- and TCGF-induced lymphocyte blastogenesis by prostaglandins and supernatant from equine embryos and endometrium.

This research explores the immunosuppressive substances in early pregnancy, focusing on how these substances, released by embryos and endometrium, interfere with lymphocyte blastogenesis. The study establishes that these substances, notably certain types of prostaglandins and fluid from equine embryos and endometrium, have a direct inhibitory effect on T cell growth and lymphocyte blastogenesis – a process vital to immune system function.

The Experiment

• The research began with in vitro culturing of embryos and endometrium tissues from mares in early pregnancy. In this context, in vitro means outside the living organism, in a controlled lab environment.
• In order to determine the role of prostaglandins (lipid compounds that have diverse hormone-like effects) in the immunosuppression process, the team used a prostaglandin-synthesis inhibitor known as indomethacin. This substance effectively suppresses the production of prostaglandins.
• A series of prostaglandins were added to equine lymphocytes (white blood cells vital in the immune system response). Lymphocyte proliferation (increase in cell numbers) was then observed after the addition of substances known as concanavalin A (Con A) or phytohaemagglutinin A (PHA), which are known to stimulate cell division.

Findings

• Two specific types of prostaglandins, PGE2 and PGF2 alpha, were found to significantly inhibit Con A-induced blastogenesis (the process of generating precursor immune cells).
• Other prostaglandins tested, 6-keto-PGF1 alpha and 13,14-dihydro-15-keto-PGF2 alpha, did not affect this response.
• The researchers also investigated the effect of the prostaglandins on PHA-induced blastogenesis, and found that PGE2, PGF2 alpha, and 6-keto-PGF1 alpha all had an inhibitory effect. However, at all tested concentrations, 13,14-dihydro-15-keto-PGF2 alpha only slightly reduced the blastogenesis process.
• PGE2 was identified as the sole prostaglandin, tested at physiological concentrations, that significantly inhibited the incorporation of [3H] thymidine, a radioactive substance used in cell proliferation assays. Consequently, PGE2 was the main focus in subsequent investigations.

Further Investigation on PGE2

• Initially, the researchers added PGE2 and T cell growth factors (TCGF, substances that promote the growth of T cells, a type of white blood cell responsible for immune responses) to TCGF-responsive lymphocytes. They observed PGE2 reduced the TCGF-mediated blastogenesis in a dose-dependent manner, meaning the inhibitory effect increased with higher doses.
• Culture supernatant (the liquid surrounding cultured cells) from embryos and endometrium from 14-day pregnant mares also inhibited the TCGF-induced lymphocyte blastogenesis.

Conclusions

• The research concluded that PGE2 interferes with lymphocyte blastogenesis in TCGF-dependent mechanisms.
• It suggests that PGE2, found in the uterus of the early pregnant mare, could be one of the factors instrumental in immunosuppression at the time of maternal recognition of pregnancy.