Changes in nuclear factor kappa B components expression in the ovine spleen during early pregnancy

There is an immunological tolerance against foetal antigens, which is induced by hormonal changes during pregnancy (Fuhler, 2020). Progesterone (P4) from corpus luteum (CL), pregnancy recognition signal (interferon tau, IFNT) from the conceptus and prostaglandins secreted by the endometria affect uterine functions, and contribute to conceptus elongation, implantation and establishment of pregnancy in ruminants (Spencer et al., 2016). Conceptus signal (IFNT) and high concentrations of P4 contribute to immunological forbearance through regulating innate immune system in the uterus, peripheral immune cells and other tissues during early pregnancy in ruminants (Ott, 2020). Interferon tau, with its paracrine and endocrine actions, adjusts the maternal innate immune system and avoids conceptus rejection, and other immune regulators, such as the pattern recognition receptors, work in parallel with IFNT during early pregnancy in ruminants (Rocha et al., 2021). Pattern recognition receptors contribute to the activation of nuclear factor kappa B (NF-κB) to result in the downstream activation of innate immune responses (Heilmann et al., 2017). Nuclear factor kappa B family consists of NF-κB1 (p50), NF-κB2 (p52), RelA (p65), RelB and c-Rel that are involved in the regulation of development of the immune system, inflammation, and innate and adaptive immune responses in ABSTRACT. Normal pregnancy is characterised by a systemic immunological tolerance against foetal antigens, and the spleen contributes to the adaptive immune tolerance during pregnancy. Nuclear factor kappa B (NF-κB) signallings participate in splenic immune regulation, but it is unclear whether there are changes in NF-κB components expression in the ovine spleen during early pregnancy. The objective of this study was to explore the effects of early pregnancy on the expression of NF-κB components in the maternal spleen in sheep. The spleens were sampled on day 16 of the oestrous cycle, and on days 13, 16 and 25 of gestation. The expression of NF-κB components, including NF-κB1 (p50), NF-κB2 (p52), RelA (p65), RelB and C-Rel, were detected by quantitative real-time PCR, Western blot analysis and immunohistochemical analysis. The results showed that NF-κB1 and RelB mRNA and proteins decreased at days 13 and 16 of pregnancy, but increased at day 25 of pregnancy in comparison with that on day 16 of the oestrous cycle. Nevertheless, NF-κB2 and RelA mRNA and proteins peaked at days 13 and 16 of pregnancy. In addition, early pregnancy inhibited C-Rel expression at days 16 to 25 of pregnancy in the maternal spleen. In conclusion, the variable expression of individual NF-κB components was found in the ovine spleen during early pregnancy, which may be related with pregnancy recognition, and essential for the embryo implantation and pregnancy maintenance. Received: 30 September 2021 Revised: 25 January 2022 Accepted: 7 February 2022