Exp Clin Endocrinol Diabetes 2007; 115 - OR08_5
DOI: 10.1055/s-2007-972249

Is the complement system activated in the bovine uterus during early pregnancy?

SE Ulbrich 1, A Hammerle-Fickinger 1, S Bauersachs 2, E Wolf 2, HHD Meyer 1
  • 1Technical University of Munich, Physiology-Weihenstephan, Freising, Germany
  • 2Ludwig-Maximilians University, Institute of Molecular Animal Breeding and Biotechnology, and Laboratory for Functional Genome Analysis (LAFUGA), Gene Center, Munich, Germany

Objectives: The complement system is an effective host defense mechanism recognizing pathogens and antibody-antigen complexes on non-innate cell surfaces. During early embryo-maternal communication the embryo resists rejection due to immunohistoincompatibility. In this study the effect of the conceptus on the expression of key factors of the complement system in the bovine endometrium during the peri-implantation period was analyzed.

Methods: Five homozygous twin cow pairs generated by embryo splitting were cycle synchronized. On day 7 of the estrous cycle, two embryos produced by IVF were transferred into the ipsilateral uterus horn of one animal, while the corresponding control twin received a mock-transfer. On day 18 the animals were slaughtered and RNA was extracted from intercaruncular endometrial samples of the ipsilateral uterine horn for quantitative RT-PCR.

Results: Transcript levels of the components of the classical pathway C1R and C1S, C2, C4 and C3 were elevated in pregnant endometrium, while only SERPING1 inhibiting C1 was differently expressed. Because neither carboxypetidase N, CFI, CFH nor the regulatory factors CR1, DAF, and MCP were upregulated, the endometrium did not express key regulatory factors inhibiting the further complement activation. However, transcripts for terminal factors C5 and C9 were not differentially expressed, therefore a membrane attack complex was not generated. These hypotheses need to be confirmed on the protein level. In pregnant animals complement receptor C3AR mRNA was increased, supposing an effect on cytokines via binding of the anaphylatoxin C3A and activation of the G-protein coupled receptor. Immunostaining of C3AR protein will verify these results.

Conclusions: This study demonstrates that maternal cells of the bovine endometrium recognize the embryo with respect to the activation of the classical pathway of the complement system. The fate of the embryo might be dependent upon the expression of regulatory factors for defense from the complement attack of the mother.