LPS-induced murine abortions require C5 but not C3, and are prevented by upregulating expression of the CD200 tolerance signaling molecule.

PROBLEM: Lipopolysaccharide (LPS) acts via tlr4 to promote Th1 cytokine secretion and abortions. LPS is an essential co-factor in spontaneous abortion in the CBA x DBA/2 model and in stress-triggered abortions. In the CBA x DBA/2 model, C3a, C5a, and fgl2 prothrombinase participate in triggering inflammation that terminates embryo viability. As fgl2 prothrombinase (via thrombin) can generate C5a, it was predicted that LPS-driven abortions (which require fgl2) would be independent of C3. CD200Fc can prevent abortions in the CBA x DBA/2 model, but an action through Fc could not be excluded.

METHOD OF STUDY: C3(-/-) and C5(-/-) knock-out mice on a B6 background were syngeneically mated and Salmonella enteritidis LPS was administered i.p. on day 6.5 or pregnancy along with 2 mg progesterone in sesame oil s.c. The total number of implants and the number of resorbing embryos were counted on day 13.5 of pregnancy. CD200-rtTA double transgenic homozygous males (B6 background) mated with B6(+/+) females were similarly treated. To up-regulate CD200 expression in embryonic trophoblasts, doxycycline was added to the drinking water from the time of mating.

RESULTS

The LPS boosted the abortion rate from 15.5% (control) to 42.0% in C3(-/-) mice (chi(2) = 9.28, P < 0.005). In C5(-/-) mice, there was no increase in abortion rate with LPS compared to progesterone-treated controls (22.8%versus 26.3%, P = NS). LPS-treated transgenic mice given LPS + progesterone had a 42.5% abortion rate, but when the mice were given doxycycline to induce expression of CD200 by the embryo, the abortion rate was only 8.3% (chi(2) = 14.40, P < 0.005, Fisher's exact test P = 0.00007).

CONCLUSION

C5, but not C3, appears necessary for LPS-driven abortions. Up-regulation of CD200 can prevent LPS-driven abortions, possibly by altering dendritic cells to promote Treg cell development or by a direct suppressive action on macrophages and mast cells that also express CD200 receptors.