Chlamydophila abortus targets the ovine placenta, causing tissue damage,
inflammation and abortion. C. abortus is the main infectious cause of abortion in
ewes in the UK and results in major economic losses to the sheep industry. A
pregnant mouse model was developed to investigate immune responses and disease
pathogenesis for comparison with the ovine disease.Pregnant mice were inoculated at mid-gestation with C. abortus to investigate
progression and pathogenesis of infection. This resulted in abortion on days 6-8 post¬
infection (p.i.). Infected cells were identified at the maternal-foetal interface on days
3 and 5 p.i. and chlamydial inclusions were scattered throughout the trophoblastic
labyrinth of the placenta between days 3 and 7 p.i.. Infected areas were accompanied
by a maternal mononuclear inflammatory cellular infiltrate, including
polymorphonuclear neutrophils, B cells and CD4 and CD8 T cells. C. abortus
organisms were cultured from both maternal and foetal tissues, higher numbers
present in placenta, the target organ.A Thl type immune response was characterised in the mouse model, similar to that
in ovine infections. A dominant IgG2a antibody response was identified and IFN-y
and TNF-a expression were detected in both sera and supernatants from stimulated
splenocytes. IFN-y mRNA and TNF-a mRNA expression were detected by in situ
hybridisation in mouse tissues infected with C. abortus. A latent/subclinical
persistent infection did not appear to develop in non-pregnant mice infected with C.
abortus and abortion did not occur in the subsequent pregnancy, in contrast to that in
ovine infections. Repeat abortion did not occur in the pregnancy subsequent to
abortion in mice, similar to the situation observed in sheep. Mice were also immune
to secondary infection in the pregnancy subsequent to abortion.Infection of pregnant mice resulted in abortion as observed in infected ewes, and a
similar Thl immune response is elicited in both sheep and mice. This model will
allow the rapid screening of novel protein and DNA based vaccines to protect against
chlamydial abortion
