The cell-mediated immune response to Neospora caninum during pregnancy in the mouse is associated with a bias towards production of interleukin-4

Neospora caninum is an obligate intracellular protozoan parasite which is efficiently transmitted transplacentally in cattle where it may cause abortion. A pregnant mouse model was used to characterise the immune response following N. caninum infection; the response in non-pregnant and pregnant mice was compared. Spleen cells from both infected/non-pregnant and infected/pregnant mice produced interferon-gamma, interleukin-12 and tumour necrosis factor alpha; however, the levels of these Th1 cytokines were lower in infected/pregnant mice. Infected/non-pregnant and infected/pregnant mice also produced the Th2 cytokine interleukin-10; however, there was no trend toward a decrease of this in pregnant mice. Interleukin-4 was exclusively produced at high levels by infected/pregnant mice and thus appears responsible for the observed decline in Th1 cytokine production in pregnant mice. A bias towards Th2 cytokines such as IL-4 and IL-10 is normally associated with the maintenance of a viable pregnancy, and not with the control of protozoal infections. Consequently, the importance and role of cytokines and cell-mediated immunity in the control of transplacental transmission and foetal loss due to N. caninum infection are discussed.