Uterine lymphocyte distribution and interleukin expression during early pregnancy in cows

Both the production of cytokines and the distribution of immune cells withi n the uterus change during early pregnancy. Evidence obtained mainly from m ice indicates that these changes are important for implantation and in prev enting a maternal immune response to the conceptus. The ruminant embryo als o produces interferon tau at this time, the signal for the maternal recogni tion of pregnancy. The relationship between these events in cows was studie d using uteri from three groups of animals on day 16 after observed oestrus : (i) cyclic controls, (ii) pregnant and (iii) inseminated but with no embr yo present. Embryo size and the antiviral activity in uterine flushings (in dicative of the interferon tau concentration) were measured. Sections of in tact uterus were frozen for the localization and quantitation of CD4(+) (T lymphocytes), CD14(+) (macrophages) and CD21(+) (B lymphocytes) uterine cel ls by immunohistochemistry. The expression of interleukin (IL)-1 alpha, IL- 2, IL-6 and IL-10 mRNAs in uterine extracts was measured by RT-PCR. Neither embryo size, interferon tau concentration nor pregnancy status influenced the distribution of CD4(+), CD14(+) or CD21(+) cells in the day 16 uterus. Endometrial IL-la mRNA was detected in most cows across the groups, whereas IL-2 mRNA was only present in the non-pregnant uterus. IL-6 and IL-10 mRNA s were not detectable in any uteri. In conclusion, IL-2 mRNA expression is detectable in the nonpregnant but not the pregnant uterus on day 16 and int erferon tau is unlikely to play a role in the redistribution of immune cell s in the uterus during early bovine pregnancy.