Total white blood cell counts and LPS-induced TNFα production by monocytes of pregnant, pseudopregnant and cyclic rats

Pregnancy in the rat may be associated with an activated innate immune system. Therefore, we investigated monocyte function as well as total white blood cell (WBC) counts during the follicular phase of the ovarian cycle, pregnancy and pseudopregnancy in the rat. Rats were equipped with a permanent jugular vein cannula, and 0.43 ml blood samples were taken from this cannula during the 4 days of the regular oestrus cycle of the rat ( n=12). Thereafter, six rats were rendered pregnant, and the other six rats were rendered pseudopregnant according to standard methods. Blood samples were withdrawn from the cannula on days 4, 7 and 11 of pseudopregnancy and on days 4, 7, 11 and 20 of pregnancy. From each blood sample, 0.4 ml was stimulated with lipopolysaccharide (LPS) and monocyte intracellular cytokine production measured using flow cytometry. 30 μl of the blood was used to measure WBC counts and differential WBC counts. The results showed that the number of WBC was significantly increased only on day 11 of pregnancy compared with the follicular phase, and that this was due to the increased numbers of polymorphonuclear (PMN) cells. The percentage of TNFα-producing monocytes was increased on all days of pseudopregnancy and on day 11 of pregnancy. The fact that the percentage of monocytes producing TNFα upon an LPS stimulus was increased during the post-implantation phase of pregnancy and during pseudopregnancy as compared to the follicular phase may indicate that these conditions are proinflammatory conditions. For the post-implantation phase of pregnancy, this is once more stressed by the increased numbers of WBC and PMN.