Objective: To compare immunohistochemical expression of different T type lymphocytes as well as T reg lymphocytes in foci of VUE in placentae from pregnancies complicated with PE and in foci of VUE in placentae without PE. To compare immunohistochemical expression of T reg lymphocytes and NK cells in the basal decidua, in placentae with VUE from pregnancies with and without PE and from normal pregnancies. To compare grade and number of foci between VUE in placentae from pregnancies complicated with PE and in placentae from pregnancies without PE. Material and methods: Fiftyfour placentae were collected from pregnancies who had villitis of unknown etiology with [N=27] and without [N=27] preeclampsia and twenty [N=20] from normal pregnancies. Clinical diagnosis of PE was made according to the strict criteria of hypertension and proteinuria, and diagnosis of VUE according to the presence of lymphohistiocytic infiltrate affecting varying proportions of the villous tree of the placenta. Immunohistochemistry for the number and type of T cell inflammatory infiltrate in VUE foci as well as T reg and NK cells in basal decidua was performed on formalin fixed and paraffin-embedded sections by use of the CD3, CD4, FOXP3, CD25, CD8, CD45, CD56 and CD68 antibodies. Cytomorphological characteristics of examined placentas were determined by the number of foci and grade of VUE. Results: There was no statistical difference in terms of foci and grade of VUE between VUE with and without PE. Also, there was no statistical difference in terms of parity, maternal age, birth weight, birth length and gestational age, but there was a statistical difference in terms of birth weight and gestational age between VUE with and without PE and control group. There was statistically significant difference in total CD4+ lymphocytes count, number of villi infiltrate with CD4+ lymphocytes and CD4+/CD8+ ratio between VUE with and without PE. No statistically significant difference of the total number and type of inflammatory cells and number of villi infiltrated with CD3, CD8, CD25, FOXP3, CD45 and CD68 between the study groups was detected. Analysis of T reg and NK cells infiltrate in the basal decidua among all three investigated groups revealed statistically significant difference in total CD4+ lymphocytes count between group with VUE with and without PE and with VUE with PE and control group. There was no statistically significant difference between group with VUE without PE and control group. CD25+ i FOXP3+ were negative. No statistically significant difference of the total number of decidual CD56 cells in basal decidua between the study groups was noticed. Conclusion: T reg lymphocytes expressing the CD4+, CD25+ and FOXP3+ markers were analysed for their presence and influx in VUE foci in the placentae, and were detected individually and rarely, without statistically significant between-group difference, also in decidua. Natural killer cells which were analysed in decidua were detected also individually and rarely without statistically significant between group difference. This study results revealed statistically significantly larger CD4+ T lymphocyte population and CD4+/CD8+ ratio in placentae with VUE with PE compared to VUE without PE. Future studies should include a greater sample of VUE and PE and focus on analysis of the overall CD4+ lymphocyte subpopulation and concurrent analysis of CD4+ lymphocyte subpopulation from peripheral blood collected from the same pregnant women, as these cells probably contribute to the inflammatory response and symptoms of PE, while also being relevant for proper understanding of these intriguing inflammatory lesions of human placenta. The physiology of the immune interaction between the fetus and the mother during pregnancy is an unexplored field that has received increasing attention during the past years. The understanding of immune interactions during normal pregnancy could help guide the research of pregnancy-associated disorders such as PE what would finally allow the development of effective therapeutic tools.