Natural killer cells, macrophages and inflammatory chemokines in recurrent pregnancy loss: Immunohistochemical study

Background: Recurrent pregnancy loss (RPL) is a common pregnancy complication and is defined as three or more consecutive pregnancies loss before the 20^th week of gestation. Immunological factors are believed to be a major cause in RPL, where natural killer (NK) cells and macrophages have a crucial role. Their presence in the endometrium at the perigestational period suggests their role in implantation, pregnancy continuation and/or complications. Objective: To study the changes of the placental/decidual immune cells in relation to RPL. Material and Methods: Placental/decidual samples were collected from 50 cases with RPL (study group) and from another 50 cases with sporadic abortion (control group). Samples were fixed in 10% neutral-buffered formalin and prepared for sections stained with markers for decidual natural killer (dNK) cells CD56, decidual macrophages (dM) CD68, and chemokines (CCL3 and CXCL12). Expression of these markers was detected by using the peroxidase labeled avidin-biotin method. Result: Our result indicated that the number of CD56 immunopositive dNK cells was increased significantly in cases of RPL (154.80 ± 81.158) compared to those of sporadic abortion (36.80 ± 16.604), P= 0009. In contrast, the optical density of the CD56+ NK cells showed no significant difference between RPL cases (0.527059632 ±0.112194276) compared to sporadic abortion cases (0.4786766 ± 0.17088177), P= 0.117. Additionally, the number of decidual CD68 immunopositive macrophages was increased significantly in cases of RPL (506.20 ± 260.522) compared to those of sporadic abortion (150.40 ± 8.532), P= 0.009. While, the optical density of the CD68+ macrophages showed no significant difference between RPL cases (0.4614744 ± 0.12156944) compared to those of sporadic abortion cases (0.4549126 ± 0.108159912). On the other hand, the number and optical density of CCL3 and CXCL12 immunopositive cells showed no difference between the two study groups. Conclusion: Decidual natural killer cells and macrophages have a crucial role in pregnancy continuation. However, great increase in their number could affect the pregnancy outcome, by unclear mechanism\s leading to RPL.