The role of toll like receptors in pregnancy

For many years, the innate immunity was of less interest than the adaptive immunity because it was perceived to have secondary importance in the functionality of the immune system. During the past decades, with the advancement of knowledge about innate immune system, interest in innate immunity has grown dramatically and thus its function has been extensively studied. Innate immunity plays fundamental roles in the initiation and induction of adaptive immune responses. It consists of several cells and receptors including natural killer (NK) cells, macrophages (MQs), dendritic cells (DCs) and pattern recognition receptors (PRRs). Two decades ago, Toll like receptors (TLRs) family was known as one of the important PRRs with unique functions especially in protection against invading pathogens. Since the female reproductive tract has access to the outside environment and has a unique interaction with different pathogens whether invading microorganisms or normal flora, allogenic sperm and semi allogenic fetus, it has an essential need for effective immune responses. It has therefore been suggested that TLRs may play important roles in the immune regulation of the female reproductive tract. In addition, it has been demonstrated that immune disturbance may be responsible for some adverse pregnancy outcomes such as preeclampsia (PE), recurrent spontaneous abortion (RSA) and intrauterine growth restriction (IUGR). Our focus in this review is to show the importance of TLRs in pregnancy with emphasis on the expression of these receptors in different tissues related to pregnancy.