Neutrophils in the female reproductive tract: immune interactions and sperm adaptations

Human fertilization is a coordinated process involving interaction of sperm with the oocyte. As the sperm pass through the female reproductive tract (FRT), they are presented with numerous challenges. These include navigating through highly viscous cervical mucus while evading immune responses to successfully fertilize the oocyte. The female immune system facilitates sperm selection while providing protection against pathogens. Neutrophils, a major component of the innate immune system, use mechanisms such as phagocytosis, neutrophil extracellular trap formation, and trogocytosis to play a crucial role in this process. With the help of sialic acid residues and N glycans present on its glycocalyx as well as certain proteins in the seminal plasma, the sperm modulate the immune responses in the FRT to their advantage. This review examines the various interactions which take place between the sperm and the FRT, the neutrophil-mediated immune reaction occurring in the FRT, as well as the adaptations the sperm employ to overcome the immune challenges. Understanding these mechanisms provides critical insights into fertility and potential therapeutic targets for infertility.