Читать книгу Ridley's The Vulva - Группа авторов - Страница 119

The skin is an important site for antigen presentation, and intact immune surveillance is an important defence against infection. The immune response in the genital tract has a unique task as it has to balance protection from infection against tolerance to sperm, the embryo, and foetus. The innate and adaptive immune systems are influenced by hormonal changes, so in the secretory stage of the menstrual cycle, infection is a greater risk as the immune response reduces to prepare for a potential pregnancy [17].

Langerhans cells play a vital role in the skin immune system, and the vulva has the highest density and the vagina the lowest in the female genital tract [18]. This does not vary with the menstrual cycle [19], but cell‐mediated immunity reduces after menopause.

Together with vaginal microbiota, the cervical mucus is an important component of the genital immune system. It contains antibodies, in particular secretory immunoglobulin A (IgA). This locally produced antibody is bactericidal in the presence of lysozyme and complement, and can agglutinate bacteria and present them for phagocytosis. It can also reduce the adhesion of the infective agent to the mucosa.

Protection against viral infection also requires an effective cytolytic T‐lymphocyte response. Patients who are immunosuppressed secondary to primary immune deficiency or medication have a significant risk of viral infection such as human papillomavirus (HPV) and its associated oncogenic disease [20]. It has also been shown that oral contraception can reduce immune responses to infections such as HIV [21].

Large numbers of spermatozoa enter the female reproductive tract during coitus, and these are destroyed by a coital immune response which is limited by the immunosuppressive function of seminal fluid to the immediate postcoital period [22]. This ensures that the embryo, which expresses paternal alloantigens, is not subject to immune attack during implantation. Seminal fluid can also induce inflammatory cytokines after intercourse [23]. The changes in immunity throughout pregnancy are much more complex [24].