Both innate and acquired host antimicrobial defense systems are operative on skin. Humoral and cell-mediated immune responses derive from Langerhans cells, keratinocytes, and endothelial cells that produce cytokines and lymphocytes. The skin-associated lymphoid tissue forms a protective barrier that can capture virtually any antigen that enters the skin. IgA and IgG antibodies are secreted by the eccrine sweat glands and are spread over the skin surface where they can exhibit antimicrobial effects and interfere with microbial adherence. The immunological factors important in the lower genital tract have been reviewed by Bulmer and Fox (18). Cervical mucus contains antibodies, in particular, secretory IgA, which are bactericidal in the presence of lysozyme and complement and can agglutinate bacteria and opsonize them for phagocytosis. Circulating antibodies to specific microorganisms can be demonstrated to result from many genital infections, but there is scant evidence of any resulting protective effect. For example, recurring episodes of chlamydial infection, genital herpes, trichomoniasis, and gonorrhea can take place in spite of high titers of circulating antibodies. Thus, a variety of immune mechanisms is operative on or in vulvar skin, but their role in shaping microbial populations is largely unknown.
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