booster immunization in serum and in the vaginal secretions. Rüttgers identified mucosal secretory IgA as a strong immune correlate of vaccine efficacy. Humoral immune response Mucosal surfaces are a major portal of entry for pathogens into the body. Antibodies in mucosal secretions represent the first line of immune defense of the mucosae. They are capable to bind to specific pathogens and prevent their adherence to the epithelial cell lining of the mucous membranes. Neutralized pathogens can then be eliminated from the mucosal surfaces by means of conveyance by the mucus stream. Mucosae throughout the body have been described as parts of a common mucosal immune system (CMIS). The basis for this concept is the observation that precursor lymphocytes sensitized to a certain antigen at a specific mucosal site can migrate and assume effector function at distant mucosal tissues. Although the female genital tract is thought of as part of the CMIS, it shows some characteristics that set it apart from other mucosal immune sites. One of these features is the relative inefficacy of local antigenic stimulation owing to a sparsity of mucosal lymphoepithelial inductive sites. A further distinctive characteristic is the significant contribution of the systemic immune compartment to the pool of antibodies. In most external secretions, like tears, saliva or milk, the dominant antibody class is secretory IgA (sIgA), whereas in the cervicovaginal secretions IgG levels equal or exceed the levels of sIgA. A large portion of this IgG is thought to originate from the circulation and appear in vaginal fluids via transudation through the uterine tissues. There are reports that systemic immunization can stimulate humoral immune protection in vaginal secretions more efficiently than in other mucosal secretions, where serum-derived IgG concentrations remain lower. Milovanović and coworkers studied the serum antibody response of 97 women with trichomonad colpitis to primary immunization with SolcoTrichovac (3 intramuscular injections of 0.5 ml vaccine at intervals of 2 weeks) and a booster dose of 0.5 ml administered 12 months after the first injection. The agglutination titres were determined by preparing two-fold serial dilutions of the serum samples in isotonic saline (dilutions of 1:10 to 1:1280), using 0.5 ml concentrated lactobacillus vaccine as an agglutinogen. An at least threefold elevation of the agglutination titres following primary immunization was detected in the serum of 93.8% of patients; the rest of the patients were considered non-responders or poor responders to the vaccination. The geometric mean of