[What is the purpose of mucosal antibodies? Relevance to colonization with group B streptococci]

The surface area of the mucosae is extremely large and its contact with the external environment is of vital importance. Most infectious agents use the mucosae as their portal of entry. Some microorganisms, however, colonize the mucosal surfaces without causing disease, and may even be beneficial by contributing to the digestion of food or by excluding pathogens. An important part of the immune system operates in the mucosae, the principal mediator substance of this local immune system being secretory IgA. Other antibody isotypes are usually found in small amounts in exocrine fluids, but IgG predominates in secretions of the uterine cervix. These mucosal antibodies may eliminate microbes, or they may coexist with persistent colonization. In a recent study, we found increased levels of IgA and IgG antibodies to group B streptococci in the cervical secretions of women colonized with these bacteria. Group B streptococci are often transmitted to the infant during delivery, and are a major cause of severe infection in newborns. We have used this study as a background for discussing the role of mucosal antibodies. Presumably, group B streptococci may be eradicated by reenforcing the local antibody response, and a mucosal vaccine will be evaluated in the near future.