RESUMO
Exposure of the immune system to environmental antigens and infectious agents by way of the anal mucosa and perianal skin could play an important role in protecting the respiratory tract against allergic conditions and virus infections. Hygienic practices that have reduced exposure of the immune system to such agents include the use of modern toiletry, disposable diapers and clothes dryers. Historically, the anal region was cleansed following defecation with natural materials that would have brought antigens and infectious agents from the environment into frequent contact with the perianal skin and anal mucosa. This practice was a crude form of transcutaneous and mucosal vaccination, whereby antigenic agents that are topically applied to skin or mucosal surfaces, penetrate into the tissues and stimulate immune responses that can extend to the respiratory tract. Furthermore, until the 1960s, diapers and other cloth items were often dried outdoors where they would have collected environmental antigens that, when applied to the body, could have made contact with the immune system in the skin. Herein, it is hypothesized that prevention of allergic rhinitis and possibly other disorders involving the immune system could be achieved by the daily application of preparations composed of environmental antigens and infectious agents to the anal mucosa and adjacent skin. In support of the proposal, immunotherapy for allergic rhinitis currently involves administration of specific allergens to subcutaneous tissue or to the sublingual mucosa. It is considered that superior protection could be achieved by applying the allergens to the anal region where they would target the immune system in both mucosal tissue and adjacent skin. It is also hypothesized that respiratory viruses applied to the anal region would infect tissues at that site and induce immune responses that would protect the respiratory tract against the common cold and influenza. This approach is supported by evidence that orally administered adenovirus vaccine can induce an infection in the intestinal mucosa that stimulates immunity to protect the respiratory tract. Although other respiratory viruses are unlikely to survive passage through the intestinal tract, rhinovirus has on rare occasion been detected in stool specimens, suggesting the possibility of an infection at the terminal end of the digestive tract. Respiratory syncytial viruses and influenza viruses are amenable to modification by reverse genetics and other techniques and it is expected that natural or modified viruses applied to the anal region could serve to immunize the respiratory tract.