The vast majority of infectious diseases are caused by pathogens that infect mucosal surfaces or use them as portals of entry. Mucosal immune responses are the first line of defense against these pathogens that are inhaled, ingested, or sexually transmitted. However, some agents may be able to breach these defenses, and go on to cause systemic disease. Therefore, vaccines against these agents may need to induce both mucosal and circulating immune responses for optimal protection (1-3).
The systemic and mucosal immune systems communicate, but are somewhat compartmentalized (1-3). In general, induction of immune responses via systemic immunization supports systemic responses. Under appropriate conditions, mucosal introduction of foreign substances (antigens) can induce both mucosal and systemic responses. Following oral delivery, for example, antigens or invading pathogens, which can survive the harsh acid and degradative environments encountered, may be taken up by the specialized microfold or "M" cells in the small intestine and transported to the follicle beneath known as a Peyer's patch. T- and B-cell responses to the antigen occur there, followed by migration of the immune cells to the mesenteric lymph nodes. Activated cells travel via the efferent lymphatics to the thoracic duct, where they enter the circulation and migrate to various effector sites in the gastrointestinal, respiratory, and genitourinary tracts. This "Common Mucosal Immune System" allows the seeding of both systemic and mucosal sites with memory and effector cells ready to respond to the pathogen (1-3).
From: Methods in Molecular Medicine, Vol. 42: Vaccine Adjuvants: Preparation Methods and Research Protocols Edited by: D. T. O'Hagan © Humana Press, Inc., Totowa, NJ
There is evidence for both humoral- and cell-mediated responses contributing to the control of viruses, bacteria, and parasites, and having the potential for preventive or therapeutic effects (3,4). Neutralizing antibodies can limit initial infection and pathogen spread (5-7). Cytolytic T-cell responses play an important role in control and recovery from many viral and parasitic infections (8,9). Appropriate T-helper responses are also crucial to protective immunity (10,11).
Current evidence would suggest, therefore, that antibody- and cell-mediated responses, systemically and on mucosal surfaces, would be desirable for optimal protection against most infections.
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