Editorial [Hot Topic: Recent Developments in Adaptive and Innate Mechanisms of Mucosal Immunity (Executive Editor: Pearay L. Ogra)]

During the past five decades, there has been a remarkable growth of knowledge in the areas of cellular and molecular biology and in the development of mucosal immune responses to infectious agents, dietary antigens and other environmental macromolecules. The recognition of lymphoid tissue in the gastrointestinal tract and the discovery of IgA in the serum with subsequent identification of secretory IgA molecule in the external body fluids was followed by extensive characterization and the biologic functions of the immunoglobulin isotypes in external secretions, especially of secretory IgA. Subsequent studies have clearly identified the existence of a common mucosal immune system, especially on the peripheral mucosal surfaces of the gastrointestinal and respiratory tract mucosa, and the distant mucosal sites such as male and female genital tracts, ocular tissue, salivary glands and the mammary glands and the products of lactation. Although we have come a long way in identifying the mechanisms of immunity in the mucosal surfaces and their role in mucosal immunologic homeostasis, the role of mucosal immunity in the prevention of infectious or immunologically mediated disease process remains to be defined. It is clear that mucosal immune mechanisms exhibit considerable functional diversity, ranging from, modifying the outcome or prevention of mucosally acquired infections, specific neutralization of viruses; and bacterial toxins and generation of a number of proinflammatory or immunoregulatory cytokines or chemokines. More recent studies have suggested that several elements of mucosal immunity especially those related to pathogen recognition receptors and other aspects of innate immunity at the mucosal surfaces may play a critical role in regulation of the immune response and in determining the outcome of auto-immune disease states. This special issue of the journal is devoted in part to the recent developments in the molecular and cellular aspects of mucosal immunity and the common mucosal immune system. Ponda and Mayer provide a very brief overview of the innate and adaptive immune system with a special emphasis on mucosal epithelium. Its role in antigen presentation, processing and co-stimulating signaling is discussed. This is followed by a comprehensive discussion by Kunisawa, et al. on the structural and functional characteristics of mucosalassociated lymphoid tissue in the respiratory and intestinal tracts. The review by Vliagoftis and Befus has provided an in depth analysis of the role of mast cells as major effectors of IgE mediated mucosal inflammation. Their role in the diverse physiologic and pathologic states relative to innate and adoptive mechanisms are also discussed. One of the most remarkable success stories of modern medicine is the control of many infectious diseases through the use of vaccines and the role of mucosal immunity in prevention of disease or reinfection. A number of approaches have been considered for amplifying mucosal immune response, including mucosal immunization, use of adjuvants and immunization via transcutaneous routes. The review by Professor Lycke explores targeted use of vaccine adjuvants based on modified cholera toxin. Finally, Hickey et al. have summarized new approaches to the induction of mucosal immunity notably by transcutaneous immunization.