Immunologic Defences at the Mucous Membrane

Immunologic Defences at the Mucous Membrane

Immunologic Defences at the Mucous Membrane

The skin and mucous membranes constitute the surface of the animal host and are directly accessible to contamination by microorganisms. Each surface has some means of ridding itself of microorganisms with the result that only certain specially adapted microorganisms can survive. The adapted types constitute the normal flora of the body. The metabolic activities of the normal flora play an important role in preventing the establishment of pathogenic microorganisms. Nonimmunologic anatomic factors of the respiratory gastrointestinal, and urinary tracts, and vagina also playa major role in defending the mucous surfaces against microorganism. The efficiency of these physical barriers is enhanced by the production of certain antimicrobial substances that kill certain microorganisms.

Both cellular and humoral antimicrobial mechanisms are also operative at the mucosal surface. Infected mucosal surfaces secrete specific antibodies of the IgG, IgM, IgA, the last being the most dominant. The complex of secretory IgA and its antigen can activate the properdin pathway and thus initiate opsonization in vitro. And, if both complement and lysozyme are present, it can also induce bacteriolysis. In vivo, however, IgA prevents microbial adherence to the mucosal surface. A local cell-mediated immune reaction to many mucosal pathogens is also initiated by lymphocytes, mainly T cells.

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