Development of local immunity: role in mechanisms of protection against or pathogenesis of respiratory syncytial viral infections.

The bronchus associated lymphoid tissue (BALT) and the precursor immunocompetent lymphoid cells in the nasopharynx, tonsils, and salivary glands represent the basic source of specific secretory IgA, other immunoglobulin, and T cell mediated specific immunity in the respiratory tract. The bulk of this immunologic reactivity is derived largely from BALT, and via the migration of antigen-sensitized immunocompetent cells, from the gut associated lymphoid tissues (GALT). Recent investigations have suggested that mechanisms underlying the development of virus-induced bronchopulmonary diseases, notably bronchospasm, include host factors such as altered immune response with persistent virus-specific IgE and IgG4 antibody responses in the respiratory tract, the appearance of specific immune complexes, and development of exaggerated immune response to other environmental agents and dietary proteins. In addition, pathogen related factors responsible for direct tissue damage during infection also play an important role.