Secretory mucosal immune mechanisms.

Mucosal immune mechanisms in the airways are the first specific line of defense, protecting the body from pathogens. The respiratory epithelium actively transports locally produced dimeric IgA in the respiratory secretions by transcytosis, through the pIgR. S-IgA production therefore requires epithelial integrity. S-IgA at the epithelial level is active in several non-inflammatory pathways including intracellular neutralization of virus, antigen excretion, binding to bacterial adhesins. Local IgA production is regulated by various growth factors and cytokines of both epithelial and non-epithelial origin. The respiratory epithelium is thought to play a crucial role in this process. In addition, in chronic airway inflammation, IgA production demonstrates a correlation with eosinophil activation both in vitro and in vivo. While increased IgA and S-IgA production is reported in asthmatics, decreased SC production has been documented in CF and COPD patients, further impairing their local defense mechanisms.