Humoral immune defense (antibodies): recent advances.

The humoral, or antibody, immune response is essential for host defense against bacterial pathogens. The lung has the ability to respond quickly to some pathogens through stimulation of resident antigen-specific memory B cells. Alternatively, after exposure to a new pathogen, the lung can generate de novo both a systemic and local (mucosal) antibody response. The resulting production of antigen-specific IgG and IgA act in concert to help clear the invading pathogen and reduce subsequent colonization of respiratory epithelium. Systemic vaccination against respiratory pathogens, although effective in generating systemic IgG responses and some mucosal IgA responses, may be less effective than vaccination through mucosal surfaces, which induce a brisk IgA and IgG response both locally and systemically depending on the site of antigen deposition. The local response is important in reducing colonization of the upper respiratory tract by pathogenic bacteria, the first step in the development of most causes of pneumonia. Future studies are needed to provide further insight on the site of pulmonary humoral host responses to bacterial challenge and optimal vaccine regimens to minimize the burden of respiratory disease caused by pathogenic bacteria.