Secretory IgA and serum type IgA in nasal secretion and antibody activity against the M protein.

We studied IgA immunoglobulins in nasal secretions in order to clarify mucosal immunity of the nasal cavity and paranasal sinuses during chronic nasal infection. Secretory IgA and serum type IgA of 165 samples of nasal secretions were analyzed quantitatively by use of electroimmunodiffusion techniques, and the specific antibody activity of secretory IgA against the M protein of Streptococcus pyogenes was investigated by use of enzyme-linked immunosorbent assay. Results show that although the secretory IgA content in nasal secretions was elevated in chronic sinusitis, its specific antibody activity against the M protein was lower than that in normal subjects. This evidence suggests that nonspecific secretory IgA antibodies are predominantly produced in chronic sinusitis, and that mucosal immunity preventing the adherence of bacteria is impaired in the diseased mucosa.