Selective immunoglobulin G4 deficiency and recurrent infections of the respiratory tract.

Using a newly developed radioimmunoassay, 4 of 422 subjects tested were found to have an isolated absence of the immunoglobulin subclass IgG4. All had severe recurrent sinopulmonary infection. The association of these disorders with an isolated absence of IgG4 suggested that this immunoglobulin subclass may have a unique role in host respiratory tract defense mechanisms.