Elevated serum IgG4 levels in cystic fibrosis patients.

The quantitative measurement of the IgG subclass composition of the sera from 
sixteen patients with cystic fibrosis has revealed grossly elevated levels of 
IgG4 in seven patients. The possible significance of this observation is 
discussed in relation to recent reports of a high incidence of 
immediate-type hypersensitivity in such patients. 