A study of immunoglobulin G subclasses in patients with farmer's lung.

A quantitative estimate of the IgG subclasses in patients with farmer's lung has revealed significantly higher IgG3 levels in patients with this condition compared to an age-matched group of control farmers similarly exposed to Micropolyspora faeni (P less than 0.01) and a group of normal blood bank donors (P less than 0.001). The IgG1 and total IgG levels were significantly higher in both groups of farmers compared to blood bank controls (P less than 0.001). The possible significance of these observations is discussed in relation to susceptibility to the disease and its pathogenesis.