ROLE OF IMMUNOGLOBULIN-G SUBCLASSES IN Q-FEVER

The progression of Q fever to either acute or chronic disease has been attributed both to biological characteristics of the bacteria and to the host immune response. In order to determine whether a specific imm unoglobulin G (IgG) subclass distribution could play a diagnostic or p rognostic role in Q fever, IgG subclass levels were measured in patien ts with acute or chronic disease. It was observed that (i) IgG1 and Ig G3 levels were elevated in patients with chronic Q fever compared to p atients with acute disease or normal controls; (ii) variations over ti me reflected inverse complementary relationships of subclass levels, s uch as between IgG1 and IgG3 compared with IgG2 and IgG4, or an invers e relationship between IgG1 and IgG2; (iii) variations in IgG2 and IgG 3 total subclass levels during follow-up of patients with chronic Q fe ver showed a decrease in IgG2 with a concomitant increase in IgG3 two years from disease onset. These findings indicate that measurements of IgG subclasses may be a simple, additional tool useful in the diagnos is of Q fever. This data raises the question of an unusual immunoregul atory mechanism in Q fever that is implicated in the presentation of t he clinical disease.