Immunoglobulin responses in acute Q fever

Area of Science:

• Immunology
• Infectious Diseases
• Microbiology

Background:

• Accurate interpretation of serological tests for Q fever relies on understanding antibody class development.
• Coxiella burnetii exhibits distinct phase I and phase II antigens, eliciting different antibody responses.

Purpose of the Study:

• To characterize the temporal development of antibodies targeting Coxiella burnetii phases I and II in patients with acute Q fever.
• To compare the sensitivity and antibody profiles generated by complement fixation and immunofluorescence tests.

Main Methods:

• Analysis of 683 serum samples from 191 patients diagnosed with symptomatic Q fever.
• Utilized complement fixation tests and indirect immunofluorescence assays for immunoglobulins M and G (IgM, IgG).
• Sera were collected over a 1-year period following an epidemic of acute Q fever.

Main Results:

• Antibodies to C. burnetii phase II remained elevated throughout the 1-year study period, while phase I antibodies were minimally detected.
• Immunofluorescence testing demonstrated higher sensitivity than complement fixation, but IgG antibody profiles for both phases were similar.
• IgM antibodies against both phase I and II appeared early but declined within 10-12 weeks, with anti-phase II levels consistently higher than anti-phase I levels.

Conclusions:

• Distinct antibody profiles emerge for C. burnetii phases I and II during acute Q fever.
• Phase II antibodies, particularly IgG, demonstrate greater persistence than phase I antibodies.
• IgM responses are transient, highlighting the importance of IgG over time for diagnosing Q fever.