Serological follow-up of human brucellosis by measuring IgG antibodies to lipopolysaccharide and cytoplasmic proteins of Brucella species.

A serological 2-year follow-up of 35 patients who had brucellosis with different clinical outcomes was performed. Patients were followed up by standard tube agglutination (STA) and 2-mercaptoethanol STA (2ME-STA) tests and by two enzyme-linked immunosorbent assays (ELISAs) to independently measure values of serum IgG to either lipopolysaccharide (LPS) or cytoplasmic proteins of Brucella. Whereas STA and 2ME-STA tests revealed characteristic antibody profiles for patients who recovered (group I), this was not the case for patients with persistent illness (group II) or patients with relapses (group III). On the other hand, titers measured by the 2ME-STA test were low or negative in 10 patients who had positive blood cultures. Levels of IgG antibodies to LPS and proteins in each group of patients exhibited characteristic changes. For group I, however, antibodies to proteins were better predictors of recovery, since titers reached negative values for five patients. Levels of IgG antibodies to LPS and proteins were persistently high in group II patients, and peaks in these antibody levels corresponded with relapses in group III patients. The determination of values of IgG antibodies to proteins by ELISA appears useful for the serological follow-up of patients with brucellosis.