Profiles of brucella-specific immunoglobulin G subclasses in sera of patients with acute and chronic brucellosis

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Serum specimens from patients with acute brucellosis (164), chronic brucellosis (22) and controls (75) were tested by ELISA for brucella-specific IgG, IgM, IgA and subclasses of IgG1 to 4 antibodies, Rose Bengal antigen slide agglutination (RB) and microagglutination (MA) tests. The RB and MA showed similar results and were positive in 100% and 64% of specimens from patients with acute and chronic brucellosis respectively. ELISA IgG and IgA were positive in sera from all patients with brucellosis while IgM was positive in 100% and 32% of specimens from patients with acute and chronic brucellosis respectively. Elevated IgG subclasses to brucella antigen were found in different proportions in the sera of patients with acute and chronic brucellosis. In patients with acute brucellosis, IgG1 was the predominant response (79%) followed by IgG3 (58%), IgG2 (36%) and IgG4 (14%). In contrast, IgG4 was the predominating subclass response (73%) in patients with chronic brucellosis followed by IgG1 (41%), IgG2 and IgG3 (27% each). When considering the most common elevated IgG subclasses, in each serum, either alone or in combination with each other, patients with acute brucellosis showed IgG1+IgG3 (24%), IgG1 (19%), IgG1+IgG2+IgG3 (16%) while patients with chronic brucellosis showed IgG4 (27%) and IgG1+IgG2+IgG3+IgG4 (18%). This study reveals that in addition to the difference in brucella-specific Ig class response in patients with acute (IgG, IgM, IgA) and chronic (IgG, IgA) brucellosis, the profiles of IgG subclasses are different where IgG1 predominates in the acute and IgG4 in the chronic stages of the disease.