RBC-associated IgG in patients with visceral leishmaniasis (kala-azar): a prospective analysis.
BACKGROUND
Despite the fact that anemia is one of the most striking clinical features of visceral leishmaniasis (kala-azar), the factors involved in its pathogenesis are not fully understood. Although the cause of the anemia seen in these patients is often multifactorial, sequestration and destruction of the RBCs in the enlarged spleen, immune mechanisms, and alterations in RBC membrane permeability have been implicated.


METHODS
To investigate whether RBCs of patients with kala-azar were coated with IgG, blood samples of 67 patients were tested, prospectively, before (Day 1), during (Day 30), and after (Day 90) antimonial therapy, to examine the presence of RBC-associated IgG, circulating immune complexes (CICs), and rheumatoid factor (RF).


RESULTS
The prevalence of a positive DAT on Day 1 was significantly greater than the prevalence of a positive DAT performed on Day 30 and on Day 90 (32.8 vs. 4 vs. 0%, p < 0.001). With an enzyme-linked antiglobulin test (ELAT) to measure the number of IgG molecules per RBC more accurately, it was found that the amount of IgG molecules per RBC was increased (mean, 298 molecules of IgG per RBC) in the group of patients with kala-azar tested before antimonial therapy, but was considered normal (<50 molecules of IgG per RBC) in all patients tested 90 days after treatment. The prevalence of a positive eluate test was low (15.0%) in DAT (anti-IgG)-positive patients and the positivity of DATs and ELATs correlated with the presence of either RF or CICs, respectively.


CONCLUSIONS
These data suggest that a nonspecific adsorption of CICs on the RBC surface is probably the most important factor involved in the increased amount of RBC-associated IgG in patients with untreated visceral leishmaniasis; however, further prospective studies are required to establish the exact role of the RBC-associated antibodies, CICs, and RF as contributing factors of the anemia seen in these patients.
Vilela
Rosana B
RB
Department of Medicine, Federal University of Alagoas, Maceió, AL, Brazil.
Bordin
José O
JO
Chiba
Akemi K
AK
Castelo
Adauto
A
Barbosa
Maria C
MC
D000740:Anemia / Q000097:blood / Q000209:etiology*; D000744:Anemia, Hemolytic, Autoimmune / Q000097:blood; D000918:Antibody Specificity; D000965:Antimony / Q000627:therapeutic use; D003298:Coombs Test; D004912:Erythrocytes / Q000276:immunology*; D006386:Hemagglutination Tests; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D007898:Leishmaniasis, Visceral / Q000097:blood* / Q000150:complications / Q000188:drug therapy / Q000276:immunology; D008107:Liver Diseases / Q000097:blood; D011446:Prospective Studies
D007074:Immunoglobulin G; D000965:Antimony