High prevalence of rheumatoid factor associated with clinical manifestations of rheumatic disease in Kaingang and Guarani Indians from Southern Brazil

The aim of the present study was to perform a screening for rheumatoid factor (RF) and anti-nuclear antibody in Kaingang, Guarani and Mestizos individuals from Mangueirinha Reservation, State of Paraná, Brazil, and associate it with demographic and clinical data. Serum samples from 321 aborigines (125♂ and 196♀; 4–86 years old) and 180 non-Indians healthy individuals were analysed (62♂ and 118♀; 2–81 years old). Antinuclear antibody (ANA) was tested by indirect immunofluorescence, and RF by agglutination in latex and turbidimetry. RF was higher in Kaingang when compared to Guarani (P = 0.009), Mestizos (P = 0.061) and non-Indians (P = 0.010). A significant increase of RF was observed in Kaingang women versus Kaingang men (P = 0.002) and, among the women, in Kaingang when compared to Mestizos and Guarani (P ≤ 0.008). The positivity for ANA did not show significant differences between the groups. Clinical evaluation of RF positive individuals (n = 6) confirmed rheumatoid arthritis in two Kaingang Indians. Other two individuals (RF positive) will be under medical observation, as well as two Mestizos. The differences observed among the investigated groups, suggest the influence of genetic and hormonal factors in the development of auto antibodies in these populations.