IgA anticardiolipin and anti-β2-glycoprotein I are the most prevalent isotypes in African American patients with systemic lupus erythematosus

Background: Ethnicity plays a role in the prevalence, isotype distribution, and clinical significance of anticardiolipin (aCL) and anti-beta(2)-glycoprotein I (anti-beta(2)-GPI) antibodies in patients with systemic lupus erythematosus (SLE). Few studies have been done in the African American population. Methods: Serum samples from 100 African American patients with SLE were tested for IgG, IgM, and IgA aCL and anti-beta(2)-GPI antibodies by enzyme-linked immunosorbent assay (ELISA). Computerized clinical data on these patients were reviewed with a specific focus on clinical manifestations of antiphospholipid syndrome (APS). Results: Positivity for at least one isotype of aCL antibodies was found in 33% of the patients, whereas 28% were positive for at least one isotype of anti-beta(2)-GPI antibodies. IgA was the most prevalent isotype for both antibodies; 24% of the patients in the aCL ELISA and 19% in the anti-beta(2)-GPI ELISA were positive for IgA. Positivity for both aCL and anti-beta(2)-GPI in the same patient was seen more frequently with the IgA isotype. Fewer than half of the patients positive for aCL antibodies had medium-to-high levels of antibodies. A few patients had presented thrombotic manifestations, and these patients were positive for aCL (P = 0.01) and anti-beta(2)-GPI antibodies (P = 0.02). No other manifestations of APS could be significantly correlated with the presence of these antibodies. Conclusions: Our results show that IgA is the most prevalent isotype among the African American patients with SLE studied. The predominance of the IgA isotype and the low prevalence of medium-to-high levels of aCL antibodies may account for the low frequency of clinical manifestations of APS in these patients.