High IgA antiphospholipid autoantibodies in healthy Sudanese explain the increased prevalence among Sudanese compared to Swedish systemic lupus erythematosus patients

• Published in: Lupus 2020-10, Vol.29 (11), p.1412-1422
• Main Authors: Elbagir, Sahwa, Elshafie, Amir I, Elagib, Elnour M, Mohammed, NasrEldeen A, Aledrissy, Mawahib IE, Manivel, Vivek Anand, Pertsinidou, Eleftheria, Nur, Musa AM, Gunnarsson, Iva, Svenungsson, Elisabet, Rönnelid, Johan
• Format: Article
• Language: English
• Subjects: Africa; anti-beta 2-glycoprotein I; Antiphospholipid antibodies; Antiphospholipid syndrome; Autoantibodies; Cardiolipin; Fetuses; Glycoprotein I; IgA; Immunoglobulin A; Immunoglobulin G; Isotypes; Lupus; Medicin och hälsovetenskap; Population studies; Sudan; Sweden; Systemic lupus erythematosus
• ISSN: 0961-2033; 1477-0962; 1477-0962
• DOI: 10.1177/0961203320945387

Objectives IgA antiphospholipid antibodies (aPL) are prevalent in systemic lupus erythematosus (SLE) patients of African American, Afro-Caribbean and South African origin. Nevertheless, data from North Africa are lacking, and most studies use manufacturer-suggested cut-offs based on Caucasian controls. Therefore, we compared aPL isotypes in Sudanese and Swedish SLE patients using nation-based cut-offs. Methods Consecutive SLE patients and age- and sex-matched controls from Sudan (N = 115/106) and Sweden (N = 340/318) were included. All patients fulfilled the 1982 American College of Rheumatology SLE classification criteria. Antiphospholipid syndrome–related events were obtained from patients’ records. IgA/G/M anticardiolipin and anti-β2 glycoprotein I (β2GPI) were analysed with two independent assays. IgA anti-β2GPI domain 1 (D1) was also investigated. Manufacturers’ cut-offs and the 95th and 99th percentile cut-offs based on national controls were used. Results Sudanese patients and controls had higher levels and were more often positive for IgA aPL than Swedes when using manufacturers’ cut-offs. In contrast, using national cut-offs, the increase in IgA aPL among Sudanese patients was lost. Occurrence of IgA anti-D1 did not differ between the countries. Venous thromboses were less common among Sudanese patients and did not associate with aPL. No clinical associations were observed with IgA anti-β2GPI in Sudanese patients. Thromboses in Swedes were associated with IgG/M aPL. Fetal loss was associated with aPL in both cohorts. Conclusions IgA anti-β2GPI prevalence was higher among Sudanese compared to Swedish patients when manufacturers’ cut-offs were used. This situation was reversed when applying national cut-offs. Anti-D1 was not increased in Sudanese patients. Previous studies on populations of African origin, which demonstrate a high prevalence of IgA aPL positivity, should be re-evaluated using a similar cut-off approach.