AB0127 ACCUMULATION OF ANTI-NUCLEAR ASSOCIATED AUTOANTIBODIES IN CIRCULATING IMMUNE COMPLEXES IS MORE PROMINENT IN SLE PATIENTS FROM SUDAN COMPARED TO SWEDEN
Authors: S. Elbagir, A. Sohrabian, A. Elshafie, E. M. Elagib, N. A. Mohammed, M. A. M. Nur, E. Svenungsson, I. Gunnarsson, J. Rönnelid
Journal: Annals of the Rheumatic Diseases (2020)

Background: Systemic Lupus Erythematosus (SLE) is a systemic immune complex (IC)-mediated disease associated with autoantibodies targeting multiple nuclear specificities (ANA). SLE has an aggressive nature among African populations. The role of SLE-related autoantibodies in the formation of IC has only been studied to a limited extent, and not at all in African SLE patients. Objectives: To quantify ANA specificities present in circulating IC in Sudanese and Swedish SLE sera and to compare to corresponding serum levels Methods: 93 Sudanese and 337 Swedish SLE patients who fulfilled the 1982 ACR classification criteria were included. IC were captured using magnetic microparticles coated with purified human C1q, then separated by a two-step elusion procedure (Figure 1). ANA-associated autoantibodies against dsDNA, Sm, the Sm/U1RNP complex, U1RNP, SSA/Ro52, SSA/Ro60, SSB/La, ribosomal P antigen, proliferating cell nuclear antigen (PCNA) and histones were quantified in sera and corresponding IC using a bead-based multiplex immunoassay. The IC purification technique has been developed and validated in our laboratory (Sohrabian ARD 2018), and previously used to study treatment responses to belimumab in Swedish SLE patients (Sohrabian ART 2019). Occurrence of ANA specificities in serum was determined using manufacturer’s suggested cutoffs. These cutoffs were used in regression formulas to determine cutoffs for ANA levels detected in the corresponding IC. Results: Swedish patients had higher serum levels of anti-Sm, anti-dsDNA and anti-ribosomal P antibodies compared to Sudanese patients. On the contrary, IC levels of all ANA specificities except anti-SSA/Ro52 and anti-SSA/Ro60 were higher in Sudanese patients (Table 1 and Figure 2). Sudanese patients were more often positive for anti-Sm, anti- Sm/U1RNP, anti-dsDNA and anti-histone antibodies in IC, whereas a borderline statistical significance was found for only anti-Sm in corresponding serum samples (Table 1). Table 1. Levels median/mean Sudan serum Sweden serum P Sudan IC Sweden IC P SSA/Ro52 16/52.1 17/52.3 0.8 2.9/14.4 2.4/10.7 0.07 SSA/Ro60 2.0/47.2 3.0/48.7 0.2 1.5/14.6 1.3/12.5 0.7 SSB/La 2.0/22 2.0/22 0.6 1.1/4.2 0.8/5.5 0.02 Sm 1.0/21.7 1.0/11.4 0.0008 0.5/4.2 0.3/1.3 &lt;0.0001 SmRNP 1.0/20.5 1.0/16 0.2 3.7/8.6 2.0/4.6 &lt;0.0001 U1RNP 6.0/43.8 7.0/40.2 0.9 1.0/3.5 0.6/2.2 0.0005 dsDNA 14.0/124.5 28.0/198.3 0.001 32.1/50.8 12.4/25.4 &lt;0.0001 Ribosomal P 1.0/9.3 2.0/11.7 0.0006 1.7/3.3 1.4/2.9 0.005 Histone 5.0/20.5 6.0/19.3 0.2 4.0/5.9 1.9/3.4 &lt;0.0001 PCNA 5.0/8.4 5.0/8.9 0.6 11.1/14.2 7.0/11 &lt;0.0001 Occurrence n(% ) serum serum P IC IC P SSA/Ro52 30(32.2) 105(31.7) 0.9 18(19.3) 55(16.6) 0.5 SSA/Ro60 34(36.6) 122(36.9) 0.9 27(29) 89(26.8) 0.7 SSB/La 15(16.1) 64(19.3) 0.5 9(9.7) 38(11.4) 0.3 Sm 12(12.9) 21(6.3) 0.04 6(6.4) 5(1.5) 0.008 SmRNP 15(16.1) 42(12.7) 0.4 17(18.3) 33(9.9) 0.03 U1RNP 20(21.5) 69(20.8) 0.9 22(23.7) 55(16.6) 0.1 dsDNA 31(33.3) 147(44.4) 0.055 64(68.8) 105(31.6) &lt;0.0001 Ribosomal P 4(4.3) 20(6) 0.5 2(2.1) 9(2.7) 0.8 Histone 10(10.7) 34(10.3) 0.9 34(36.6) 58(17.5) &lt;0.0001 PCNA 1(1.1) 10(3) 0.3 20(21.5) 45(13.5) 0.06 Conclusion: ANA-associated autoantibodies are more accumulated in circulating IC from Sudanese than Swedish SLE patients. The clinical significance of these findings is yet to be investigated in our upcoming analyses Disclosure of Interests: None declared