FRI0597 IMMUNOGLOBULIN A FOR CD74 AS AN ALTERNATIVE LABORATORY MARKER FOR DETERMINING THE ACTIVITY OF AXIAL SPONDYLOARTHRITIS
Authors: E. Vasilenko, V. Mazurov, S. Lapin, I. Kholopova, A. Dadalova, I. Gaydukova
Journal: Annals of the Rheumatic Diseases (2020)

Background: The level of acute phase indicators does not always correspond to the activity of axial spondyloarthritis (axSpA). The level of C-reactive protein (CRP) is remain normal in a third of cases of axSpA with present of active clinical symptoms [1]. Search for new biomarker that should have increased sensitivity and specificity compared to the CRP is needed. An alternative biomarker of axSpA activity could be an immunoglobulin (Ig) A antibody to an invariant chain peptide associated with class II human leukocyte antigen (HLA) (anti-CD74) [2]. Objectives: is to determine the level of IgA anti-CD74 in patients with axSpA and its relationship with traditional indicators of disease activity. Methods: Totally, 137 patients with a reliable diagnosis of axial spondylitis (ASAS criteria, 2009) and 47 healthy volunteers were involved in the study. AxSpA activity indices (ASDAS, BASDAI) were calculated for all patients and IgA levels of anti-CD74, ESR and CRP were determined. The normal level according to the instructions for the laboratory kit for determining the level of IgA anti-CD74 is 12.0 U/L. Results: Patients and volunteers characteristics are present in Table 1. Table 1. Characteristic of the patients with axial spondyloarthritis (n=137) and healthy volunteers (n=47) Indicator Results AxSpA patients Healthy volunteers Male, n (%) 101 (73.7) 19 (40.4) Age, years (mean±SD) 43.4±13.3 49.0±11.0 Disease duration, years (mean±SD) 12.6±8.3 Activity indices ASDAS, points (mean±SD) 2.29±1.17 BASDAI, points (mean±SD) 3.02±2.0 Laboratory markers CRP, mg/L (mean±SD) 9.61±18.3 2.3±1.9 Abnormal level of CRP, n (%) 114 (83.2) 4 (8.5) IgA anti-CD74, U/L (mean±SD) (fig.1) 16.9±11.0 9.3±5.5 Abnormal level of IgA anti-CD74, n (%) 96 (70.1) 15 (31.9) ESR, mm/h (mean±SD) 24±7.8 8.5±7.9 A direct relationship was found with a high power between an increase in the level of anti-CD74 (R=0.667) and an increase in the ASDAS (R=0.857) and BASDAI (R=0.842). The factor analysis showed that an increase in activity level according to ASDAS, BASDAI indices was associated with an increase in concentration of IgA anti-CD74. While CRP indicators (R=0.530) were associated only with the ASDAS index (R=0.760) (Table 2). Table 2. Factor loads of the relationships identified between the concentration of IgA anti-CD74 and the activity indices of axial spondyloarthritis Indicator Factor loading (R) Factor Factor 1 Factor 2 Factor 3 IgA anti-CD74 - - 0.667 BASDAI - 0.844 0.842 ASDAS 0.530 0.959 0.857 BASFI - 0.614 0.820 CRP 0.760 - - «-» no significant association present. Figure. 1. Concentration of IgA anti-CD74 for healthy volunteers (left) and patients with axial spondylitis (right) As compared to controls sensitivity of IgA to anti-CD74 was 64,7%, specificity of this method was 68,1%. Conclusion: The concentration of IgA to anti-CD74 is increased in 70.1% of pts with axSpA and associated with an increase in disease activity detected with ASDAS and BASDAI, independently from CRP. More data are needed in detection of sensitivity and specificity of IgA to CD74 in axSpA. References: [1] Turina MC, et al. RMD Open. 2017;3(1):e000319. doi: 10.1136/rmdopen-2016-000319 [2] Elke Riechers, et al. Arthritis Rheumatol. 2019;71(5):729-735. doi: 10.1002/art.40777 Disclosure of Interests: Elizaveta Vasilenko: None declared, V Mazurov: None declared, Sergey Lapin: None declared, Irina Kholopova: None declared, Anna Dadalova: None declared, Inna Gaydukova Grant/research support from: JSC BIOCAD, Speakers bureau: Pfizer, Novartis, AbbVie, JSC BIOCAD, Сelgene, MSD, Sanofi