Immunodiagnostic significance of anti-RA33 autoantibodies in Saudi patients with rheumatoid arthritis

Anti-RA33 Antibodies Are Present in Patients With Lyme Disease

BACKGROUND/OBJECTIVE

To determine if anti-RA33 antibodies, which can be seen in early forms of inflammatory arthritis, are present in patients with Lyme arthritis (LA).

METHODS

Anti-RA33 antibodies were tested using a commercially available assay in patients with LA (n = 47) and compared with patients with erythema migrans who returned to health (EM RTH, n = 20) and those with post-treatment Lyme disease (PTLD) (n = 50), characterized by noninflammatory arthralgia, as an observational comparative study utilizing Lyme-exposed patients from various original cohorts.

RESULTS

We found that anti-RA33 was present in higher proportions of patients with LA (23.4% vs. 0%, p = 0.001) and PTLD (12.0% vs. 0%, p = 0.040) than healthy controls. There was also a trend toward a higher percentage of anti-RA33 positivity in patients with EM RTH versus controls (10.0% vs. 0%, p = 0.080). There were no statistically significant differences among groups of patients with LA, PTLD, and EM RTH ( p ≥ 0.567). There was also no difference in the proportion of patients with antibiotic-responsive LA compared with those with persistent synovitis after antibiotics, termed post-infectious LA, and there were no differences in clinical manifestations, musculoskeletal ultrasound evaluation (synovial hypertrophy, power Doppler, tendinopathy), or patient-reported outcomes based on anti-RA33 status.

CONCLUSIONS

This is the first study to identify anti-RA33 antibodies in patients with LA, though these antibodies did not identify a unique clinical subset of patients in this cohort. Unexpectedly, we found anti-RA33 antibodies at similar levels in patients with PTLD and EM RTH; further study is needed to determine the relevance of this finding.

Anti-RA33 antibodies are present in a subset of patients with immune checkpoint inhibitor-induced inflammatory arthritis

OBJECTIVE

Patients with inflammatory arthritis (IA) associated with immune checkpoint inhibitor (ICI) treatment for cancer are typically seronegative for anti-cyclic citrullinated peptide (CCP) antibodies and rheumatoid factor, but little is known about the presence of other autoantibodies in this patient population. We investigated the prevalence and characteristics of anti-RA33 antibodies in patients with ICI-induced IA.

METHODS

Anti-RA33 ELISAs were performed on sera from four groups of patients: 79 with ICI-induced IA, 52 with rheumatoid arthritis (RA), 35 treated with ICIs without IA during follow-up and 50 healthy controls. Anti-RA33 positivity and level, clinical and demographic data were compared across groups.

RESULTS

Anti-RA33 antibodies were found in 9/79 (11.4%) patients with ICI-induced IA but in 0/35 patients treated with ICIs who did not develop IA (0%; p=0.04). Of the patients positive for anti-RA33, two had sera available from before ICI treatment; anti-RA33 antibodies were present in both pre-ICI treatments. In patients with RA, 7.7% were positive for anti-RA33 antibodies as were 2% of healthy controls. In ICI-induced IA, anti-RA33 antibodies were associated with anti-CCP antibodies (p=0.001). We found no statistically significant differences in other clinical characteristics in those with and without anti-RA33 antibodies.

CONCLUSIONS

Anti-RA33 antibodies are present in a subset of patients with ICI-induced IA, absent in other ICI-treated patients and may be a biomarker for developing IA. Additional studies evaluating serial samples before and after ICI treatment will further establish the temporal relationship of these antibodies to IA development.

Diagnostic accuracy of anti-Sa and anti-RA33 antibodies in rheumatoid arthritis: a meta-analysis

OBJECTIVE

This study evaluated the diagnostic accuracy of anti-Sa and anti-RA33 antibodies in rheumatoid arthritis (RA).

METHODS

PubMed, Embase, and Cochrane library databases were searched for relevant studies, and 2 meta-analyses were performed to determine the diagnostic accuracy of anti-Sa and anti-RA33 antibodies in patients with RA.

RESULTS

The meta-analysis included 17 studies. Pooled sensitivity and specificity of anti-Sa antibody were 39.5 % (95 % confidence interval [CI] 36.5-42.4) and 96.8 % (95 % CI 95.9-97.4), respectively, and those of anti-RA33 antibody were 31.8 % (95 % CI 28.7-35.0) and 90.1 % (95 % CI 87.8-92.1), respectively. PLR, NLR, and DOR of anti-Sa antibody were 14.11 (95 % CI 7.076-28.13), 0.607 (95 % CI 0.558-0.703), and 22.76 (95 % C, 11.10-46.69), respectively, and those of anti-RA33 antibody were 3.429 (95 % CI 2.039-5.765), 0.761 (95 % CI 0.681-0.851), and 4.597 (95 % CI 2.602-8.121), respectively. AUC and Q^* index for anti-Sa antibody were 0.558 and 0.543, respectively, while those for anti-RA33 antibody were 0.501 and 0.500, respectively.

CONCLUSIONS

Our meta-analysis indicated that both anti-Sa and anti-RA33 antibodies were highly specific but not sensitive for diagnosing RA.