Chun Lai Too, Johan Ronnelid, Yuslina Mat Yusoff, Jasbir Singh Dhaliwal, Nor Ashikin Jinah, Abqariyah Yahya, Heselynn Hussien, Wahinuddin Sulaimana, Per Tobias Larsson and Shahnaz Murad (2014). Increased IgG Rheumatoid Factor-Positivity in the Asian Rheumatoid Arthritis Patients Irrespective of Ethnicity. Open Journal of Rheumatology and Autoimmune Diseases 4(1): 43-51
Aim of Work: Initial observations implied IgG rheumatoid factor (RF) to be common among Malaysian rheumatoid arthritis (RA) patients. We tested this hypothesis and used a multiethnic RA cohort (Malays, Chinese and Indians) to investigate whether the IgG RF predominance might be genetically or environmentally determined. Patients and Methods: 556 serum samples comprising 171 patients classified as RA according to the 1987 ACR criteria, 60 patients with other rheumatic diseases and 325 non-rheumatic controls were tested for IgG RF, IgM RF and anti-CCP by ELISA. The findings were then tested in a larger RA case-control cohort (n = 1844). Results: IgG RF predominated over IgM RF in all the investigated ethnic groups. The sensitivity, specificity, and diagnostic accuracy of IgG RF (55.6%, 91.2% and 80.2%, respectively) were superior compared to IgM RF, but comparable to anti-CCP. IgG RF was however, also increased in the Malaysian controls, but the IgG RF superiority over IgM RF was still apparent after cutoff adjustment according to the 1987 ACR criteria. Autoantibody levels did not differ between the three ethnic groups. The Receiver Operating Characteristics (ROC) curves showed larger areas under the curves for IgG RF (0.826) and for anti-CCP (0.867) than for IgM RF (0.737). Review of the literature showed consistently higher sensitivity for IgG RF in studies of Asian RA patients as compared to Caucasian and African-American studies. Conclusion: Increased frequency of IgG RF-positive in RA populations with different genetic background living in Malaysia argues for an environmental factor selectively amplifying the IgG RF response.