C4 allotypes in Thai systemic lupus erythematosus and rheumatoid arthritis patients

Abstract

The present study examined the pattern of C4 allotypes in 76 systemic lupus erythematosus (SLE), 34 rheumatoid arthritis (RA) and 100 healthy persons by immunoblotting electrophoresis and hemolytic function assay. Utilization of carboxypeptidase and neuraminidase treated EDTA-plasma resulting in better resolution of C4 alleles into single major bands has allowed clear distinction between C4 alleles. Assignment of C4 null allele was facilitated by the use of a laser densitometer and the evaluation of relative densities of C4A and C4B bands. The most common C4A and C4B allotypes in Thai were found to be C4A3 and C4B1 respectively which is in keeping with other findings. The frequency of C4A null allele (C4A*QO) in SLE patients (35.5%) are significantly increased in comparison with control subjects (14%, p=0.0015), with a relative risk of 3.38. There is a slight increase of C4B null allele (C4B*QA) in SLE patients (14.5% versus 7%, p=0.17). In the rheumatoid arthritis group, there is an increase of C4B 21 (8.8% versus 3%, p=0.17, R.R. =3.13) and C4B4 (2.9% versus 1%, p = 0.44, R.R. = 3.00) and significant decrease of C4 B2 (29.4% versus 53%, P = 0.029) in RA patients. The strong association of C4A*QO with Thai SLE patients in this study is consistent with others in different ethnic groups implicating the universal feature of this allotype in SLE. There is no distinct association of C4 allotypes with rheumatoid arthritis observed in this study. Further investigation on other major histocompatibility complex antigens particularly MHC II seems warranted.