Extractable nuclear antigen (ENA) autoantibodies in SLE: an immunogenetic relationship with HLA, C4 and Bf alleles.

Sera from 36 subjects with systemic lupus erythematosus (SLE) were examined for extractable nuclear antigen (ENA) autoantibodies by immunoassay with the ribonucleoprotein (RNP) subset being determined by immunodiffusion. The prevalence of the genetic markers of HLA, the fourth complement component (C4) and properdin factor (Bf), which are all coded for within the major histocompatibility complex on chromosome 6 were analysed in relation to various parameters of these autoantibodies. The following associations were observed: The lowest ENA antibody titres of the RNP negative group were associated with HLA A9 (P less than 0.05), while the lowest RNA-ase sensitive ENA (RSE) subset antibody levels were associated with HLA Dr 1 (P less than 0.05). For the complement markers, C4 AQo was associated with the lowest affinity ENA antibodies (P less than 0.05), while the BF F allele and Fs phenotype had lower RSE antibody levels than did the S allele (P less than 0.05) and the SS phenotype (P less than 0.05) respectively. This study demonstrated diverse association between various MHC markers and ENA antibody parameters, indicating that there are distinctive immunogenetic influences over ENA autoantibodies in SLE.