A Single‐Stranded DNA‐Cross‐Reactive Immunogenic Epitope of Human Homocysteine‐Inducible Endoplasmic Reticulum Protein

Abstract

The mechanism involved in generating anti‐DNA antibodies (Abs) remains unclear, as DNA is poorly immunogenic. Molecular mimicry between DNA and non‐DNA substances has been implicated as a possible mechanism. We previously reported that homocysteine‐inducible endoplasmic reticulum protein (Herp), which is induced by endoplasmic reticulum stress, is recognized by anti‐double‐stranded DNA (dsDNA) IgG from patients with systemic lupus erythematosus and that immunization with Herp elicits anti‐dsDNA Abs in BALB/c mice. In this study, we observed that anti‐single‐stranded DNA (ssDNA) Abs were also generated in Herp‐immunized BALB/c mice and established an anti‐Herp monoclonal antibody (mAb), HT4, which specifically cross‐reacted with ssDNA. The epitope of the HT4 mAb on Herp, ‘EPAGSNR’, was identified by screening a synthetic peptide library. The binding of the HT4 mAb to the peptide was competitively inhibited by ssDNA. Immunization of the epitope peptide elicited anti‐ssDNA Abs in BALB/c mice. These results indicate that the epitope exists in a human self‐protein, mimics ssDNA and shows antigenicity for anti‐ssDNA Abs in normal mice. Anti‐ssDNA Abs are often found in patients with drug‐induced lupus erythematosus. Treatment with representative drugs that cause drug‐induced lupus (chlorpromazine, procainamide and hydralazine) induced Herp expression and apoptosis in HeLa cells. These findings suggest that molecular mimicry between Herp and ssDNA is involved in anti‐ssDNA Ab production in drug‐induced lupus.

Hypotheses of the origin of natural antibodies: A glycobiologist’s opinion

“…gangliosides cluster), not only different molecules of the same class (e.g. two polysaccharides), but also molecules from vari ous classes (protein + phospholipid) [88,89] (Fig. 3).…”

Plasma single-stranded DNA autoantibodies in the diagnosis of Hirschsprung’s disease

“…Single-stranded DNA (ssDNA) antibodies can bind nuclear DNA to induce apoptosis; thus, ssDNA antibodies are sensitive markers for programmed cell death and drug-induced apoptosis ( 19 , 20 ). ssDNA antibodies are specifically activated and amplified in the serum of patients with systemic lupus erythematosus (SLE), particularly drug-induced SLE ( 21 – 23 ). Therefore, ssDNA antibodies in serum can be used for the clinical diagnosis of drug-induced SLE.…”

Cell Death and Anti-DNA Antibodies

“…Immunization with Herp elicits production of not only anti-dsDNA antibodies but also antissDNA antibodies in BALB/c mice. Among several anti-Herp mAbs established in our laboratory, the HT4 anti-Herp mAb cross-reacts specifically with ssDNA [77]. The epitope of the HT4 mAb on Herp, EPAGSNR, was identified by screening a synthetic peptide library.…”