p185, an immunodominant epitope, is an autoantigen mimotope.

An immunodominant peptide (p185(378-394)) derived from the c-erbB2 gene product, was recognized by an anti-DNA antibody, B3, and importantly by two classical DNA-binding proteins, Tgo polymerase and Pa-UDG. These reactivities were inhibited by DNA, confirming that the peptide mimicked DNA. BALB/c mice immunized with p185(378-394) developed significant titers of IgG anti-dsDNA antibodies. Screening of 39 human lupus sera revealed that 5% of these sera possessed reactivity toward p185(378-394). Representative mouse and human sera with anti-p185(378-394) reactivity bound intact p185, and this binding was inhibited by dsDNA. This is the first demonstration of a naturally occurring autoantigen mimotope. The present study identifies a potential antigenic stimulus that might trigger systemic lupus erythematosus in a subset of patients.

Beta-2-glycoprotein specificity of human anti-phospholipid antibody resides on the light chain: a novel mechanism for acquisition of cross-reactivity by an autoantibody.

We have recently shown that the anti-cardiolipin activity of human anti-phospholipid antibody UK4 (lambda) resides on its heavy chain. We now show that UK4 possesses strong reactivity to the plasma-protein beta2-Glycoprotein I (beta2-GPI) also. Utilizing chain shuffling experiments involving an unrelated anti-p185 antibody 4D5 (kappa) with no reactivity to beta2-GPI, we now demonstrate that both the constructs possessing the auto-antibody-derived light chain exhibited significant binding to beta2-GPI. However, the construct possessing UK4 heavy chain in association with 4D5 light chain, exhibited no anti-beta2-GPI activity. Furthermore, there was a low increase (approximately 10%) in the binding of UK4 to cardiolipin in the presence of beta2-GPI. The results demonstrate that anti-beta2-GPI activity resides on UK4 light chain and, importantly, this activity could be transferred to a novel antibody construct via the light chain alone. Computer-generated models of the three-dimensional structures of UK4 and its hybrids, suggest predominant interaction of UK4 light chain with domain IV of beta2-GPI. Molecular docking experiments highlight a number of potential sites on beta2-GPI for interaction of UK4 and indicate as to how beta2-GPI recognition may occur primarily via the autoantibody light chain. The study provides first demonstration of the occurrence of anti-phospholipid and anti-beta2-GPI activities separately on heavy and light chains of an autoantibody. The possible mechanisms that such antibodies may employ to recognise their antigens, are discussed.

Fine binding characteristics of human autoantibodies-partial molecular characterization.

The fine binding characteristics of three well-characterized human autoantibodies B3, RH14 (anti-DNA) and UK4 (anti-cardiolipin) in their IgG and cloned Fab formats, were investigated. Although in severe combined immunodeficiency (SCID) mice B3 and RH14 both induce proteinuria, only RH14 induces early features of lupus nephritis, whereas UK4 exhibits lupus anticoagulant activity. RH14 exhibited up to 10 fold higher binding to DNA compared to that shown by B3 or UK4 and involved significant electrostatic and phosphate group interactions. Only RH14 exhibited strong anti-Sm cross-reactivity residing on the C-terminus of the antigen as determined by the use of 76 overlapping 15mer peptides. Chain shuffling experiments indicate that anti-Sm/RNP and anti-Jo-1 activities of B3 and UK4 co-exist on one of the two chains (light, B3; heavy, UK4). The present study provides evidence that a human anti-DNA antibody can also be an anti-ENA antibody. Furthermore, the anti-DNA antibodies also exhibited cross-reactivity against glutathione-S-transferase and DNA polymerase PolIV of bacterial origin. This is the first demonstration of the presence of such cross-reactivities on lupus anti-DNA antibodies. We now demonstrate that subsets of sera from the patients with lupus, recognise these antigens. This observation may in some cases provide a mechanism for the common expression of a variety of autoantibodies observed in systemic lupus erythematosus (SLE).

Is alpha-actinin a target for pathogenic anti-DNA antibodies in lupus nephritis?

OBJECTIVE: Following recent reports that pathogenic murine anti-DNA antibodies bind to alpha-actinin, it was obviously of interest to assess the ability of human pathogenic anti-double-stranded DNA (anti-dsDNA) antibodies to bind this antigen. Both human monoclonal anti-DNA antibodies and antibodies affinity purified from the sera of patients with systemic lupus erythematosus (SLE) were investigated. METHODS: An enzyme-linked immunosorbent assay was established to measure immunoglobulin binding to alpha-actinin. Antibodies binding dsDNA were purified from the sera of SLE patients who either had active renal disease or had never had renal disease. Serum samples were selected at times when the patients' sera exhibited high IgG binding to dsDNA. The binding of supernatants from 3 high-affinity human anti-dsDNA IgG hybridomas (RH14, B3, and DIL-6) and 7 human IgM anti-DNA hybridomas was also investigated. RESULTS: A greater proportion of anti-dsDNA IgG-binding antibodies purified from patients with renal disease bound to alpha-actinin than did those purified from the sera of patients without renal disease. The specificity of binding to the 100-kd alpha-actinin molecule was confirmed by Western blotting. The pathogenic human antibodies RH14 and B3 bound strongly to alpha-actinin, while nonpathogenic DIL-6 bound very weakly. RT84, the IgM antibody that binds dsDNA with the highest affinity, exhibited the greatest binding to alpha-actinin. CONCLUSION: The results of our study support the findings of previous studies using murine anti-DNA monoclonal antibodies, which suggest that pathogenic anti-dsDNA antibodies cross-react with alpha-actinin.

Stroke following scorpion sting.

A 30 year old male presented with crossed buccofacial apraxia, apraxia for speech, Left UMN facial palsy and hemiplegia following scorpion sting. A cerebrovascular accident can develop following a scorpion sting due to venom-induced cerebral thrombosis.