Phage display identification of immunodominant epitopes and autoantibodies in autoimmune diseases

Phage display represents an invaluable tool to study autoimmune diseases. The side effects of immunosuppressive drugs for the treatment of autoimmune diseases raise awareness of the need to explore alternative therapeutic approaches such as antibodies and peptides. Therefore, phage display is an important technique for generating such molecules, so the purpose of this review is to determine the potential advantages of this technique in the research of autoimmune diseases. Many studies have also demonstrated the efficacy of phage display in identifying immunodominant epitopes of autoimmune diseases such as Goodpasture disease, immunologic thrombocytopenia, and systemic lupus erythematosus. Phage display peptide libraries have been screened with immunopurified autoantibodies from patients with autoimmune diseases. This makes it possible to more precisely locate the autoantibody binding sites, reveal a possible epitope sharing between the host and microbe, and identify a motif that mimics an antigenic structure such as that of dsDNA. Several studies have been conducted that have investigated the effectiveness of phage display in isolating autoantibody repertoires of autoantibodies against human epitopes. This allows the identification and design of antibody fragments (e.g., Fab, scFv, sdAb) that could block the binding of autoantibodies such as the deposition of IgG in the kidney and reduce the clinical signs of disease. In conclusion, phage display helps identify common epitopes and hotspot residues that can be potential therapeutic targets for the treatment of autoimmune diseases. This leads to a better understanding of the immunopathogenesis of autoimmune diseases and the development of more specific therapeutic strategies.

Two HLA-B14 Subtypes (B*1402 and B*1403) Differentially Associated with Ankylosing Spondylitis Differ Substantially in Peptide Specificity but Have Limited Peptide and T-cell Epitope Sharing with HLA-B27

The peptide specificity of HLA-B*1403, an allotype associated with ankylosing spondylitis (Lopez-Larrea, C., Mijiyawa, M., Gonzalez, S., Fernandez-Morera, J. L., Blanco-Gelaz, M. A., Martinez-Borra, J., and Lopez-Vazquez, A. (2002) Arthritis Rheum. 46, 2968–2971) was compared with those of the non-associated B*1402 and the prototypic disease-associated B*2705 allotypes. Although differing by a single residue (L156R), B*1402 and B*1403 shared only 32–35% of their peptide repertoires. Subtype-related differences observed in multiple peptide positions, including P3 and P7, were largely explained by a direct effect of the L156R change on peptide specificity. The HLA-B14 subtypes shared only ∼3% of their peptide repertoires with B*2705. This was due to distinct residue usage at most positions, as revealed by statistical comparison of B*1402, B*1403, and B*2705-bound nonamers. Nevertheless, shared ligands between B*2705 and B*1403 were formally identified, although ligands common to B*2705 and B*1403, but absent from B*1402, were not found. Alloreactive T-cells were used as a tool to analyze epitope sharing among B*1402, B*1403, and B*2705. The percentage of cross-reactive T-cell clones closely paralleled peptide overlap, suggesting that shared ligands tend to maintain their antigenic features when bound to the different allotypes. Our results indicate that B*1403 and B*2705 can present common peptides. However, both the disparity of their peptide repertoires and the lack of binding features shared by these two allotypes, but not B*1402, argue against, although do not exclude, a mechanism of spondyloarthritis mediated by specific ligands of B*2705 and B*1403.

1,25-Dihydroxy Vitamin D3 and Tri-iodothyronine Stimulate the Expression of a Protein Immunologically Related to Osteocalcin

Osteocalcin (OC), a bone-specific protein, is a marker of late osteoblastic differentiation. Its expression is influenced by various growth factors and hormones. We investigated the effect of 1,25-dihydroxy vitamin D3 (D3) and tri-iodothyronine (T3) on OC expression in osteoblast-like MC3T3-E1 cells. A heterologous OC green fluorescence protein (GFP) fusion vector was established and expressed to study possible effects on protein transport. Immunostaining of endogenous OC revealed a significant increase in the percentage of positive cells after D3 and T3 treatment. This was consistent for MC3T3-E1 cells as well as nonosteogenic NIH-3T3 and mammary carcinoma cells, but not for neuroblastoma cells. The perinuclear immunostaining corresponded to the NBD C6 ceramide Golgi staining. Conversely, we found a strong induction of OC in MC3T3-E1 cells at the mRNA and protein levels only with T3 and not with D3. OC mRNA and protein expression was not detected in NIH fibroblasts. OC GFP transfection experiments indicate rapid transport and secretion of OC, because OC GFP was not found to be accumulated at intracellular compartments after hormone treatment. We conclude that the strong perinuclear immunostaining does not represent OC but a protein immunologically related to OC, as indicated by preabsorption experiments. The expression of this OC epitope-sharing protein is regulated by both D3 and T3 in the osteoblastic MC3T3-E1 and in nonosteogenic cells.