Mutant mouse lysozyme carrying a minimal T cell epitope of hen egg lysozyme evokes high autoantibody response

[Modulation of Aggregation and Immunogenicity of a Protein: Based on the Study of Hen Lysozyme]

This study focuses on the modulation of protein aggregation and immunogenicity. As a starting point for investigating long-range interactions within a non-native protein, the effects of perturbing denatured protein states on their aggregation, including the formation of amyloid fibrils, were evaluated. The effects of adducts, sugar modifications, and stabilization on protein aggregation were then examined. We also investigated how protein immunogenicity was affected by enhancing protein conformational stability and other factors.

Transfusion-induced autoantibodies and differential immunogenicity of blood group antigens: a novel hypothesis

Blood bank serology has identified hundreds of red blood cell (RBC) antigens contained within numerous blood group systems. Although most blood group antigens are defined by amino acid polymorphisms in the extracellular domain of membrane proteins, it is also possible that additional nonexofacial polymorphisms (NEPs) may exist within cytoplasmic or transmembrane domains. To assess this possibility, we analyzed several blood group molecules by searching the SNPper database for nonsynonymous single-nucleotide polymorphisms. We report the identification of a number of NEPs in the Kell, Kidd, and Duffy molecules. Because the identified NEPs are not exposed on the surface of intact RBCs and are, thus, not accessible to recipient antibodies, they would neither be detected by blood bank serology in vitro, nor would they be recognized targets in hemolytic transfusion reactions in vivo. The presentation of peptides containing NEPs by recipient MHC Class II molecules, however, would nevertheless produce helper T-cell epitopes. In addition to identifying NEPs in human blood group molecules, we explore a novel hypothesis that the presence of NEPs contributes to the immunogenicity of blood group antigens. We further hypothesize that NEPs provide a mechanism by which transfusion can lead to anti-RBC autoantibodies, which are known to occur in humans after transfusion. The scientific basis, existing evidence, approaches to testing, and predicted biology of this hypothesis are presented.

Crystal Structure of Tapes japonica Lysozyme with Substrate Analogue

Tapes japonica lysozyme (TJL) is classified as a member of the recently established i-type lysozyme family. In this study, we solved the crystal structure of TJL complexed with a trimer of N-acetylglucosamine to 1.6A resolution. Based on structure and mutation analyses, we demonstrated that Glu-18 and Asp-30 are the catalytic residues of TJL. Furthermore, the present findings suggest that the catalytic mechanism of TJL is a retaining mechanism that proceeds through a covalent sugar-enzyme intermediate. On the other hand, the quaternary structure in the crystal revealed a dimer formed by the electrostatic interactions of catalytic residues (Glu-18 and Asp-30) in one molecule with the positive residues at the C terminus in helix 6 of the other molecule. Gel chromatography analysis revealed that the TJL dimer remained intact under low salt conditions but that it dissociated to TJL monomers under high salt conditions. With increasing salt concentrations, the chitinase activity of TJL dramatically increased. Therefore, this study provides novel evidence that the lysozyme activity of TJL is modulated by its quaternary structure.

Low HEMA conjugation induces high autoantibody titer in mice

2-hydroxyethylmethacrylate (HEMA) is a known causal agent of hypersensitivity to resin composites. We have reported that immunization with HEMA conjugated to mouse serum albumin (MSA) induces an autoantibody response in mice. In this study, we investigated both the activity and the avidity of autoantibodies induced by immunization with various HEMA conjugations to MSA. Female Balb/c mice were given MSA carrying 3, 7, 15, or 22 HEMA molecules. Antigen-specific IgG and IgE antibodies were determined by ELISA, and average antibody avidity by thiocyanate dissociation. Immunization with MSA carrying the lowest number of HEMA molecules induced a significantly higher IgG and IgE anti-MSA autoantibody response, with significantly higher IgG antibody avidity, than did the more heavily conjugated preparations. The results suggest that the lower the degree of HEMA conjugation to self-protein, the higher the risk for autoantibody production to the carrier protein. These findings suggest a mechanism of potential relevance in humans.

Lack of patent liver autoimmunity after breakage of tolerance in a mouse model

We report in this work that a cellular and humoral autoreactive response can be induced against liver-specific self-determinants by repeated immunization with a chimeric tissue-specific self-antigen carrying a heterologous T(h) epitope. Epitope spreading rendering the autoimmune reaction independent of the presence of the cognate heterologous help is also demonstrated. Although neutrophil infiltrates can be demonstrated in the livers of treated mice, no clinical sign of organ damage is observed. These findings suggest that breakage of tolerance by this means leads the process only up to the next checkpoint in the progression of autoimmune disease and that further events are required to precipitate functional organ impairment.

[Enjoying research on lysozymes for 42 years]

I have pursued research on lysozymes for 42 years. During that time, I made Several new findings, some of them by chance. My enjoyment of the following areas is reviewed: the story of tryptophan; protease digestion mechanisms; peptide mapping with RP-HPLC; gene engineering; renaturation of protein; catalytic residues; fluctuation and function; stabilization; folding; antigenecity; tolerance; and various lysozymes.

B-cell repertoire specific for an unfolded self-determinant of mouse lysozyme escape tolerance and dominantly participate in the autoantibody response

We previously found that autoantibodies against mouse lysozyme (ML) were strongly induced in normal BALB/c mice when immunized with mutant ML that has triple mutations rendering the dominant T-cell epitope of hen egg lysozyme (HEL), HEL 107-116. As T cells specific for HEL 107-116 were primed in these mice, the anti-ML immunoglobulin G (IgG) responses would be the result of collaborations between autoreactive B cells specific for ML and T cells specific for HEL 107-116. Serum IgG responses against ML were dominantly focused on the ML 14-69 region, indicating that B cells responding to the epitope escape tolerance. In the present study, we prepared several monoclonal antibodies (mAbs) specific for ML 14-69 and examined their antigen specificities in detail, to characterize the nature of the remaining B-cell repertoire specific for ML. mAbs specific for ML 14-69 interacted weakly with soluble, native ML, but the interactions were strengthened by denaturation of ML. The apparent affinity constants between these mAbs and ML showed an increase, ranging from six- to 80-fold, by denaturation of ML. Therefore, these mAbs were more specific for the denatured determinant than for the determinant in the native structure. These results indicate that a substantial number of autoreactive B cells, specific for the unfolded conformation of ML, escape tolerance and are dominantly involved in the autoantibody response to ML. Our finding provides important information to understand the naturally occurring autoreactive B-cell repertoire in normal mice.

[Foundation of the bases for protein research and its application to the pharmaceutical science field]

This paper reviews the results of basic research conducted by the author's group to determine appropriate methods to develop protein-based drugs. These include production strategies, elucidation of physiologic function, improving existing pharmaceuticals, de novo design, and protein reconstruction. The antigenicity of modified proteins and methods to induce antigenic protein tolerance are also described.

Enhanced immunogenicity of a functional enzyme by T cell epitope modification

BACKGROUND

T helper epitopes are necessary for the induction of high titers of antigen-specific IgG antibodies. We are interested in the epitope modification of intact proteins as a method to enhance their immunogenicity for the generation of recombinant protein-based vaccines.

RESULTS

Hartley strain guinea pig T cell epitopes were mapped for two related bacterial proteases. Two T cell epitopes were found in one of the proteases, while a comparatively reduced immunogenicity protease had no detectable T cell epitopes. A T cell epitope sequence homologous to the immunogenic protease was created in the less immunogenic protease by changing a single amino acid. Proliferative responses to the whole protein parent enzyme were two-fold higher in splenocyte cultures from variant-immunized animals. We found that the single amino acid change in the variant resulted in a protein immunogen that induced higher titers of antigen-specific IgG antibody at low doses and at early time points during the immunization protocol. The serum from parent- and variant-immunized guinea pigs cross-reacted at both the protein and the peptide level. Finally, animals primed to the variant but boosted with the parent enzyme had higher levels of antigen-specific IgG than animals immunized with the parent enzyme alone.

CONCLUSIONS

With a single amino acid change we have introduced a T cell epitope into a comparatively low-immunogenic enzyme and have increased its immunogenicity while retaining the enzyme's original proteolytic function. The ability to immunomodulate proteins while leaving their function intact has important implication for the development of recombinant vaccines and protein-based therapeutics.

A single amino acid substitution in a self protein is sufficient to trigger autoantibody response

We determined if a single amino acid substitution in a self protein causes autoantibody responses. Mouse lysozyme (ML) was used as a model self protein, and a mutant ML (F57L ML) was prepared by replacing 57Phe of ML to Leu, an approach which resulted in introducing into ML the immunogenic sequence of peptide 50-61 of hen egg lysozyme (HEL) restricted to I-A(k) MHC class II molecule. We found that F57L ML but not native ML primed HEL specific T cells and triggered ML specific autoantibody responses in B10.A and C3H mice (I-A(k), I-E(k)). Peptide regions, ML 14-69 and ML 98-130, were major epitopes of autoantibodies in both strains of mice. These findings indicate that a single amino acid substitution in self proteins can cause an autoantibody response when the mutated region is presented by MHC class II molecules and recognized by T cells.