The impact of protein modification on immunogenicity and arthritogenicity

Abstract

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease affecting about 1% of the Western world population. There are several theories regarding the etiopathogenesis.

The aim of this thesis was to study, using in vivo models, how inflammatory-associated modifications and pH-associated conformational changes of proteins influence their immunogenic and arthritogenic properties.

We chlorinated rat scrum albumin (RSA) and studied the effect of this modification upon immunization. We determined that chlorination breaks RSA tolerance regarding B cell immunity, demonstrated as high antibody (ab) titers to chlorinated RSA (RSA-Cl) in rats immunized with RSACl. Interestingly, such abs crossreacted with non-modified RSA.

In the second study we investigated the effect of chlorination on collagen II (CII). CII induces arthritis upon immunization in genetically susceptible animal strains, collagen-induced arthritis (CIA). To study the effect of chlorination we immunized rats with suboptimal doses of CII. We could observe an increased immunogenicity and arthritogenicity of chlorinated CII. Rats immunized with CII-Cl developed arthritis while rats immunized with CII did not. An antibody response to CII-Cl was detected in rats immunized with CII-Cl, and the abs crossreacted with CII. Rats immunized with CII-Cl demonstrated increased levels of IL-1beta and IFN-gamma mRNA compared to rats immunized with CII.

We conclude that chlorination is a protein modification that can break tolerance to an autoantigen. Our results also indicate that chlorinated CII has enhanced arthritogenicity.

pH-associated conformational modifications are of interest since pH at a site of inflammation is lower compared to in healthy tissue. Thus we investigated how pH-dependent changes of CII influence its arthritogenicity and immunogenicity. We demonstrated that CII at pH 7 has a fibrillar conformation and is more ellipsed compared to CII at acidic pH. Conformational differences are also reflected in the relative immunogenicity of the protein. CII at acidic pH induced arthritis in rats upon immunization while CII at neutral pH did not. In summary, this study demonstrates that conformational changes of a protein influence its structure and also its immunogenic properties.

In the fourth study we investigated the suppressive effect of MM in CIA. This substance had suppressive effect on arthritis development if given prophylactically. CDM was found to mainly suppress T-cell activation. CDM is thus a potential new anti-rheumatic drug.

The conclusion of this thesis is that inflammatory-mediated modifications of proteins influence their immunogenic properties. Such modifications can be of importance in the development of inflammatory autoimmune disease.