Patients with rheumatoid arthritis (RA) from different ethnic groups present elevated levels of antibodies against Proteus mirabilis. This finding implicates P. mirabilis in the development of RA. The aim of this study was to investigate the importance of P. mirabilis in the etiopathogenesis of RA in Greek RA patients. In this study, 63 patients with RA and 38 healthy controls were included. Class-specific antibodies IgM, IgG, and IgA against three human cross-reactive and non-cross-reactive synthetic peptides from P. mirabilis-hemolysin (HpmB), urease C (UreC), and urease F (UreF)-were performed in all subjects, using the ELISA method. RA patients had elevated levels of IgM, IgG, and IgA antibodies against HpmB and UreC Proteus peptide which are significantly different compared to healthy controls: p = 0.005, p < 0.001, and p = 0.003 and p = 0.007, p = 0.002, and p < 0.001, correspondingly. Also, elevated levels of IgM, IgG, and IgA antibodies against the UreF Proteus peptide-which are non-cross-reactive with human tissue antigens-were observed and their significant difference compared to healthy controls (p = 0.007, p < 0.001, p < 0.001). Anti-peptide antibodies in RA patients showed a significant correlation with rheumatoid factors (Rf), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP), especially when patients were divided into subgroups according to the receiving treatment. Greek RA patients present elevated levels of antibodies against P. mirabilis antigenic epitopes, such as in North European populations, albeit Greek RA patients presenting the cross-reaction antigen in a low percentage. These results indicate that P. mirabilis through the molecular mimicry mechanism leads to inflammation and damage of the joints in RA.

Determination of the genetically controlled variants of the C3 system has been accomplished by electrophoresis on cellulose acetate membrane followed by immunofixation with a specific anti‐C3 antiserum. The results have been confirmed with the use of reference sera and compared with those obtained from conventional high voltage agarose gel electrophoresis. The interference of some electrophoretic variables on the technique has been investigated. The method is rapid, accurate, reliable and gives good separation of at least the three common C3 phenotypes.

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The distribution of phenotypes and gene frequencies of the group-specific component (Gc) and haptoglobin (Hp) were studied in 169 and 177 patients with multiple myeloma, respectively. The statistical analysis of our findings in comparison to the frequency of these genes in the general population does not support any correlation between the distribution of these phenotypes and the multiple myeloma or its immunological classes.

The Gm(1), Gm(2), Gm(4), Gm(12), and Inv(1) factors were studied in the sera of 56 patients suffering from rheumatoid arthritis and 26 from various rheumatic diseases, by the hemagglutination inhibition test, using optimally reacting mixtures of Ragg and Nagg sera. The distribution of these factors was found to agree with that of healthy Greeks. No correlation was found between hypergammaglobulinemia and the discovery of the Gm(1) and Inv(1) factors. The presence of the rheumatoid factor was independent of the Gm and Inv phenotypes.