F. Bongiorni

The targets of nephritogenic antibodies in systemic autoimmune disorders

In situ formation of immune complexes is a well recognized mechanism of renal injury in systemic autoimmune disorders. The identification of intrinsic renal antigens that are targets of nephritogenic antibodies is a field of active investigation. Recently, two proteins expressed in the kidney have been characterized as renal antigens. Alpha-actinin, an actin-binding protein localized in glomerular podocytes, is the major target of nephritogenic anti-DNA antibodies. Alpha-enolase, a glycolytic enzyme, is a target of nephritogenic anti-DNA and non-anti-DNA antibodies.

Antibodies to inner ear antigens in Meniere's disease

Menieres disease (MD) is an idiopathic inner ear disorder characterized by fluctuating hearing loss, episodic vertigo and tinnitus. Its aetiology is unknown, although there is growing evidence that autoimmunity may be involved in its development. Using the Western blot immunoassay, we examined the reactivity to bovine inner ear antigens of sera from a series of MD patients who had previously been extensively studied for the presence of antibodies to collagens and membrane proteins. Reactivity to inner ear antigens of molecular weight 44 and 53 kD was found in 11/25 (44%) and 10/25 (40%) of the patients, respectively; both antigens were absent in the sera of healthy donors. It is still unclear whether the antibodies to 44 and 53 kD proteins play a role in the pathogenesis of MD or if they instead represent the result of inflammation and tissue destruction. Even if the latter is true, they may contribute to the perpetuation of the disease or play a role as a cofactor in association with other mechanisms.

Cell surface expression of activating receptors and co-receptors on peripheral blood NK cells in systemic autoimmune diseases

Objectives: A defined role for natural killer (NK) cells and their activating receptors in autoimmunity has not been clearly established. The aim of this study was to evaluate the levels of the CD3–CD56+ NK cells and their expression of receptors and co-receptors in the peripheral blood of patients with systemic autoimmune disorders. Methods: Thirty-four subjects with systemic sclerosis (SSc), 14 with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV), 14 with systemic lupus erythematosus (SLE), and 14 healthy donors were studied. The activating receptors NKp46, NKp44, NKp30, NKG2D, and DNAM-1 and the co-receptors NTB-A and 2B4 were analysed by flow cytometry on peripheral blood NK cells. Results: In SSc, AAV, and SLE we detected a significant decrease in the percentage of CD3–CD56+ NK cells compared to healthy controls. No differences in the expression of NKp46, NKp44, and NKp30 were identified. On the contrary, NKG2D and DNAM-1 expression was decreased in SLE, but not in SSc and AAV, NTB-A was decreased in SLE, and 2B4 in both SLE and SSc. No differences were detected between active and inactive SLE patients. In SSc, only patients affected by pulmonary arterial hypertension (PAH) and interstitial lung disease (ILD) had a low expression of DNAM-1, 2B4, and NKp30. Conclusions: These data demonstrate that patients with different systemic autoimmune diseases differ in the expression of activating receptors and co-receptors on CD3–CD56+ NK cells. The down-regulation of receptors and co-receptors in SSc with lung involvement suggests their possible role in this manifestation of the disease.

Heart- and skeletal muscle-specific antigens recognized by trichinellosis patient sera.

The heart can be seriously affected in human trichinellosis, and cardiac involvement can cause death. Experimental infections in rats have suggested the possible participation of immunopathological processes. The aim of the present paper was to investigate the possible presence in trichinellosis patient sera of antibodies recognizing host tissues and particularly the myocardium. Nineteen sera from late period trichinellosis patients, who acquired infection in the Poznan region (Poland), were tested by immunoblot on extracts from normal rat or human heart ventricle wall, spleen, placenta, kidney and skeletal muscle. Patients’ sera recognized several antigens that were not recognized by normal sera. On rat and human heart ventricle wall, a high proportion of sera (42%) reacted with a protein of 68 kDa (P < 0·05 compared to normal sera). The reactivity with this antigen, however, was not significantly different in patients with or without cardiac involvement. When sera were tested on skeletal muscle we found that 47% reacted with a protein of 27 kDa and 53% reacted with a protein of 41 kDa (P < 0·05 for both proteins, compared with normal sera). The reactivity against the 68 kDa antigen and against the 27 and 41 kDa skeletal muscle antigens was not observed on kidney, placenta and spleen extracts. Moreover, very few bands were observed on these tissues as compared to heart and skeletal muscle tissues, thus suggesting a high tissue specificity of the reactivity of trichinellosis sera. In conclusion, this study identifies organ‐specific autoantibodies in trichinellosis patient sera, their role in the pathogenesis of cardiac involvement being still unclear.

Structure and function of an autoantigen, alpha-enloase

The glycolytic enzyme 2-phosphoglyceratelyase (alpha-enolase) is an autoantigen in connective tissue disorders, and more frequently in patients with active renal disease. The enzyme has pleiotropic functions: it is also a structural protein, a stress protein induced by hypoxia and it acts as transcription factor in the nucleus. Alpha enolase is encoded by a single copy gene and only one mRNA species is detected. In order to define a structural basis for these different functions, we analyzed the isoelectric point of the enzyme. On a kidney extract fractionated by 2D electrophoresis, a mouse anti-enolase antiserum detects 5 spots of identical molecular weight but differing in pI. Some autoimmune sera react with all the spots, while other recognize only the acidic forms of alpha-enolase. We then analyzed the properties of the membrane form of enolase. Enolase is not a membrane structural protein, but it is strongly associated with the membrane, where it acts as plasminogen receptor. Anti-enolase antibodies purified from autoimmune sera react also with the membrane form of alpha-enolase: by flow cytometry, 7/9 antibody preparations bind in fact U937 cells, a human lymphomonocytoid cell line that expresses high density of plasminogen receptors. To investigate the possible functional role of membrane enolase, we evaluated the ability of monoclonal anti-enolase antibodies to induce cell damage or apoptosis. No monoclonal had a cytotoxic effect on U937 cells or was able to induce apoptosis in the same cell line. We then tested the ability of monoclonal anti-enolase antibodies to induce Ca2+ influx in U937 cells. One out of 4 monoclonal antibodies induced release of Ca2+ from intracellular stores. In conclusion, alpha-enolase exists as multiple isoforms, probably due to postranslational modifications, which seem to affect recognition by autoantibodies. It is presently unknown whether these modifications are tissue-specific and/or affect membrane expression of the enzyme. A possible link between Ca2+ influx and receptor functions of enolase is currently under investigation.