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.

A family based study shows no association between rheumatoid arthritis and the PADI4 gene in a white French population

BACKGROUND

Autoantibodies to citrullinated proteins (ACPA) are considered a specific marker for rheumatoid arthritis. Peptidylarginine deiminase (PAD) is the enzyme that converts arginyl into citrullyl residues; different isoforms of the enzyme are expressed in mammals. It has been suggested that the PADI4 gene may contribute to genetic susceptibility to rheumatoid arthritis, but conflicting results have been obtained in different populations.

OBJECTIVE

To test the hypothesis that the PADI4 gene may confer susceptibility to rheumatoid arthritis in a white French population, using powerful and highly reliable family based association tests.

METHODS

DNA samples were analysed from 100 families where one member was affected by rheumatoid arthritis and both parents were available for sampling. Five single nucleotide polymorphisms, located within the PADI4 gene and in its close proximity, were genotyped by restriction fragment length polymorphism, and haplotypes were constructed. The analysis involved use of the transmission disequilibrium test and genotype relative risk. ACPA were detected by ELISA on cyclic citrullinated peptides and on human deiminated fibrinogen.

RESULTS

No single SNP or haplotype was associated with the disease, or was preferentially transmitted. No association was found when patients were partitioned according to ACPA positivity.

CONCLUSIONS

No PADI4 haplotype is associated with rheumatoid arthritis in a white French population. The role of genes encoding the other PAD isoforms, or modulating tissue expression or enzyme activity, remains to be elucidated.

Antibodies to inner ear antigens in Meniere's disease

Meniere's 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.

Use of human chondrocyte cell cultures to identify and characterize reactive antibodies in rheumatoid arthritis sera

OBJECTIVE

To study the reactivity of rheumatoid arthritis (RA) sera with human chondrocyte populations isolated from normal cartilage and expanded in vitro.

METHODS

Human articular chondrocytes were cultured as adherent (non-differentiated) cells on plastic dishes or in suspension (differentiated) on dishes previously coated with a thin layer of 1% agarose. Sera from 28 RA patients and 5 paired synovial fluids were tested on lysates from chondrocytes and fibroblasts as control by immunoblot. Antigen expression on the cell membrane was evaluated by flow cytometry in a few sera.

RESULTS

In 9/28 RA sera IgG antibodies specific for chondrocyte antigens (97 kDa, 74 kDa, 67 kDa, 60 kDa, 54 kDa, 48 kDa and 37 kDa) were detected. Twelve sera reacted with proteins expressed both on chondrocytes and fibroblasts and 7 with fibroblasts only; two sera had no reactivity. When lysates from adherent or suspension chondrocytes were compared, RA sera reacted with higher intensity and detected more antigens on chondrocytes cultured in suspension. Flow cytometry assay demonstrated that RA sera are able to recognize antigens expressed on the cell membrane of the human chondrocytes.

CONCLUSION

Our data indicate that: a) 32% of the RA sera contain antibodies reactive with antigens expressed exclusively by chondrocytes, but this value rises to 75% if antigens expressed both by chondrocytes and fibroblasts are considered; b) the reactivity of fully differentiated chondrocytes in suspension culture is higher than the reactivity of chondrocytes cultured in monolayer; and c) some of the chondrocyte-specific antigens identified are associated with the chondrocyte membrane. Thus, in vitro cultured chondrocytes may be used to study both the specificity and the biological activity of autoantibodies in RA.

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.