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Heterogenous nuclear RNP C1 and C2 core proteins are targets for an autoantibody found in the serum of a patient with systemic sclerosis and psoriatic arthritis.

OBJECTIVE
To determine a target recognized by anti-Bh autoantibody, found in the serum of a patient with the unusual coexistence of systemic sclerosis (SSc) and psoriatic arthritis (PsA).


METHODS
Antigens recognized by the anti-Bh serum were characterized by indirect immunofluorescence on HeLa cells, by conventional immunoblotting using nuclear extract or partially purified preparation of heterogenous nuclear RNP (hnRNP) proteins, and by 2-dimensional immunoblotting. For the analysis of cross-reactivity and immunofluorescence patterns, autoantibodies were affinity-purified by blot elution and then retested.


RESULTS
Comparison of the reactivity of the anti-Bh antibody with the monoclonal antibody 4F4 against both the hnRNP C proteins, together with the determination of biochemical properties of the autoantigens, led to the identification of C1 and C2 core proteins as the targets for the anti-Bh autoantibody.


CONCLUSION
Several essential components of the spliceosome are targeted by autoantibodies that are present in the sera of patients with systemic rheumatic diseases. We also found that the hnRNP core proteins C1 and C2 are recognized by the autoantibody present in the serum of a patient with SSc and PsA. C1 and C2 hnRNP proteins should be added to the several intracellular autoantigens recently shown to be cleaved by interleukin-1beta-converting enzyme-like enzymes during apoptosis.