Autoimmune sera recognize a 100 kD nuclear protein antigen (sp-100)

Area of Science:

• Immunology
• Cell Biology
• Autoimmunity

Background:

• Autoimmune diseases often present with autoantibodies targeting nuclear components.
• Distinctive antinuclear antibody (ANA) patterns aid in diagnosing specific autoimmune conditions.
• Undifferentiated connective tissue diseases (UCTD) and Sjögren's syndrome (SS) can exhibit unique serological markers.

Purpose of the Study:

• To characterize a novel nuclear spot immunofluorescence pattern observed in patients with autoimmune disorders.
• To identify the specific autoantigen targeted by antibodies producing this distinct nuclear pattern.
• To establish the diagnostic utility of this pattern and its corresponding antigen.

Main Methods:

• Immunofluorescence studies using HEp-2 cells to detect antinuclear antibodies (ANAs).
• Immunoblotting assays with HeLa nuclear protein fractions to identify the target antigen.
• Affinity purification of specific autoantibodies for confirmation.

Main Results:

• A unique nuclear spot pattern, excluding nucleoli, was observed in sera from patients with UCTD, SS, and primary biliary cirrhosis (PBC).
• This pattern was distinguishable from established ANA patterns like anti-centromere and anti-Scl-70.
• Immunoblotting identified a 100 kD polypeptide with a pI of approximately 5.2 as the common antigenic target (designated SP-100).
• Affinity purification confirmed the specificity of autoantibodies for the SP-100 antigen.

Conclusions:

• The distinct nuclear spot pattern is associated with antibodies against a 100 kD nuclear protein (SP-100).
• This finding provides a new serological marker for certain autoimmune diseases.
• The SP-100 antigen represents a potential diagnostic target in autoimmune research.