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Ribosomal-P Antibodies

(September 2002)

(Download  Ribosomal_P Antibodies.pdf)

Systemic lupus erythematosus (SLE) is an autoimmune condition featuring inflammatory arthralgia, photosensitivity, and occasional internal organ involvement. SLE is characterised by the presence of antinuclear antibodies (ANA) in serum tested by indirect immunofluorescence.

ANA testing is highly sensitive (approximately 95%) for detecting SLE and related autoimmune conditions, but around 5% of patients with these disorders will display low-level or negative ANA results. The majority of these patients with 'ANA-negative lupus' are positive for antibodies to 'extractable nuclear antigens' (ENA), with SSA antibodies being particularly associated with photosensitivity. HAPS Immunology therefore recommends that SLE screening involve ANA plus ENA testing.

A significant proportion of patients with lupus (about 10%) are positive for antibodies to 'ribosomal-P' (Ribo-P). Antibodies to Ribo-P are directed against the three phosphoproteins (P0, P1, P2) located on the larger 60S subunit of the eukarytotic ribosomes, which share a common 22 amino acid C-terminal peptide epitope.

Testing for these antibodies in cases of suspected SLE is justified for two reasons:

  • While highly sensitive, ANA testing is poor in its specificity for lupus, with positive results seen in a range of inflammatory, infective and iatrogenic settings. Ribo-P antibodies, like antibodies to double-stranded DNA (dsDNA) and Sm antibodies are highly specific for lupus, assisting in clarifying the significance of positive ANA results.
  • Up to 5% of patients with lupus display only cytoplasmic (not nuclear) staining on ANA testing, and are hence reported as 'ANA-negative'. Many of these patients will display anti-Ribo-P antibodies.

Key Points

  • Screen for lupus and related conditions with ANA plus ENA.
  • Clarify positive ANA results with dsDNA and Ribo-P antibodies.
  • Check for Ribo-P antibodies where clinical suspicion of lupus persists in ANA-negative patients.

References

  1. Yasuma M, et al. Clinical Significance of IgG anti-ribosome P antibodies in patients with systemic lupus erythematosus. J Rheumatol 1990; 17:469
  2. Arnett F C, et al. Ribosomal P autoantibodies in systemic lupus erythematosus: Frequencies in different ethnic groups and clinical and immunogentic associations. Arthritis and Rheumatism 1996; 39:1833-1839
  3. Press J, et al. Antiribosomal P antibodies in pediatric patients with systemic lupus erythematosus and psychosis. Arthritis and Rheumatism 1996; 39: 671-676
  4. Isshi K and Hirohata S. Association of antiribosomal P protein antibodies with neuropsychotic systemic lupus erythematosus. Arthritis and Rheumatism 1996; 39: 1483-1490
  5. Elkon KB, et al. Identification and chemical synthesis of a ribosomal protein antigenic determinant in systemic lupus erythematosus. Proc Natl Acad Sci 1986; 83:7419-7423

About the Author

Dr Glenn Reeves, Immunology Staff Specialist, wrote this HAPS Communique. If you have any questions regarding this topic Dr Reeves can be contacted on: Telephone: (02) 49214000, Facsimile: (02) 49214400.

Immunology Contacts

Dr Glenn Reeves - Staff Specialist - 49214000
Professor Robert Clancy - Staff Specialist - 49236135
Immunology Laboratory - 49214000