Anti-ribosomal P antibodies as a single serological marker in SLE: lupusin disguise

J Kleinnijenhuis1, RG van der Molen2, PML Franssen3, JH Berden3, JW van der Meer1, JFM Jacobs2

Departments of 1Medicine, 2Laboratory of Medicine, and 3Nephrology, Radboud University Medical Centre, Nijmegen, The Netherlands

Systemic lupus erythematosus (SLE) is a chronic, multi-faceted autoimmune disease that is characterized by thepresence of autoantibodies predominantly directedagainst nuclear proteins and nucleic acids (1).Surprisingly, the most specific SLE autoantibody cur-rently known is not directed against a nuclear antigenbut against cytoplasmic ribosomal P (anti-P) (2). So far,anti-P has always been reported in the presence of one ormore other SLE-associated autoantibodies. Here wereport a patient with massive polyarthritis and lupusnephritis with anti-P as the single serological marker(3, 4). As anti-P is included in neither the classificationcriteria of the American College of Rheumatology(ACR) (5) nor the newly developed Systemic LupusInternational Collaborating Clinics (SLICC) classifica-tion criteria for SLE (6), there is a risk that the diagnosisof SLE in similar patients is not made or is delayed. Ourfinding of anti-P as the single serological marker for SLEagainst the background of the high specificity of anti-P forSLE should kindle a discussion on the inclusion of anti-Pin the classification criteria.A 44-year-old Caucasian man presented with diffuse

myalgia and fatigue since 2 years. In the past 9 months hehad lost 15 kg bodyweight and he complained of severepolyarthralgia, for which he needed fentanyl patches. Hehad smoked cigarettes for 30 pack-years. Physical exami-nation revealed that he had low blood pressure (BP 98/50

mmHg), overt polyarthritis affecting more than 30 joints,and massive oedema. Further examination was normal,and there were no skin lesions.

Laboratory results were C-reactive protein (CRP) 131mg/L, albumin 12 g/L, and microscopic haematuria withcellular casts and proteinuria (1.05 g/24 h). Serology forautoimmune diseases did not show any anti-nuclear anti-bodies (ANA), but there was clear cytoplasmic staining(Figure 1A). The screening for antibodies against extrac-table nuclear antigens (ENAs), DNA, and nucleosomeswas negative and complement was normal. Anti-phospholipid antibodies were negative as determined bythe lupus anticoagulant test, as were anti-cardiolipin anti-bodies and anti-β2-glycoprotein antibodies. The directCoombs’ test showed a titre of 1:2, which was interpretedas negative; other parameters [lactate dehydrogenase(LDH) haptoglobin] were not compatible with haemoly-sis. The cytoplasmic fluorescence seen in the ANA test,together with the clinical picture, prompted us toperformmore extensive investigations for autoantibodies.Strong anti-P reactivity was detected in the EurolineANA-profile 1 (Euroimmun, Luebeck, Germany), whichwas confirmed with high concentrations of anti-P on anImmunocap analyser (23 000 U/mL; Phadia, Freiburg,Germany). A renal biopsy showed focal segmental necro-tizing glomerulonephritis with extensive immune depos-its and was classified as focal proliferative lupus nephritis

A B (i) B (ii)

Figure 1. (A) Immunofluorescence staining of HEp-2000 cells. Fine speckled cytoplasmic staining pattern (titre 1:1280). (B) Histological analysis ofsilver-stained renal biopsy. (i) Approximately 20% of the glomeruli had active focal proliferative lesions and (ii) 15% of the glomeruli had chronic lesionswith glomerular scars. Extensive immune deposits of IgG, IgA, IgM, C1q, and C3 (so-called ‘full house’) could be visualized by immunofluorescencemicroscopy (data not shown). Conclusion: focal proliferative and sclerosing lupus nephritis ISN/RPS Class III (A/C).

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ISN/RPS Class III A/C (Figure 1B). Based on the com-bined clinical, serological, and pathological data, thepatient was diagnosed with SLE, although the patientfulfilled only two (arthritis and renal disorder) of theACR criteria (5).Treatment with high-dose corticosteroids and myco-

phenolate mofetil resulted in a rapid improvement ingeneral well-being and polyarthritis, with immediatedecrease of CRP and anti-P levels. The ANA remainednegative during the 1-year follow-up.The reported prevalence of anti-P in SLE patients

ranges from 6% to 46% and is highest in Asian patients(3, 7). It is known from the literature that anti-P can bepresent in ANA-negative SLE patients (8) and that anti-Pcan be the only persisting autoantibody after treatment(9). However, as far as we know, this is the first reportedSLE patient to present with anti-P as the single serologicalautoantibody marker. This novel finding has severalimportant clinical consequences.First, our case report demonstrates that there is a risk

that the diagnosis of SLE is not made or is delayed in apatient with anti-P as the single autoantibody markerbecause of a negative ANA test and a negative ENAscreen, as anti-P is not included in most conventionalENA-screening assays (10). In addition, in the newlydeveloped SLICC classification criteria for SLE, anti-Pis not included (6). The SLICC criteria stress the clinicalimportance of nephritis in SLE and define ‘a biopsy-proven nephritis compatible with SLE in the presence ofANAs or anti-dsDNA’ as a stand-alone clinical criterionfor SLE. Of note, our patient, with a biopsy-provennephritis, does not strictly fulfill this criterion becauseanti-P is an anti-cytoplasmic and not an anti-nuclearantibody. Anti-P has been recognized since 1985 andis appreciated as an additional biomarker that is almostexclusively present in patients with SLE (specificity>98%) (2, 3). On average, anti-P-positive patients pro-duce three to four additional autoantibody specificities(mainly anti-dsDNA and anti-Sm), and as a result theANA test in these patients is usually positive, even thoughribosomal-P is a cytoplasmic autoantigen (4). The cyto-plasmic fluorescence observed and reported in the ANAassay was a strong trigger for in-depth autoantibody ana-lysis. It clearly stresses the importance of the positionstatement of the ACR written in 2009, indicating thatthe immunofluorescence ANA assay is the gold standardfor ANA testing (11).Second, an association between anti-P and certain

clinical SLE manifestations such as nephritis, malarrash, arthritis, hepatic involvement, and neuropsychiatric

symptoms has been documented, but always in the pre-sence of other autoantibodies (3, 4). Here we demonstratea patient with extensive polyarthritis and lupus nephritiswith anti-P as the single marker.

Finally, this previously unrecognized serologicalprofile in which an SLE patient presents with anti-Pas the single autoantibody marker should kindle adiscussion on inclusion of anti-P in the classificationcriteria.

Acknowledgements

We thank EJ Steenbergen for histological analysis of the renal biopsy.

References1. Rahman A, Isenberg DA. Systemic lupus erythematosus. N Engl J

Med 2008;358:929–39.2. Elkon KB, Parnassa AP, Foster CL. Lupus autoantibodies target

ribosomal P proteins. J Exp Med 1985;162:459–71.3. Haddouk S, Marzouk S, Jallouli M, Fourati H, Frigui M, Hmida YB,

et al. Clinical and diagnostic value of ribosomal P autoantibodies insystemic lupus erythematosus.Rheumatology (Oxford) 2009;48:953–7.

4. Heinlen LD, Ritterhouse LL, McClain MT, Keith MP, Neas BR,Harley JB, et al. Ribosomal P autoantibodies are present before SLEonset and are directed against non-C-terminal peptides. J Mol Med(Berl) 2010;88:719–27.

5. Tan EM, Cohen AS, Fries JF, Masi AT, Abe K, Sakuma H, et al.The 1982 revised criteria for the classification of systemic lupuserythematosus. Arthritis Rheum 1982;25:1271–7.

6. Petri M, Orbai AM, Alarcon GS, Gordon C, Merrill JT, Fortin PR,et al. Derivation and validation of the Systemic Lupus InternationalCollaborating Clinics classification criteria for systemic lupuserythematosus. Arthritis Rheum 2012;64:2677–86.

7. Hanly JG, Urowitz MB, Su L, Bae SC, Gordon C, Clarke A, et al.Autoantibodies as biomarkers for the prediction of neuropsychiatricevents in systemic lupus erythematosus. Ann Rheum Dis2011;70:1726–32.

8. Sugisaki K, Takeda I, Kanno T, Nogai S, Abe K, Sakuma H, et al.An anti-nuclear antibody-negative patient with systemic lupuserythematosus (SLE) accompanied with anti-ribosomal P antibody(anti-P). Intern Med 2002;41:1047–51.

9. Martin AL, Reichlin M. Fluctuations of antibody to ribosomal Pproteins correlate with appearance and remission of nephritis inSLE. Lupus 1996;5:22–9.

10. Damoiseaux JG, Tervaert JW. FromANA to ENA: how to proceed?Autoimmun Rev 2006;5:10–17.

11. Meroni PL, Schur PH. ANA screening: an old test with newrecommendations. Ann Rheum Dis 2010;69:1420–2.

Joannes FM Jacobs, Department of Laboratory Medicine, LaboratoryMedical Immunology, Radboud University Nijmegen Medical Centre,Geert Grooteplein 10, 6525 GA Nijmegen, The Netherlands.E-mail: H.Jacobs@labgk.umcn.nl

Accepted 28 November 2013

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