Serological Markers in Rheumatoid Arthritis

Rheumatoid Arthritis Systemic autoimmune disease Characterized by chronic inflammation of the joints resulting in tissue degradation and joint destruction 1-2% of the world population Diagnosis – primarily on clinical manifestation, with only limited serological support

Clinical Manifestation of RA Morning stiffness Arthritis of 3 or more joint areas Arthritis of hand joints Symmetric arthritis Rheumatoid nodule Serum rheumatoid factor Radiographic change At least 4 of these criteria(1-4 at least for 6 wks)

Radiological Manifestations of RA Periarticular soft tissue swelling Osteoporosis Marginal erosions progressing to severe erosions of subchondral bone Synovial cyst formation and lack of bone repair Hand, feet, knee, hips, cervical spine, shoulder, elbow

Association of RA with HLA HLA-DR4, sometimes DR1associated with RA, but association is variable. Functional similarity : Shared epitope a.a. sequence in the HVR3 of the  chain (QK/RRAA at positions 70-74 of the HLA DRB1 chain)

Association of HLA with RA in Koreans Hong, et al. J Rheumatol 1996 DR4 61% vs 29% RR=3.7 Shared epitope 57% vs 22% RR=4.8 DRB1*0405 RR=9.4 DRB1*0401 RR=8.8 Kim, et al. Tissue Antigens 1999 DRB1*0405 RR=6.6 DQA1*03 RR=5.2 DQB1*04 RR=3.5 DQCAR113 RR=3.2 DQCAR115 RR=3.6 DQCAR 113/115 RR=11.2

Serological Markers in RA 1. RA factor (IgM) IgG/ IgA 2. Filaggrin associated Abs 1) antiperinuclear factor 2) antikeratin Ab 3) anticitrullinated filaggrin Ab 3. Anti-RA 33 4. Anti-Sa 5. pANCA 6. Other autoAb: HSP 60, type II collagen, calreticulin, calpastain, MTOC(?), GiM(?)

Rheumatoid Factors (RF) Ab to directed to the constant region of IgG Usually IgM type, but IgG, IgA Agglutination, nephelometry, ELISA based test Detected in 70-80% of RA, in high % in other autoimmune and infectious diseases, in up to 15% of healthy individuals

Anti-perinuclear Ab(1) Described by Nienhuis and Mandema, in1964 Ab to a component of a number of so-called keratohyaline granules surrounding the nucleus in IIF using buccal mucosa cells

Anti-perinuclear Ab(2) Profilaggrin, precursor of filaggrin colocalize with PF Keratohyalin granule of epidermis contains profilaggrin. Sensitivity 49-91%, specificity 73-99% APF positive buccal mucosa donor ~5% Correlated with bone erosion in short term

Anti-keratin Ab(1) Described by Young in 1979 Determined by IIF on cryosection of rat esophagus – stratum corneum of rat eosophagus epithelium High correlation with APF

Anti-keratin Ab(2) Not cytokeratin A neutral/acidic variant of human epidermis filaggrin, a terminal differentiation protein involeved in the aggregation of cytokeratin filament during cornification Sensitivity 36-59%, Specificity 88-99%

Anti-filaggrin Ab Filaggrin, cytokeratin filament aggregating protein – the target of the so called antikeratin antibodies (Simon et al., 1993, J Clin Invest) APF, AKA, anti-filaggrin extracted from human epidermis have similar diagnostic value… partially overlap, not totally identical (Vincent et al., 1999, Ann Rhem Dis)

Vincent, et al. Ann Rheum Dis 1999 Distribution fo RA and control serum samples with regard to AKA, AFA and APF positivity Vincent, et al. Ann Rheum Dis 1999 AFA immunoblot on filaggrin enriched epidermis extract

Filaggrin associated Ab Comparison of Serological Markers in RA RF Filaggrin associated Ab APF AKA(AFA) AFA Sensitivity (%) 70-80 40-80 35-55 Similar to APF/AKA Specificity 80-90 >90 Good Good ass /w prognosis Specific, Appear early, Less change of titer Stable Ag, ELISA or IB methods Bad Seronegative RF, Appear late, Titer fluctuation Less correl/w prognosis Lee available substrate, IF method IF method, Less sensitive than APF Less sensitive than APF

Anti-Citrullinated Filaggrin Ab RA associated Ab to filaggrin label the fibrous matrix of cornified cells but not the profillagrin containing keratohyalin granules in human epidermis (Simon et al., 1995, Clin Exp Immunol) RA specific autoAb recognize citrulline, posttranslational modified arginine residue (Simon et al., 1998, J Clin Invest)

Epidermis Cornification Profilaggrin: an acidic phosphorylated protein, Consisting of 10 –12 tandemly repeated filaggrin units separated by linker peptides Epidermis Dephophorylated Proteolytically cleaved Filaggrin: basic/neutral intermediate filament associated protein Citrullination by peptidyl arginine deaminase Cornification Arginine Citrulline Citrullinated Filaggrin

Simon et al., 1998, J Clin Invest

Simon et al., 1998, J Clin Invest

Anti-citrullinated Filaggrin Antibody on ELISA(MBL) 87 sera tested on Hallym University Medical Center Sensitivity 64%, Specificity 94%, Efficiency 76%

Specific presence of intracellular citrullinated proteins in rheumatoid arthritis synovium: Relevance to antifilaggrin autoantibodies Baeten et al., Arthritis Rheum 2001 Objectives: investigate the presence of citrullinated proteins in synovial membrane of RA Pt Methods: stain synovial tissue section of 88 RA pts and 52 other control pt with anti citrulline polyAbs(ACA) and affinity purified antifilaggrin autoantibody(AFA) Results: intracellularly staining of the lining and sublining layers of RA synovial tissue with ACA and AFA, which were colocalized

Prognostic factors in early RA Important clinical outcomes joint damage and functional disability Prognostic factors Joint involvement, RF positivity, ESR & CRP IgA RF, RF + AKA or AFA : more active Genetic predictors over RF : inconclusive Guideline for aggressive treatment

Juvenile RA Chronic inflammatory disease of unknown etiology and pathogenesis 1. Polyarticular onset JRA (=>5 joints) 30% 1) younger children RF(LA) negative 2) older girl RF(LA) positive 2. Pauciarticular onset JRA (1-4 joints) 50% 1) early onset, young girl /w iridocyclitis, positive ANA 2) late onset, boy /w HLA B27, ankylosing spondylitis 3. Systemic onset JRA ( fever, arthritis, skin rash, etc) 20%

Serological Markers for Juvenile RA(1) RF RF_LA 7-10% JRA, late onset polyarticular ELISA IgM RF 22-35% IgG RF 4-6% IgA RF 30-60% Hidden IgM RF not detected by conventional methods using IgM containing fraction from sephadex chromatography 65(systemic onset) – 85% (polyarticular)

Serological Markers for Juvenile RA(2) 2. ANA 50-70% positive in JRA young girl with pauciarticular onset, iridocyclitis 95-100% positive  ANA positivity well known risk factor for development of ant. uveitis Speckled and homogeneous No association with Sm, RNP, Ro, La, Scl70 Ab to Histone 40-70% of JRA

Serological Markers for Juvenile RA(3) 3. Other antibodies anticardiolipin antibody 7-42% anticollagen antibody 12-42% antiperinuclear factor non – 40%