Elevated Membrane and Soluble CD64: A Novel Marker Reflecting Altered FcγR Function and Disease in Early Rheumatoid Arthritis That Can Be Regulated by Anti-Rheumatic Treatment

<div><p>Objectives</p><p>Fc receptors (FcR) interacting with immune complexes (ICs) is a central event in the immune pathogenesis of rheumatoid arthritis (RA). Here we asked if a specific FcR is linked to RA pathogenesis and if FcR activities relate to disease and treatment outcome in early RA.</p><p>Material and Methods</p><p>Twenty autoantibody-positive RA patients and 33 HC were included. The patients were evaluated before and after treatment with methotrexate and prednisolone. At follow-up, the EULAR response criteria were applied to determine the individual treatment outcomes. Serum immunoglobulin levels were measured and the expression of FcR for IgG (FcγR) and IgA (FcαR) on peripheral blood monocytes were determined by flow cytometry. The monocytic FcγR function was evaluated by human IgG1 and IgG3 IC-binding and TNFα stimulated release. Plasma levels of soluble FcRs (sFcRs) were determined with ELISA.</p><p>Results</p><p>The IgG1 and IgG3 levels were elevated in the RA sera. The RA monocytes expressed more CD64 and cell surface-bound IgG than HC monocytes, and showed an impaired FcγR function as reflected by changes in IC-binding and decreased IC-stimulated TNFα secretion. These findings correlated significantly with different disease activity markers. Furthermore, sFcRs were elevated in the patient plasma, and sCD64 was specific for RA (compared with a reference group of patients with active psoriatic arthritis). Following treatment, immunoglobulins and sFcR levels were reduced, whereas membrane CD64 was only decreased in patients with good response to treatment.</p><p>Conclusions</p><p>Early RA patients display increased membrane and soluble CD64 and an impaired FcγR function correlating with joint disease activity. Beneficial responses of anti-rheumatic treatment in patients reduce CD64. These data suggest sCD64 as an important objective biomarker in RA.</p></div

Reduction of CD64 expression after anti-rheumatic treatment in good responders.

<p>The monocyte expressions of CD64 (A), IgG bound CD64+ cells (B), CD16 (C) and CD89 (D) before and after treatment with methotrexate and prednisolone in early RA patients, defined as good responders (<i>n</i> = 7) or non responders (<i>n</i> = 8). (FV = first visit, FU = follow up, MFI = mean fluorescent intensity).</p

Fcγ receptor expression and function reflecting severity of joint inflammation in drug naïve early RA patients (<i>n</i> = 20).

<p>Abbreviations; MFI = mean fluorescence intensity, MS = morning stiffness, VAS = visual analogue scale, DAS = disease activity score, CRP = C-reactive protein, IC = immune complex, TJC = tender joint count, SJC = swollen joint count, TNFα = tumor necrosis factor alpha, PG = patient global assessment of disease activity, E-SR = sedimentation rate, HAQ = health assessment questionnaire, r / p = regression coefficient / p-value.</p><p>Fcγ receptor expression and function reflecting severity of joint inflammation in drug naïve early RA patients (<i>n</i> = 20).</p

Characteristics of healthy controls and early RA patients.

<p>Ranges are presented in brackets. DAS28 = disease activity score (28 joint index), HAQ = health assessment questionnaire, E-SR = sedimentation rate, CRP = C-reactive protein, RF = rheumatoid factor, ACPA = anti–citrullinated protein antibody, n.a. = not applicable, n.d. = not done.</p><p>Characteristics of healthy controls and early RA patients.</p

Characteristics of good and non responders in early RA.

<p>CRP-concentrations (A), the activating:inhibiting FcR expression ratio (B), and the monocyte CD32b expression (C) in good (<i>n</i> = 7) versus non responders (<i>n</i> = 8) before and after treatment with methotrexate and prednisolone in early RA. (the activating:inhibiting FcR expression ratio was defined as the ratio of the sum of the MFIs of the activating CD64 + CD32a + CD16a divided by the MFI of the inhibiting CD32b).</p

Altered FcγR function in early RA.

<p>IgG1 and IgG3 IC-binding (A-B), ratio of IgG1-IC/IgG3-IC binding (C) and IgG1- and IgG3-IC stimulated TNFα-release (index) (D-E) in DMARD- and steroid naive early RA patients (<i>n</i> = 20) and in healthy controls (HC) (<i>n</i> = 33).</p

Effect of methotrexate and prednisolone treatment on monocytes and FcR receptors.

<p>Frequency and expression of CD14 (A), CD64 (B-C), IgG bound to CD64+ cells (D-E) and CD89 (F-G) on monocytes before and after 3–4 months of anti-rheumatic treatment in DMARD- and steroid naive early RA patients (<i>n</i> = 20). (FV = first visit, FU = follow up).</p

Soluble FcR levels in early RA are regulated by anti-rheumatic treatment.

<p>The plasma levels of sCD89 (A), sCD64 (B) and sCD16a (C) in healthy controls (HC)(n = 20), in patients with active polyarticular psoriatic arthritis (PsA) (n = 22), and in early RA patients (n = 19) before and after treatment with anti-rheumatics. (FV = first visit, FU = follow-up).</p

Expression of Fc gamma receptor (FcγR)IIb in healthy and rheumatoid arthritis (RA) synovia

<p><b>Copyright information:</b></p><p>Taken from "High synovial expression of the inhibitory FcγRIIb in rheumatoid arthritis"</p><p>http://arthritis-research.com/content/9/3/R51</p><p>Arthritis Research & Therapy 2007;9(3):R51-R51.</p><p>Published online 23 May 2007</p><p>PMCID:PMC2206344.</p><p></p> (a) FcγRIIb was sparsely expressed in the few healthy synovial biopsies that were positively stained by GB3. The arrows indicate FcγRIIb positive cells in the sub-lining synovial layer and tissue. (b) The IgG1 isotype control antibody did not stain the healthy synovium. (c,e) Positive FcγRIIb expression was found in all the stained RA synovial biopsies. FcγRIIb staining was observed in the synovial lining and sub-lining layers, perivasculary and inside lymphocyte infiltrates (e). (d) No staining of the RA synovium was observed when the anti-FcγRIIb monoclonal antibody was bound by recombinant human soluble FcγRIIb prior to staining. (f) Synovial FcγRIIb expression was significantly up-regulated in RA patients (= 10) compared to healthy individuals (= 5) (mean values of two independent observers, SEM and SK with standard error of the mean, *= 0.0104). DAB, diaminobenzidine. (Original magnification ×125.

Co-localisation of CD163 with Fc gamma receptor (FcγR)I, II, IIb and III

<p><b>Copyright information:</b></p><p>Taken from "High synovial expression of the inhibitory FcγRIIb in rheumatoid arthritis"</p><p>http://arthritis-research.com/content/9/3/R51</p><p>Arthritis Research & Therapy 2007;9(3):R51-R51.</p><p>Published online 23 May 2007</p><p>PMCID:PMC2206344.</p><p></p> Rheumatoid arthritis synovial tissue showed overlapping expression of the macrophage marker CD163 with the expression of FcγRI (a), FcγRII (b), FcγRIIb (c) and FcγRIII (d). The majority of the CD163 positive macrophages expressed FcγRIIb. However, note that a CD163 positive cell lacked FcγRIIb expression. (Original magnification ×400.