Plasma pentraxin 3 in idiopathic inflammatory myopathies: a possible new biomarker of disease activity

Abstract

Pentraxin-3 (PTX3) is a component of humoral innate immunity with essential functions both in promotion and resolution of inflammation. We aimed to study the PTX3 in the plasma and in the muscle of patients with idiopathic inflammatory myopathies (IIM) and whether PTX3 may correlate with disease activity. Plasma PTX3 levels were assessed in 20 patients with IIMs, 10 dermatomyositis (DM), and 10 polymyositis (PM), compared to 10 patients with rheumatoid arthritis (RA) and 10 healthy donors (HDs) aged, sex, and body mass index matched. Disease activity in IIMs was assessed by Myositis Disease Activity Assessment Visual Analog Scale (MYOACT), while disease activity score on 28 joints (DAS28) was used for RA patients. Muscle histopathology and immunohistochemical (IHC) analyses were also performed. Mean plasma PTX3 levels were significantly higher in IIM patients than HDs (518 ± 260 pg/ml vs. 275 ± 114 pg/ml, P = 0.009). Linear regression analysis adjusted for age, sex, and disease duration showed a direct correlation between PTX3 and CPK levels (β: 0.590), MYOACT (β: 0.759), and physician global assessment of disease activity (β: 0.832) in IIMs. No association between PTX3 levels and DAS28 was found in RA. Global PTX3 pixel fraction was higher in IIM than HDs muscle, but a lower PTX3 expression was found in perifascicular areas of DM and in myofibers with sarcolemmal staining for membrane attack complement. PTX3 plasma levels were increased in IIMs and correlated with disease activity suggesting a possible role as biomarker of disease activity. PTX3 showed a different distribution in DM or PM muscle.

Keywords: biomarkers; disease activity; immunohistochemistry; myositis; pentraxin-3.

Graphical Abstract

Figure 1.

Values of plasma PTX3 levels in IIMs, RA, and HC subjects

Figure 2.

Representative light microscopy images (A, B, C) showing the muscle expression of PTX3 immunostaining in a control specimen (A), an anti-Mi2⁺ DM patient (B), and a PM/IMNM patient (anti-HMGCR positive) (C). PTX3 immunolocalizes in sarcoplasms of both HDs and IIM patients. Additional immunostaining appears in endomysial interstitial cells, but only in IIM patients (B and C, arrows). Scale bars: 70 μm. (D) Mean fraction of PTX3-positive pixel in IIM and HC subjects

Figure 3.

Representative confocal microscopy images showing double-positive PTX3/myosin heavy chain fast myofibers (A–F) and PTX3/C5b9 complement membrane attack complex (G–I) in control muscles (A, D), anti-HMGCR⁺ IMNM (B, G), and DM (C, E, F, H, I) patients. In healthy controls, several myosin heavy chain fast⁺ skeletal myofibers express low levels of PTX3 in their sarcoplasm (A, D); intermediate levels of PTX3 are shown by anti-HMGCR⁺ IMNM and seronegative DM muscle biopsies (B, C); in contrast, the PTX3 staining appears increased in anti-Mi2⁺DM (E, F) and anti-NXP2⁺DM (I). Perifascicular atrophy is characteristic of DM muscle pathology. The majority of atrophic myofibers express low or no levels of PTX3 (F, asterisk). Representative confocal microscopy images of the preferential localization of C5b9 complement membrane attack complex on sarcolemmas of myofibers expressing low (arrows) or no levels of PTX3 (G-I). Scale bars: A–F: 75 μm; G–I: 55 μm. DM: dermatomyositis; IMNM: immune-mediated necrotizing myopathy.

Figure 4.

Representative confocal microscopy images showing double-immunostained muscle tissues with anti-PTX3 and either anti-CD68 (A, B) or anti-CD31 (C–E) antibodies in control (A, C), anti-HMGCR⁺ IMNM (B, D), and anti-Mi2⁺ DM (E) muscle specimens. In healthy controls, expression of PTX3 is rarely revealed in CD68 putative macrophages/dendritic (CD68+) cells (A). Increased expression of PTX3 is revealed in CD68+ cells of anti-HMGCR⁺ IMNM (B). PTX3 does not localize in CD31⁺ endothelial cells (C-E). Perifascicular areas of an anti-Mi2⁺ DM muscles show atrophic myofibers with reduced PTX3 expression and CD31⁺ capillary depletion (E, asterisk). Scale bars: A, B: 15 μm; C–E: 75 μm. DM: dermatomyositis; IMNM: immune-mediated necrotizing myopathy.