Immunohistochemical identification of Propionibacterium acnes in granuloma and inflammatory cells of myocardial tissues obtained from cardiac sarcoidosis patients

Abstract

Background: Although rare, cardiac sarcoidosis (CS) is potentially fatal. Early diagnosis and intervention are essential, but histopathologic diagnosis is limited. We aimed to detect Propionibacterium acnes, a commonly implicated etiologic agent of sarcoidosis, in myocardial tissues obtained from CS patients.

Methods and results: We examined formalin-fixed paraffin-embedded myocardial tissues obtained by surgery or autopsy and endomyocardial biopsy from patients with CS (n = 26; CS-group), myocarditis (n = 15; M-group), or other cardiomyopathies (n = 39; CM-group) using immunohistochemistry (IHC) with a P. acnes-specific monoclonal antibody. We found granulomas in 16 (62%) CS-group samples. Massive (≥14 inflammatory cells) and minimal (<14 inflammatory cells) inflammatory foci, respectively, were detected in 16 (62%) and 11 (42%) of the CS-group samples, 10 (67%) and 10 (67%) of the M-group samples, and 1 (3%) and 18 (46%) of the CM-group samples. P. acnes-positive reactivity in granulomas, massive inflammatory foci, and minimal inflammatory foci were detected in 10 (63%), 10 (63%), and 8 (73%) of the CS-group samples, respectively, and in none of the M-group and CM-group samples.

Conclusions: Frequent identification of P. acnes in sarcoid granulomas of originally aseptic myocardial tissues suggests that this indigenous bacterium causes granuloma in many CS patients. IHC detection of P. acnes in massive or minimal inflammatory foci of myocardial biopsy samples without granulomas may be useful for differentiating sarcoidosis from myocarditis or other cardiomyopathies.

Fig 1. Representative samples with sarcoid granulomas.

An autopsy sample (A–C) and an EMB sample (D–F) from patients with sarcoidosis were stained with haematoxylin and eosin and immunostained with anti-P. acnes antibody. Many sarcoid granulomas were observed at the lower magnification (A, D). Small round bodies indicated by the black arrows (C, F) were found in some of epithelioid cells and multinucleated giant cells of these sarcoid granulomas by immunohistochemistry with anti-P. acnes antibody. Original magnification; ×200 (left), ×1000 (middle and right).

Fig 2. Representative samples with massive inflammatory foci.

Specimens obtained from autopsy samples in patients with CS (A–C), myocarditis (D–F), or other cardiomyopathy (G-I) were stained by haematoxylin and eosin and immunostained with anti-P. acnes antibody. Massive inflammatory cell infiltration was observed in samples from patients with CS (A, B), myocarditis (D, E), or other cardiomyopathies (G, H). Positive P. acnes immunostaining in macrophages of these inflammatory foci was detected only in samples from patients with CS (C; black arrows), and not in samples from those with myocarditis (F) or other cardiomyopathies (I). Original magnification; ×200 (left), ×1000 (middle and right).

Fig 3. Representative samples with minimal inflammatory foci.

Specimens obtained from autopsy samples and EMB samples in patients with CS (A–D), M (E–H), and CM (I–L) were stained by haematoxylin and eosin (A, C, E, G, I, and K) and immunostained with anti-P. acnes antibody (B, D, F, H, J, and L). Black arrows indicate positive P. acnes-immunostaining. Minimal inflammatory cell infiltration was observed in samples from all six patients. Even at the lowest inflammatory cell infiltration, positive P. acnes-immunostaining in macrophages of these inflammatory foci was detected in samples from patients with CS (B, D), but not in samples from those with M (F, H) and CM (J, L), regardless of the sample type. Original magnification; ×1000.

Fig 4. Schematic representation of granulomatous inflammation caused by P. acnes.

Granulomas begin as small collections of lymphocytes and macrophages with intracellular P. acnes (early inflammatory foci) as observed in the minimal or massive inflammatory foci of the CS-group samples. Macrophages change to epithelioid cells and become organized into a cluster of cells (immature granuloma). Further progression results in ball-like clusters of cells and fusion of macrophages into giant cells with or without remaining intracellular P. acnes (mature granuloma).