Figure 5.

Intracellular proliferation of latent P. acnes followed by insoluble immune complex formation in sarcoid lymph nodes. Representative immunohistochemical features revealed by PAB or anti-IgM antibodies are shown below the illustrated macrophages with each stage of intracellular P. acnes manifestation. These findings imply that intracellular proliferation of latent P. acnes in paracortical macrophages triggers granuloma formation in sarcoidosis patients. PAB-reactive small round bodies bound with immunoglobulins (mainly IgM and IgA) are formed extracellularly and phagocytosed by sinus macrophages after release from paracortical macrophages with proliferating P. acnes that are free of immunoglobulins. Some of the P. acnes-derived immune complexes may escape local phagocytosis. All photos are original. Scale bar: 5 μm. HW, Hamazaki–Wesenberg.