PMC

 Localisation of IgM on cardiomyocytes in myocardial infarct and colocalisation of IgM, C3d, C5b–9, and C reactive protein (CRP) in the human heart. Localisation of IgM on cardiomyocytes in the heart of a patient who had died from acute myocardial infarction (AMI): (A) IgM deposited on the plasma membrane (arrow I), on cross striations (arrow II), and in the cytoplasm (arrow III) of jeopardised cardiomyocytes (original magnification, ×630); (B, C) high power view of IgM staining of the plasma membrane of jeopardised cardiomyocytes (arrows IV, V, and VI) (original magnification, ×1000). (D, H) Localisation of IgM; (E) localisation of complement factor C3d; (F) localisation of CRP; (I) localisation of complement factor C5b–9 in the heart of a patient who died after AMI (original magnification, ×100). (G) Negative staining using an IgM subtype monoclonal antibody against Leu7 (negative control).

A, detection of Ig µ and Ig κ transcripts in multiple cancer cell lines by semi-nested RT-PCR. HeLa and HeLa MR, cervical cancer cell lines; SW480, colon cancer cell line; U-2 OS, osteosarcoma cell line; HepG2, hepatic cancer cell line; 293 and 293T, human embryonic kidney cell lines. Raji, human B lymphocytic leukemia cell line, as positive control; GAPDH, internal control. B, flow cytometry study using mouse anti-human Ig µ mAb showed that IgM was localized not only on the plasma membrane but also in the cytoplasm of epithelial cancer cells, especially HeLa MR cells. Red line, isotype control IgG1; Blue line, anti-human IgM. C, Confocal microscopy analysis of HeLa MR cells using mouse anti-human Ig µ mAb showed that IgM was present both on the cell membrane and in the cytoplasm. Mouse IgG, as isotype control. D, whole IgM was detected in HeLa MR cells by non-reducing SDS-PAGE (without β-mercaptoethanol) and Western blot with goat anti-human Ig µ polyclonal antibody. Human IgM, as positive control. E, IgM expression was detected in HeLa MR cells by reducing SDS-PAGE (with β-mercaptoethanol) and Western blot with mouse anti-human Ig µ mAb. Human IgM, as positive control; β-actin, internal control. F, IgM was also detected in the cultural supernatant of HeLa MR cells by reducing SDS-PAGE and Western blot using mouse anti-human Ig µ mAb. Human IgM, as positive control; Medium, as negative control.

The cytoplasm of the nodular proliferating cells is faintly positive for kappa chain (a) but negative for lambda chain (b), indicating ISH-mediated kappa-chain monoclonality. The cytoplasmic IgM expression is identified immunohistochemically (inset)
ISH: in situ hybridization; IgM: immunoglobulin M

Localization of human IgM and IgG by immunogold EM. (A and B) EM images of cap59 cells grown in Sabouraud medium with IgM. (C to F) C. neoformans H99 grown in TCM with anti-human IgM 5-nm gold or with IgM labeled with anti-human IgM 5-nm gold. (D to F) Magnifications of cell shown in panel C to demonstrate binding of anti-IgM to vesicle-like structures. (G and H) C. neoformans H99 grown with IgG labeled with anti-human IgG 10-nm gold after 18 h of culture at 37°C, 5% CO₂, as described in Materials and Methods. Arrows indicate gold particle labeling. CP, capsule; CW, cell wall; CY, cytoplasm; st-v, structure-like vesicles.