Multinucleated giant cells undergoing apoptosis in experimental autoimmune myocarditis

Increased expression of caveolin-1 and -2 in the hearts of Lewis rats with experimental autoimmune myocarditis

The expression of caveolin-1, -2 and -3 was studied in the hearts of rats with experimental autoimmune myocarditis (EAM), to elucidate the involvement of caveolins in the pathogenesis of EAM. Western blot analysis showed that levels of caveolin-1 and -2 were significantly increased in the hearts of rats with EAM on day 14 post-immunization (pi), as compared to the hearts of normal controls (p < 0.05, normal controls vs. EAM). Caveolin-3 is already at a high level in control animals, so it does not increase further. Immunohistochemistry showed that caveolin-1 was expressed mainly in ED1-positive macrophages and in some cardiomyocytes and vessels in the EAM lesions. Caveolin-2 was expressed constitutively in the vascular endothelial cells of normal hearts, and its expression was enhanced in EAM rats, as compared with the normal control group. Caveolin-3 was expressed constitutively in the plasma membranes of cardiomyocytes, but not in the vascular endothelial cells and inflammatory cells in the EAM lesions. Our results suggest that the expression of caveolin-1 and -2 is increased in EAM lesions and that the increased expression of caveolin-1 stimulates second signals in affected cells, such as macrophages and some cardiomyocytes, in EAM rats.

Increased expression of phospholipase D in the heart with experimental autoimmune myocarditis in Lewis rats

The expression of phospholipase D (PLD) in the hearts of rats with experimental autoimmune myocarditis (EAM) was studied to elucidate the functional role of PLD in the pathogenesis of EAM. Western blot analysis showed that the level of the PLD1 isoform was significantly increased in the hearts of rats with EAM on days 14, 17 and 21 postimmunization (pi) (P < 0.01; control vs EAM at 14 pi, 17 pi and 21 pi). The phenotypes of cells exhibiting increased PLD1 expression were primarily inflammatory cells, including ED1 positive macrophages, in the inflammatory EAM lesions. Some cardiomyocytes also showed increased PLD1 immunoreaction in and around EAM lesions. Some PLD1-positive cells were also positive for proliferating cell nuclear antigen in some cardiomyocytes or terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling in some macrophages, suggesting that PLD1 positive cells have a capacity for proliferation or apoptosis depending on cell types in the target organ. Thus, it is postulated that increased expression of PLD1 in EAM may support an early inflammatory response in proliferating inflammatory cells, and its expression in cardiomyocytes may help them to survive by activation of survival factors in hearts with EAM.