Experimental autoimmune myocarditis in the Guinea pig

Summary: Male and female Guinea pigs underwent immunisation with heterologous heart protein (rat heart), complete Freund's adjuvant and pertussis vaccine (immunised) or normal saline (control) at weekly intervals for 6 weeks, and were subsequently studied. In vivo intracardiac pressures, cardiac outputs, blood volumes, in vitro pressure-volume relations, left ventricular collagen contents, light microscopy, direct immunofluorescence, lymphocyte stimulation studies, and serology for circulating anti heart antibody (haemagglutination and radioimmunoassay) were performed. Immunised Guinea pigs studied between 5 and 8 weeks following the immunisation protocol demonstrated a 44% increase in LVEDP (p<0.005), an increase in right atrial pressure (p<0.001), although no change in aortic pressure or cardiac output when compared with controls. Left ventricular weight was increased 20% (p<0.001), and in vitro left ventricular volume by 34% (at 8 mmHg distending pressure, p<0.001). Lung wet weight was increased 44% (p<0.005), and left ventricular collagen content increased 60% (p<0.001). Cultured lymphocytes from treated Guinea pigs demonstrated a 1.5- to 4.5-fold (dependent upon proximity to last immunisation) increase in radiolabeled thymidine uptake when incubated with Guinea pig heart protein compared to controls (p<0.001), and circulating anti Guinea pig heart antibodies were detected by haemagglutination and radioimmunoassay. Histological examination of the left ventricles revealed inflammatory cell infilltration and myocyte increase to varying degrees in 15 of the 18 treated animals. We conclude that inflammatory, probably immune-mediated, chronic myocarditis can be produced in the Guinea pig.