Chagasic cardiopathy. Antibodies reacting with plasma membrane of striated muscle and endothelial cells

A direct binding assay for mitochondrial autoantibodies

A direct binding assay for the detection of mitochondrial autoantibodies (AMA) is described. The method has been standardised to use as antigen 1 mg/ml submitochondrial particles which are absorbed on to the surface of LINBRO S-MVC-96 microtitration plates as the solid phase. 125I-labelled antihuman immunoglobulin is used as the second antibody. The sensitivity achieved is greatly increased compared with immunofluorescence and complement fixation methods, with good discrimination between AMA negative and positive sera. The assay is rapid and has the advantages of a primary binding method. Two variations of the method are described. The first is reported as a "binding index' which is calculated from the binding shown by an unknown serum at 2 dilutions, and would be suitable as a screening procedure. Binding curves of doubling dilutions of a test serum give, in addition to the binding index, a titre which is defined as that dilution at which binding returns to the level of a normal serum. This is a longer procedure and more suitable as a research method.

Chagasic sera alter the effects of ouabain on isolated rat atria. Participation of adrenergic mechanisms

The effects of chagasic sera, containing an antibody (EVI antibody) which reacts with the plasma membrane of working myocardial cells, on "toxic" and "non-toxic" actions of ouabain upon isolated self beating or paced rat atria suspended in different media, were explored. Although ouabain produced a dose-dependent positive inotropic influence on atria suspended in Krebs-Ringer-bicarbonate (KRB) and in KRB plus normal human serum (KRB + NHS) it did not elicit any significant positive inotropic effect on atria beating in KRB plus EVI positive human chagasic serum (EVI(+)S). Additionally, EVI(+)S dose-response curves of classical signs of digitalis cardiac toxicity shifted to the left. The threshold concentration of ouabain required to elicit the onset of "toxic" effects was higher in control preparations (kept in KRB or KRB + NHS) than in EVI(+)S exposed preparations. (-)-Propranolol attenuated the overall toxic action of ouabain in EVI(+)S and facilitated its positive inotropic influence. In control media, the beta-adrenoceptor blocker failed to modify either the "non-toxic" or the "toxic" effect of ouabain. On the other hand, with control atria, subthreshold exogenous norepinephrine inhibited the positive inotropism of ouabain. The data suggest that an adrenergic mechanism is involved in the action of ouabain on cardiac tissue immersed in an EVI(+)S-containing solution. The foregoing results may explain the severe "toxic" effects observed with cardioactive glycosides when they are used in patients with Chagas' heart disease, even at low doses.

Population study of heterophile antibodies

Sera from 2,829 participants in a population health survey were tested for the presence of a heterophilic antibody, detectable by immunofluorescence. The antibody was found in 9.8% of the sera from women and in 12.4% of the sera from men. The age-specific prevalence of the antibody was relatively constant in women but rose steeply in men. The antibody occurred more frequently in individuals with a history of blood transfusion and in multiparous females. It is suggested that the antibody may result from immunization by a ubiquitous agent which can be transmitted by blood transfusion.

Argentine hemorrhagic fever. Alterations of the complement system and anti-Junin-virus humoral response

We investigated immunologic mechanisms and the role of complement in the pathogenesis of Argentine hemorrhagic fever, a disease caused by the Junin virus, a member of the arenavirus group. Total serum complement activity was reduced to 68 per cent of control values in patients with severe or moderate disease (P less than 0.001). C2, C3 and C5 values were also low (12 to 60 per cent) during the early acute period of the disease. However, serum C4 content was increased to 160 per cent of the control values in the same patients. Total complement activity returned to normal with clinical and laboratory recovery, at the time of detection of antibodies against Junin virus. C1q reactive material was found in four of 19 cases and no relation to the evolution of the disease could be established. These results suggest that immune complexes are not important in the pathogenesis of Argentine hemorrhagic fever, but that activation of the complement system has a role.