The pathogenic effect of IgG4 autoantibodies in endemic pemphigus foliaceus (fogo selvagem).

Endemic pemphigus foliaceus, or fogo selvagem, is an autoimmune blistering skin disease caused by IgG autoantibodies to a desmosome-associated glycoprotein. We studied the IgG subclasses with autoantibody activity in serum from 29 patients with active disease and in the skin lesions of 18 patients by immunofluorescence, using IgG-subclass-specific monoclonal antibodies. The predominant disease autoantibodies present in all patients were of the IgG4 subclass. IgG1 and IgG2 autoantibodies were detected in low titer in the 29 patients: IgG1 in 23 patients and IgG2 in 9. IgG3 autoantibodies were not detected in the serum of any patient. Direct immunofluorescence testing of skin lesions showed a preferential deposition of IgG4 on the keratinocyte surface. The pathogenic effect of IgG4 was demonstrated by the passive transfer of fractions containing IgG4 autoantibodies from the patients to neonatal BALB/c mice. The disease of the patients was reproduced clinically, histologically, and immunologically in these animals. Only IgG4 autoantibodies were detected by direct immunofluorescence, bound to the epidermis in the lesions of the mice, and by immunoelectron microscopy at the keratinocyte surface. IgG4 has previously been reported to be a blocking or protective antibody because it has poor effector functions in vitro, as compared with the other IgG subclasses. The finding that it is the pathogenic autoantibody in fogo selvagem raises the possibility that it may also be important in other autoimmune disease.

Endemic pemphigus foliaceus (Fogo Selvagem).

Fogo selvagem presents our specialty with a unique situation. The disease is fundamentally identical to the pemphigus foliaceus that we are familiar with in North America, but there is impressive epidemiologic and circumstantial evidence that an environmental factor is producing this highly specific autoimmune phenomenon. If one can define this factor and investigate the mechanisms operative in the promotion of the disease, one would develop major new insights into both the normal function of the immune system and the specific disease state. Implications for understanding other autoimmune diseases are also obvious. However, to overcome the difficult logistics of studying these patients by modern techniques presents a formidable task. Hopefully, with the cooperation of interested investigators in both Brazil and the United States, these problems can be overcome.

In vivo studies of antibody dependent acantholysis.

The data that are being accumulated on the mechanisms by which pemphigus autoantibodies induce acantholysis in vivo conform that tissue injury in pemphigus is a complex phenomenon where several effector mechanisms may interact. Active research is being performed in many laboratories around the world, employing both in vitro and now in vivo models to further define this unique autoimmune disease.

Elevated thymosin alpha I levels in Brazilian pemphigus foliaceus.

Levels of thymosin alpha I in the sera of 37 patients with Brazilian pemphigus foliaceus (BPF) were measured using a competitive binding radioimmunoassay. The values were compared with 19 patients with other forms of pemphigus, 13 relatives of patients with BPF, 18 patients with other dermatological diseases, and 265 normal controls. We found that 27 (73%) of the patients with BPF had thymosin alpha I serum levels that were at least two standard deviations above the mean for normal individuals. The mean value for patients with BPF was significantly greater than any other groups studied. The thymosin elevation is similar to alterations seen in certain viral diseases and suggests that BPF is aetiopathogenically distinct from the forms of pemphigus.

Brazilian pemphigus foliaceus autoantibodies are pathogenic to BALB/c mice by passive transfer.

Brazilian pemphigus foliaceus (fogo selvagem) is a cutaneous blistering disease endemic to certain areas of South America that has distinctive epidemiologic features suggestive of an infectious disease transmitted by an insect vector. Patients with the disease have antiepithelial autoantibodies, both circulating in the serum and bound to lesional epidermis. In order to examine the possible pathogenic role of these autoantibodies, IgG from the sera of these patients was purified and injected into the peritoneum of neonatal BALB/c mice. Thirty-four of 46 mice (74%) receiving parenteral IgG fractions from these patients developed cutaneous lesions that were identical to the human disease by clinical, histologic, immunologic, and ultrastructural criteria. High-titer Brazilian pemphigus foliaceus sera produced lesions more consistently and rapidly than low-titer sera. When injections were discontinued, new lesions ceased to appear and old lesions resolved. The extent of disease correlated with the titer of human antiepithelial antibodies detected in the mouse serum (z less than 0.01). Similar concentrations of IgG fractions obtained from sera of unaffected Brazilians living in endemic areas and from American donors did not induce disease when injected into littermates. These results establish that the antiepithelial autoantibodies play an important role in the pathogenesis of the cutaneous lesions in Brazilian pemphigus foliaceus.