Protective immunity and possible autoimmune regulation in amebiasis.

Hamsters were injected intradermally with axenic trophozoites of a pathogenic strain of Entamoeba histolytica, and controls similarly with culture medium. Localized lesions were produced in all animals injected with amebae. After the lesions healed all the animals were challenged intrahepatically with axenic amebae. Extensive liver abscesses were produced in all the controls, but a small abscess in only one of the vaccinated hamsters. In the protected animals the indirect hemagglutination antibody titers were high (I:512), while in the controls they ranged between 1:32 and 1:128. In the vaccinated hamster with the small abscess the IHA titer was 1:32. To investigate a possibility of autoimmune regulation in amebiasis, sera of hamsters with experimental amebic liver abscesses were acidified and tested by counter-current-immunoeletrophoresis against untreated autologous sera and amebic antigen. In most cases there was a direct correlation between the two titers. With human antisera in autologous systems there was reactivity against anti-amebic IgG antibodies. These experiments showed that autoimmune complexes may be present in cases of hepatic amebiasis. As in chronic hepatitis and some malignancies, it is possible that immune complexes have an immunoregulatory function in amebiasis.