Non-A, non-B hepatitis: is there more than a single blood-borne strain?

Fourteen chimpanzees were challenged with the Hutchinson strain inoculum that has been shown by many workers to produce non-A, non-B (NANB) hepatitis associated with characteristic cytoplasmic ultrastructural changes observable by electron microscopy. Nine of these animals had a history of definite NANB hepatitis induced by seven different human viral isolates; all of these animals resisted rechallenge. The five animals without a history of NANB hepatitis all developed definite histological changes associated with NANB hepatitis after challenge. Homologous rechallenge with a 100-fold higher infectivity titer was carried out in five of the nine chimpanzees. Cytoplasmic ultrastructural changes developed after challenge in two of these animals; the remaining three had evidence of possible mild reinfection on the basis of liver histopathology or mild elevations of transaminase or both. We conclude that most, if not all, blood-borne NANB isolates belong to a single class of agents and that this virus produces immunity to rechallenge, but this immunity may be overwhelmed by high-dose inocula.