Follow-up of hepatitis C virus infection in chimpanzees: determination of viraemia and specific humoral immune response.

Chimpanzees were inoculated intravenously with the H strain of hepatitis C virus (HCV), and analysed for viraemia using the polymerase chain reaction and for a humoral immune response using first and second generation anti-HCV ELISAs and an immunoblot assay (4-RIBA). In all seven chimpanzees studied, viraemia occurred several weeks before a significant increase in serum alanine transferase (ALT) activity, whereas the first circulating anti-HCV antibodies became detectable at the time of significant increase in ALT levels, provided the second generation ELISA or 4-RIBA was used. On the basis of the duration of viraemia the chimpanzees studied could be assigned to two different groups: those in which viraemia disappeared in conjunction with or shortly after seroconversion, and those remaining viraemic for many weeks after the appearance of antibodies. The clearance of HCV from the circulation did not correlate with the antibody pattern determined using 4-RIBA, i.e. the HCV-specific assays currently available do not enable us to predict whether an infected chimpanzee will develop persistent viraemia. Only two of the seven chimpanzees analysed developed anti-core protein (c-22) antibodies, which appeared at the same time as the first ALT peak, whereas all animals developed antibodies to the non-structural protein, c-33, and these antibodies persisted.

Reliable screening anti HIV with a new ultrasensitive ELISA procedure.

Based on the competitive principle a new enzyme linked immunosorbent assay (ELISA) was developed for the reliable detection of Anti HIV. By introducing a sequential competitive procedure a detection limit of Anti HIV was achieved, which exceeded Western blot analysis by factor 8 to 16 as measured with dilutions of 14 well characterized sera. The relevance of this ultrasensitive feature could be demonstrated by a sensitivity value of 100% as evaluated by testing a total of 218 confirmed Anti HIV positive sera as well as by clear cut positive results obtained with 3 specimens derived from early stages of HIV infection. Among a total of 1571 Anti HIV negative blood donations only 1 specimen turned out to be repeatable positive without staining of virus specific bands in Western blot. 117 potentially false positive reacting specimens, which tend to show false positive or ambiguous results in commercial ELISAs were all found negative with the ultrasensitive research assay. An interference of rheumatoid factors could not be demonstrated. The new research assay described in this study appears to represent a technique which combines all advantages of the competitive principle, namely excellent specificity and ease of handling and in addition shows a sensitivity, which significantly stands out against current assays and even confirmatory testing with Western blot.