Biological activity of hamster interferon-gamma is modulated by the carboxyl-terminal tail.

The Syrian golden hamster (Mesocricetus auratus) is highly susceptible to a number of intracellular pathogens. Interferon-gamma (IFN-gamma), the primary macrophage-activating cytokine, plays a key role in the host defense against intracellular pathogens. The hamster IFN-gamma cDNA encodes a 174 amino acid protein that has an additional 17 amino acids at the carboxyl-terminus compared to IFN-gamma of mice and rats. A homologous C-terminal tail is also found in other non-murine rodents. The biological activity of hamster IFN-gamma had not been investigated previously so we first demonstrated the activity of native IFN-gamma in assays of IFN-gamma-induced receptor signaling and antiviral activity against vesicular stomatitis virus. We then tested the hypothesis that the C-terminal tail of hamster IFN-gamma could influence its biological activity. A truncated hamster IFN-gamma, in which the C-terminal 17 aa were removed by insertion of a stop codon at the position corresponding to the stop codon in the mouse sequence, had approximately 10-fold greater activity than the full length protein when measured in the two bioassays. Polyclonal and monoclonal anti-hamster IFN-gamma antibodies specifically inhibited this biological activity. Collectively, these data indicate that this unique structural feature influences the biological activity of hamster IFN-gamma.

Immunogenicity and protective efficacy of Plasmodium falciparum liver-stage Ag-3 in Aotus lemurinus griseimembra monkeys.

Three recombinant proteins spanning the Plasmodium falciparum liver-stage Ag-3 (LSA-3) were used to immunize Aotus monkeys. The proteins were delivered subcutaneously without adjuvant, adsorbed onto polystyrene 0.5 microm particles at a concentration of 2 microg per immunization. Control animals received glutathione-S-transferase formulated similarly. Animals were challenged as late as 5 months after the last immunization, by intravenous inoculation of 100,000 P. falciparum sporozoites of a strain heterologous to the one from which the immunogens were derived. Sterile protection was achieved in three of the five immunized monkeys but in none of four controls. Antibodies were at low titer, but reacted with the native parasite protein and were boosted by parasite challenge. Ag-specific IFN-gamma secretion was detectable in all LSA-3-immunized animals in response to the LSA-3-derived Ag. The protection was apparently associated with high levels of IFN-gamma production in response to in vitro recall Ag. These results lend support to the vaccine potential of LSA-3 indicated by previous results obtained in chimpanzees, as well as the value of yet another Ag-delivery system. They also support the value of the Aotus model for the pre-clinical development of pre-erythrocytic-stage vaccines.