Immunogenicity of a Recombinant Avian Influenza H2 Protein Using an Abdominal Inoculation Model in Chickens.

Background/objectives: Avian influenza represents a major threat to both animal and public health. Our group has tracked avian influenza viruses circulating in wild birds in Peru during the last 20 years. While most of these viruses are low-pathogenic avian influenza strains, some exhibit genetic changes that significantly diverge from common circulating viruses. We selected a highly divergent hemagglutinin H2 gene from a genetically characterized avian influenza virus to develop a recombinant protein using a baculovirus system.

Methods: We administered 5 µg and 20 µg doses of the recombinant H2 protein (rH2) into 3-week-old chickens using an abdominal cavity inoculation model to evaluate the activation of innate immune responses. Chickens were euthanized at 24 and 72 h post inoculation and an abdominal lavage was performed to harvest the abdominal cavity content.

Results: Infiltrating cells were counted and their cell viability was measured using an Annexin V/PI staining. At 24 h, a large proportion of infiltrating leukocytes were identified as heterophils, monocyte/macrophages and lymphocytes. These proportions changed at 72 h, with a decrease in heterophils and increase in monocyte and lymphocyte pools. We observed strong cellular activity in abdominal leukocytes at 24 h, with a decline in activation levels at 72 h. Cytokine expression suggested a tightly regulated immune response during the 72 h period, while a more sustained response was observed at the 20 µg dose. Antibody levels demonstrated the capacity of the rH2 protein to induce long-term responses.

Conclusions: These results revealed that the baculovirus-expressed rH2 protein induces a controlled immune activation, a long-term immune response, holding promise as a potential vaccine candidate for animal health.