Immunization with Influenza Virus Hemagglutinin Globular Region Containing the Receptor-Binding Pocket

Abstract

The globular region of hemagglutinin (residues 91–261) membrane glycoprotein of influenza virus that encompasses the binding zone to the oligosaccharide receptor of target cells has been cloned by reverse transcriptase-polymerase chain reaction (RT-PCR). This protein segment (denoted HA91–261 peptide) induced significant immune response in mice. The serum antibodies and lung homogenates from the immunized mice cross-reacted with native virus particles. The cellular immunity was manifested by proliferative splenocyte responses and cytokine release indicating T helper type 1 activity. The plasmid DNA containing this segment (denoted pHA91–261) provoked, in addition, a significant cytotoxic T lymphocyte (CTL) response, whereas the HA91–261 protein fragment led to no such response. Both the DNA and the protein fragment of HA91–261 induced significant protection against viral challenge, although the immune response they induce might be along different pathways. Interestingly, the combined DNA priming-protein boosting immunization regimen did not induce protection against viral challenges even though it led to significant humoral immune responses similar to that induced by the peptide vaccine.