Since dendritic cells may play a key role in defenses against influenza virus infection, we examined the effects of recombinant hemagglutinin (HA) proteins derived from mouse-adapted H1N1 (A/WSN/1933), swine-origin 2009 pandemic H1N1 (A/Texas/05/2009), and high-pathogenic avian influenza H5N1 (A/Thailand/KAN-1/2004) viruses on mouse myeloid dendritic cells (mDCs). The results reveal that TNF-alpha, IL-12 p70, and MHC II expression were increased in mDCs after the treatments with recombinant HA proteins of H1N1 and H5N1. The specificity of recombinant HA treatments on mDC activation was diminished after protein K digestion. HA apparently promotes mDC maturation by enhancing CD40 and CD86 expression and suppressing endocytosis. No significant differences in mDCs activation were observed among recombinant proteins of H1N1 and H5N1. The stimulation of HA proteins of H1N1 and H5N1 on mDCs was all MyD88 dependent. These findings may provide useful information for the development of more effective influenza vaccines.
