Evading the Immune System
• Some pathogens can alter their surface antigens
to avoid immune system detection
• Influenza virus expresses 2 surface proteins:
hemaglutinin (HA) and neuraminidase (NA)
– Antigenic drift – point mutations to the HA and NA
genes
– Antigenic shift – sudden appearance of a new virus
subtype where HA and/or NA proteins are completely
different