Friday, November 22, 2013

Scientists discover how seasonal flu typically escapes immunity

The three-dimensional structure of influenza virus
from electron tomography
It is that time of year again, flu season. Every year seasonal flu is responsible for severe illness, hospitalization and even death worldwide. In order to combat this worldwide health issue, flu vaccines are prepared that consist of inactivated flu virus from three major different types of flu virus that infect humans. This vaccine initiates an immune response which produces antibodies against these viruses which will have a protective effect when someone is exposed to the actual virus.

However, the flu virus is constantly evolving. Specifically, the outer coat changes and the antibodies that once were protective eventually become ineffective. Because of this constant change, the World Health Organization meets twice a year to decide whether or not to change the strains of flu virus which are included in the vaccine.

In the interest of better understanding how the seasonal flu virus escapes immunity a collaboration of scientists from around the world worked together on a project to understand the molecular basis for the changes that result in the loss of virus-specific antibody response. The results of this work are published in a recent issue of Science in a paper entitled: 'Substitutions Near the Receptor Binding Site Determine Major Antigenic Change During Influenza Virus Evolution'. In this study they found that changing even a single amino acid allows the virus to evade detection by antibodies. However, these changes occur at only 7 places on the virus coat, as opposed to the 130 places previously believed. All 7 of the sites where single amino acid changes occur are near the area where the flu virus binds to and infects host cells also known as the receptor binding site. This is somewhat surprising as the virus need to conserve the receptor binding site so that it can recognize and infect cells.

These scientists hope that this new information will help to improve flu vaccines!

Some information for this blog post was obtained from the Science Daily article: How Flu Evolves to Escape Immunity