Antibodies Versus Bacteria

Immunoglobulin G is a type of antibody that circulates in the blood and recognizes foreign particles that might be harmful. Image Credit: U.S. National Library of Medicine

Harvard University researchers have discovered that the orientation of antibodies when binding to bacteria can increase the chances of survival for bacteria. An antibody or immunoglobulin (Ig) is a Y-shaped molecule that recognizes specific antigens (foreign substances) by identifying certain areas on the surface of the antigen. They typically bind to the foreign cell with their arm, or Fab regions. Once bound, the stalk or Fc region of the antibodies signal immune cells to destroy the foreign cell. The researchers discovered that Streptococcus pyogenes bacteria do a better job of surviving antibodies in saliva than in the blood.

Streptococcus pyogenes bacteria cause strep throat and typically invade the respiratory tract and skin. When antibodies bind to S. pyogenes, the bacteria secrete proteins that bind the Fc region of the antibodies so that immune cells can not detect their presence. The researchers discovered that antibodies in saliva typically attach to S. pyogenes with their Fc region. In the blood however, antibodies bind to these bacteria with their Fab regions. Using this orientation, immune cells quickly destroy the bacteria in the blood.

Learn more about this study, see:

• Antibody Orientation Matters (Science Daily)