Question

4. You are studying a new bacterial infection. You have evidence that people are infected by a bacterium; however, you cannot detect any antibodies in the infected individuals to the bacterium. What could be happening?

Answer 1

Antigens are proteins that are found on the surface of the pathogen. Antigens are unique to that pathogen. The whooping cough bacterium, for example, will have different antigens on its surface from the TB bacterium. When an antigen enters the body, the immune system produces antibodies against it. Antibodies are always Y-shaped. A type of white blood cell called a lymphocyte recognizes the antigen as being foreign and produces antibodies that are specific to that antigen. Each antibody has a unique binding site shape which locks onto the specific shape of the antigen. The antibodies destroy the antigen (pathogen) which is then engulfed and digested by macrophages.

Once a person has had a disease they don’t normally catch it again because the body produces memory cells that are specific to that antigen. The memory cells remember the microbe which caused the disease and rapidly make the correct antibody if the body is exposed to infection again. The pathogen is quickly destroyed preventing symptoms of the disease occurring.

As mentioned earlier the immune system of the host has to detect the antigen entering is foreign to the host and thus can a cascade of immune response be generated. However, some bacteria have evolved to these immune responses by masking their antigen surface thus the immunosurveillance within the host fails to detect the entered bacteria and therefore cannot generate antibodies against it.