Download Activity 1: Antibodies and the adaptive immune response

Activity 1: Antibodies and the adaptive immune response
The innate and adaptive immune system
You will already be aware of the immune system and have some understanding of how it
protects our bodies against pathogens such as viruses and bacteria. You may recall that it
can be divided into two parts: the innate and the adaptive (aka specific). The innate immune
system is our body’s first line of defense. The cells of the innate immune system are able to
recognise many of the molecules that are commonly found on the surface of pathogens. If
they detect these molecules the immune system is able to respond quickly, initiating an
inflammatory immune response to attract more cells and destroy the pathogen. However,
many viruses and bacteria have evolved ways of avoiding recognition or curbing the
inflammatory immune response, often by hiding the molecules that alert the innate immune
system or by ‘disguising’ themselves by mimicking the molecules displayed on the body’s
own cells. In this situation the innate immune system requires help from the cells of the
adaptive immune system that are much better equipped for identifying pathogens. The cells
responsible for this are a type of white blood cell known as lymphocytes. There are two main
types of lymphocyte: B cells and T cells. It is B cells that are responsible for producing
antibodies.
B cells and antibodies
Antibodies are small, y-shaped glycoproteins produced by B cells. The role of antibodies is
to recognize a small part of a pathogen known as an antigen and bind to it. By binding,
antibodies can prevent further replication of the pathogen and alert the immune system to
the pathogen’s presence so that other cells of the immune system can locate and destroy
cells that have been infected. Importantly, antibodies have the potential to recognize virtually
any pathogen. Antibodies are extremely diverse; over a lifetime humans produce over 10
billion different antibodies, each capable of binding a different antigen. This diversity is
necessary in order to be able to recognize such a broad range of pathogens. Each individual
B cell produces its own specific antibody. If an antibody recognises an antigen that it is able
to bind to, its B cell becomes activated (with help from a type of T cell known as a T helper
cell) and divides to create copies of itself which can produce more of the same antibody.
Some of these B cells survive for a long time and are able to respond quickly if the pathogen
ever enters the body again. These cells are called memory B cells and this ‘immunological
memory’ is the basis of vaccination.
(Image adapted from http://hashimotothyroiditis.weebly.com)
Follow this link to watch an animation explaining how genetic recombination allows us to
produce such a huge diversity of antibodies:
http://outreach.mcb.harvard.edu/animations/antibody.swf
Visit the HE+ forum to discuss your ideas about antibodies and the adaptive immune
response.