Antibodies

Antibodies

When a foreign antigen is detected by the immune system, antibodies specific to this antigen are produced as part of the specific immune response and help neutralise and destroy pathogens. 

Click on IMMUNO below to see basically how plasma cells produce antibodies to help eliminate bacteria. 

Antibody structure

Antibodies are immunoglobulins. These are complex proteins made by plasma cells. 

Simple antibody structure (you need to know this!)

Complicated antibody structure (you don't need to know - but to help you remember immunoglobulins are polypeptide based. 

Antibodies are specific to a particular antigen. 

How do Antibodies work?

Most antibodies work by attaching onto a pathogen carrying the matching antigen. This alerts other members of the immune system to the presence of the antigen (and consequently the presence of the pathogen). 

Opsonisation

Opsonins - A type of antibody that that binds to an antigen and act as 'docking sites' for a phagocyte. They allow the phagocytes to identify the pathogen, bind to it and carry out phagocytosis. 

Opsonins can be 

• Specific - only bind to specific antigens. 
• This is especially useful if the antigen that the antibody binds to, is used by the pathogen to attach to the host cells that they invade.  The binding of the antibody therefore puts this molecule out of action and the pathogen is unable to bind and invade the host cell as a result. This is called neutralisation. 

• Non-specific - bind to any molecules that are not found in the host, for example they could bind to the peptidoglycans found in all bacterial walls.

Agglutinins 

Agglutinins - Antibodies that cause pathogens to stick together.

The antibodies have 2 binding sites for an antigen, so the antibody can 'crosslink' the pathogens together in clumps. If many antibodies are involved this is called agglutination. 

Once the pathogens are clumped together;

• The pathogens may not be able to carry out their attack strategy as they are bound to many others. 
• The pathogens are clumped together so they are more easily taken in by phagocytes. This works very well on viruses. 

Anti-toxins

Some pathogens release toxins that harm the cells of the host. There are antibodies called 'anti-toxins' that binds to these molecules and render them inactive.

The primary and secondary response. 

Antibodies are produced each time an organism is infected with a particular pathogen and an antigen is detected. 

Primary  response

The first time an infecting agent is detected in a host the immune system, the plasma cells that make that particular corresponding antibody are activated, multiplied and antibodies are produced. 

It usually takes a few days for enough cells to be activated and antibodies to be made so the host feels the symptoms of the illness. When there are enough antibodies in the blood, the host can start to combat the disease. Once all the pathogens have been destroyed or neutralised, this initial wave of antibodies disappear. 

Secondary response

The antibodies do not stay in the blood. Instead there are B memory cells and T memory cells, specific to the same antigen that keep circulating in the blood. These are able to respond very quickly to the antigen if if the pathogen invades the same host. The antibodies produced in this second wave are produced rapidly and in a much higher concentration. There are enough antibodies in the blood very quickly after the second infection so the pathogens are neutralised or destroyed before the host feels any symptoms.