Infection and immunity
Infection and immunity

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Infection and immunity

Session 4: Immune defences against infectious diseases


In this part of the course you'll look at the body’s natural defences against pathogens – the infectious agents that cause disease. We describe how physical and chemical barriers keep pathogens from entering the body and how the immune system uses a range of specially adapted cells and molecules to attack pathogens that get past these barriers. One of these cell types is known as a B cell and it plays a vital role in producing antibodies to fight infection.

Watch the following video to learn more about this process and the role of B cells in producing an immune response to vaccination.

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CLAIRE ROSTRON: Antibodies are vital in our fight against infectious diseases because they're created by the body to recognise the presence of a pathogen invader. They're created by specialised parts of our immune system, called B cells. So called because they're found in the bone marrow.

Antibodies are very large molecules. While there are several different types, the most common of these found in the human body are made up of around 25,000 atoms. This large array of atoms tends to bunch and fold itself up to form crevices and bumps.

Every type of pathogen has at least one-- but often many more-- unique molecules known as antigens in their structure. Antigens are the parts of the pathogen that can be detected by antibodies, which work a bit like a pattern recognition system. We can imagine an antibody to be a bit like a lock devised from the crevices and bumps, such that only the right--shaped key will comfortably fit into the lock. But in this case, only the right antigen will fits into the bumpy and creviced antibodies that our bodies make.

The B cells, like typical animal cells, have cell membranes and they carry antibody molecules embedded by their tails in the cell membrane, with the antigen-binding sites facing outwards into the bodily environment. An antibody typically has two binding sites. When an antigen binds to the antibody at either site, it triggers the B cell to produce many more at the same antibody, which are then released into the bloodstream to circulate the body and detect further pathogens.

Antibodies themselves cannot kill pathogens. So strictly speaking, they cannot fight infection. They're simply a signalling mechanism that says to other cells of the immune system, here is a pathogen. Come and get it.

But their signalling is vital for immunity, since once the B cells have developed antibodies specific to an antigen, they can do so again but much faster. And this means that the recognition of a pathogen invader is much more efficient and the body cells can kill this pathogen invader before it replicates extensively and takes hold.

In this Open Learn course, you'll learn more about the B cells and other cells of the immune system.


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