antibodies how does your body fight infections?. introduction the body has to be ready to fight off...
TRANSCRIPT
AntibodiesHow does your body fight infections?
Introduction
• The body has to be ready to fight off anything which could do damage to it
• One of the ways that it can do this is by releasing lots of chemicals that will destroy anything in their path
• However, there’s an even more specific system that has been designed to target particular bugs that might get in – and this is where antibodies come in
Outline
• What is an antibody?• What does an antibody do?• Types of antibodies
What is an antibody?
• An antibody is a special group of proteins that acts like a label
• They are the main part of the humoral immune system, and they are produced by a special kind of cell called a plasma cell– Plasma cells are mature B
lymphocytes
What is an antibody?
• Each antibody is made up of– light chains– heavy chains– connected by disulphide
bonds
• The structure of the antibody is split into the Fab regions and the Fc region.
What is an antibody?
• The Fab regions– “Fragment antigen-
binding”– Connect to enemy
proteins– Different on different
antibodies
What is an antibody?
• The Fc region– “Fragment
crystallisable”– Connect to normal cells– Alerts immune cells to
the presence of an invader
What is an antibody?
invader
surface proteins
antibody
Immune cell
Fab region
Fc region
What do antibodies do?
• Antibodies are able to help prevent invasion from bacteria, viruses and other enemies in several ways– Neutralisation– Flagging– Opsonisation
What do antibodies do?
• Neutralisation– Invaders use proteins on
their surface to get into cells and cause damage
– Antibodies which coat surface proteins stop them from having this action
What do antibodies do?
• Flagging– By coating an invader,
the antibody acts like a flag to alert circulating immune cells to the present danger
– Immune cells connect to the Fc region of the antibody
What do antibodies do?
• Opsonisation– If an enemy is coated in
certain molecules, macrophages and other similar cells will eat up the invader
– Antibodies can cause this, and they can also stimulate complement, which is particularly good at causing it
Types of antibodies
• Antibodies exist in several different types• These are called isotypes• Each different type has a different type of heavy chain
• IgA• This is used in areas where there is
a layer of cells producing mucus, to stop infections growing in that area
• E.g. gut, respiratory tract and urogenital tract, saliva etc.
• Goes around in a pair (i.e. a dimer)
Types of antibodies
• Antibodies exist in several different types• These are called isotypes• Each different type has a different type of heavy chain
• IgD• This usually acts as a receptor on
the surface of B lymphocytes• It goes around on the surface of
these cells on its own (i.e. a monomer)
Types of antibodies
• Antibodies exist in several different types• These are called isotypes• Each different type has a different type of heavy chain
• IgE• Responds to things that the body is
allergic to (e.g. pollen)• Activates basophils and mast cells to
release histamine• Goes around alone (i.e. a monomer)
Types of antibodies
• Antibodies exist in several different types• These are called isotypes• Each different type has a different type of heavy chain
• IgG• This is the main antibody needed to
fight infection, causing autoimmunity and recognising re-infection
• The only antibody to cross the placenta• Shows if you have ever been exposed
to a particular infection• Goes around alone (i.e. a monomer)
Types of antibodies
• Antibodies exist in several different types• These are called isotypes• Each different type has a different type of heavy chain
• IgM• The antibody used mostly in the
‘acute phase’ immediate response, before a rise in IgG
• Shows whether you currently have a particular infection
• Goes around in group of five (i.e. a pentamer)
Types of antibodies
Summary
IgA Acts wherever there’s mucus, to fight infection (e.g. gut, lungs, genitourinary tract) Dimer
IgD Forms a receptor on the surface of B-lymphocytes Monomer
IgE Responds to things that the body is allergic to (e.g. pollen) Monomer
IgG This is the main antibody needed to fight infection, causing autoimmunity, and recognising re-infection Monomer
IgM The antibody used mostly in the ‘acute phase’ immediate response, before a rise in IgG Pentamer
Conclusion
• Humoral immunity is an important way in which the body fights off infection
• It is based around antibodies, which are groups of proteins that act like labels on invaders
• Antibodies fight infection in three major ways: neutralising enemies, flagging them up to immune cells, and coating them to help them get eaten
• Different isotypes of antibodies work in different ways and in different locations in the body
Any questions?Further reading:•DeFranco AL, Locksley RM, Roberston M (2007) Immunity: The Immune Response in Infectious and Inflammatory Disease. 5th Ed. Oxford University Press•Frank SA. (2002) Immunology and Evolution of Infectious Disease. Princeton University Press•Janeway CA Jr. (1993) How the immune system recognizes invaders. Scientific American. 269(3):72-79
For more information, don’t forget to visit www.blobs.org