1. Antibodies How does your body fight infections?

2. 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

3. Outline What is an antibody? What does an antibody do? Types of antibodies

4. 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

5. 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.

6. What is an antibody? The Fab regions – “Fragment antigen- binding” – Connect to enemy proteins – Different on different antibodies

7. What is an antibody? The Fc region – “Fragment crystallisable” – Connect to normal cells – Alerts immune cells to the presence of an invader

8. What is an antibody? invader surface proteins antibody Immune cell Fab region Fc region

9. What do antibodies do? Antibodies are able to help prevent invasion from bacteria, viruses and other enemies in several ways – Neutralisation – Flagging – Opsonisation

10. 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

11. 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

12. 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

13. 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)

14. 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)

15. 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)

16. 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)

17. 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)

18. Types of antibodies Summary IgA Acts wherever there’s mucus, to fight infection (e.g. gut, lungs, genitourinary tract) Dimer IgDForms a receptor on the surface of B-lymphocytesMonomer 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

19. 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

20. 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