Transcript Tissues and Organs

Antibodies
How 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 antigenbinding”
– 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?
Immune cell
Fc region
antibody
Fab region
surface proteins
invader
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