the human immune system a simplified account of how your immune system works
TRANSCRIPT
The human immune system
A simplified account of how your immune system works
The immune response
starts with an antigen
approaching a cell of
the immune system,
here a macrophage.
antigen
macrophage
The Humoral Response - Activation Phase
The macrophage
engulfs the antigen
by phagocytosis. Lysosome containing enzymes
Antigen engulfed in vesicle
The vesicle containing an
antigen fuses with a
lysosome. The enzymes in the
lysozome break down the
antigen into fragments. This is
antigen processing.
antigen processing
Inside the macrophage,
the processed antigens
combine with special
class II MHC proteins.
These proteins can
move to the cell surface
membrane.
enzymes andproteins combining
Class IIMHC proteins
The antigen/MHC protein
complex is displayed on the
immune cell surface
membrane. The
macrophage is now known
as an antigen presenting
cell.
Processed antigen/MHC protein complex
Antigen-presenting cell
The next stage involves a helper T cell
(also know as a T-helper cell) as well as
the macrophage
T helper cell (TH)
macrophage (antigen-presenting cell)
receptors which bind to specificantigen/MHC protein complex
The receptors on the helper T cell enable
it to bind to the specific antigen-MHC
complex of the antigen presenting cell.
macrophage (antigen-presenting cell)
helper T cell
The binding of the helper T cell with the
antigen - MHC protein complex triggers the
macrophage to release proteins (cytokines)
that activate the helper T cell.
Cytokines from macrophage
The activated helper T cell now releases its own cytokines
Cytokines from helper T cell
The released cytokines stimulate the
helper T cell to reproduce and form a
clone of cells. Each new cell has the same
receptors as the original helper T cell, so
they are specific for the original antigen.
Clone of helper T cells
Another phase of the immune
response begins with a B cell.
The B cell has membrane
bound globular receptor
proteins (called IgM). Some of
these are specific for the same
antigen presented earlier by
the antigen presenting cell.
The Humoral Response - Effector Phase
antigen
B cell
IgM receptor
The B cell’s receptor
protein (an IgM) binds to
the antigen, and the cell
engulfs the antigen by
endocytosis.
IgM bound to antigen engulfed by cell
lysosome
The vesicle formed
inside the B cell fuses
with a lysosome. This
contains digestive
enzymes which break
down the antigen.
Fused vesicles containing antigen and enzymes from lysosome
B cell
Fragments of the
digested antigen
remain after
processing within the
vesicle.
Processed antigen
Class IIMHCprotein
The processed antigen
is attached to Class II
MHC receptors within
the B cell, and is
transported to the
membrane.
The MHC proteins form
a complex with the
antigen which is
displayed on the surface
of the B cell. It has
become another type of
antigen presenting cell
Antigen/MHC protein complex
B cell (antigen presenting cell)
A helper T cell from the clone of cells produced earlier specifically recognises the antigen presented by the B cell.
Antigen-presenting B cell
Helper T cell clone
The helper T cell cell binds to the antigen/MHC
protein complex displayed by the B cell.
This triggers the release of cytokines from the T cell.
Once the cytokines are released the helper T cell no
longer binds to the B cell.
Cytokines released by helper T cell
helper T cell binds to antigen complex on B cell
The cytokines released by the helper T
cell stimulate the B cell to divide and form
a clone of identical cells
B cell clones
The B cells continue to
divide and form two
groups of clones. Some
are long – lived MEMORY
cells. Most are antibody-
secreting PLASMA cells.
Plasma cells have
extensive endoplasmic
reticulum and many
ribosomes.
Memorycell
Plasma cells
Plasma cells are essentially antibody factories. They produce and secrete antibodies identical to those of the surface receptors of the original parent B cell
antibodies
Like the IgM surface receptors on the parent B cell,
the antibodies can bind to and inactivate the
antigens, forming an antibody-antigen complex.
This complex makes it easier for other white blood
cells to engulf the antigen (phagocytosis).
Antibody-antigen complex