2.4 CELL RECOGNITION
AND THE IMMUNE SYSTEM
Cell recognition
Non-
specific
response
Specific
response
Physical barriers
e.g. skin
Phagocytosis
Chemical
barriers e.g.
stomach
acid
Phagocytes = type of
white blood cell
Chemoattractant
s from pathogens
or abnormal
cells Phagocytes
recognise the
pathogen and
ingest it
Phagosome
Lysosomes release
lysozymes into the
phagosome
Phagolysosome
Pathogen is
hydrolysed
Contents are
released
(exocytosis) or
absorbed
Proteins on
cell
membrane
Allow the immune
system to recognise
own cells and non-
self cells
Pathogens Cells from another
membrane of same species
Toxins
Abnormal body
cells e.g.
cancer cells
Antigen -
molecule
recognised as
non-self
Causes an
immune
response
Cell-mediated
response
Humoral
response
Antigen-presenting
cells
Helper T cells
have receptors
specific for the
antigen
Activation
and clonal
expansion
Stimulates
cytotoxic T cells,
B cells and
phagocytes
Cytotoxic cells
kill infected or
abnormal cells
Within cells
Within body fluids
B cell with antibody
specific for antigen
presents foreign
antigen on cell
surface
Helper T cell
with specific
receptor binds
to B cell Clonal
expansion of
B cells
Plasma B cells
produce secrete
antibodies
Memory B
cells
Divide rapidly upon
re-infection and
become plasma
cells
One B cell
produces one
type of
antibody
Monoclonal
antibodies
ELISA test
Basis of active
vaccination
HIV and
AIDS
https://bit.ly/pmt-cc
https://bit.ly/pmt-cc
