Download Adaptive immunity - Dr. Jerry Cronin

Adaptive Immunity
• Substances recognized as foreign that provoke
an immune response are called antigens (Ag).
• Adaptive immunity describes the ability of the
body to adapt defenses against the antigens of
specific bacteria,
viruses, foreign tissues…
even toxins (think of the
snake handler who
becomes immune to the
venom of snake bites).
Adaptive Immunity
• Two properties distinguish between adaptive
immunity and innate immunity:
1. Specificity for foreign molecules which act as Ag
• this involves distinguishing self-molecules (normal, not
antigenic) from nonself molecules
2. Memory forpreviously
encountered Ag
Adaptive Immunity
• Not all foreign substances are antigenic: We
don’t make antibodies to glass, for example.
Molecules, or parts of molecules tend to be
antigenic if they are:
• Foreign – not ourselves
• Organic
• Structurally complex (proteins are usually complex
and form many of the most potent antigens)
• Large (high molecular weight)
Adaptive Immunity
• Antigens can have multiple antigenic
determinants called epitopes.
• Each epitope is capable of producing
an immune response.
• Entire microbes may act as an
antigen, but typically just
certain small parts (epitopes) of
a large antigen complex triggers
a response.
Antigens can have multiple
antigenic determinants called
epitopes. Each epitope is capable
of producing an immune response.
Adaptive Immunity
• The adaptive immune response cannot get
started without the aid of the nonspecific
phagocytosis that occurs in the innate immune
response.
• The phagocytic cells that initiate the process are
called antigen presenting cells.
Adaptive Immunity
• Antigen-presenting cells (APCs) are mostly
dendritic cells and macrophages, and they
link the innate immune system
and the adaptive immune system.
– Dendritic cells are usually found
in tissues in contact with the
external environment, and they
are the most potent of the
antigen-presenting cell types.
Dendritic cells grow branched
projections called dendrites that
give the cell its name. However,
these do not have any special
relation with neurons which
possess similar appendages
Adaptive Immunity
• As an antigen-presenting cell engulfs and
destroys a foreign invader, it isolates
the antigens those cells
“display”.
• The APC then presents the foreign
Ag to a specific T lymphocyte
called a helper T cell
(also known as a CD4 cell) .
Processed Ag
is presented
Adaptive Immunity
• Once stimulated by antigen
presentation, helper T cells
become activated.
• Activated helper T cells are
capable of activating other
lymphocytes to become T
cytotoxic cells (CD8 cells) which
directly kill foreign invaders and B
cells (which make antibodies that
kill or helps kill foreign invaders).
Adaptive Immunity
• Activated B and T cells form the two arms of the
adaptive immune response: Antibody-mediated
immunity and Cell-mediated
immunity.
• Helper T cells aid
in both types, and
both types work
together to form
specific bodily
defenses.
The Innate and Adaptive Immune systems are depicted
Adaptive Immunity
• Cell-mediated immunity involves the production of
cytotoxic T cells that directly attack invading pathogens
(foreign invaders with Ag harmful to us – particularly
intracellular pathogens and some cancer cells).
• Suppressor and memory T cells are also produced.
• Antibody-mediated immunity involves the production of B
cells that transform into antibody making plasma cells.
• Antibodies (Ab) circulate in extracellular fluids.
• B memory cells are also produced.
Adaptive Immunity
• B-cells can be activated by
direct recognition of antigen
through B-cell receptors or
through T-helper cell
activation.
• Activated B-cells undergo
clonal selection to become
antibody producing plasma
cells.
Adaptive Immunity