Download Immune System Basics

Immune System Basics
MHC 1
Antigens
 Immunity: The capacity to resist
infectious pathogens.
 Pathogens: Disease-causing
organisms
 Self vs. Non-self recognition
 Major Histocompatibility
Complex (MHC 1)
 Antigen- a particle or piece of
pathogen an immune system
recognizes as foreign.
1st Defense:
Non-specific Immune System

Reacts immediately after infection- does not need to ID
pathogen.
1. Barrier Defenses: Skin and Mucous membranes
2. Inflammatory Defenses:
 Histamine is released at the sign of damage
 Blood vessels leak fluid and WBC’s
3. Cellular and Molecular Defenses:
1. Macrophages: Use pocket transport (phagocytosis) to
destroy foreign particles.
2. Natural Killer Cells (NK): Release hydrolytic enzymes onto
target cells to rupture/destroy them.
3. Interferon
4. Complement
Final Defense:
Specific Immune System
Recognizes pathogens and develops a sustained
immune response.
Comprised of two parts:
1.
Cell- Mediated Response
2.
Humoral Response
White blood cells characters (lymphocytes):
Helper T cells (Th)
Killer T cells (Tc)
B cells
Macrophage
Specific Immunity- The Battle
Begins!
 Macrophages search body tissues for pathogens.
 Consume pathogens with phagocytosis, kill it with
lysosomes, and save the antigens.
 Antigens placed into MHC 2 receptors and
displayed on macrophage’s membrane.
 The macrophage is now considered an antigenpresenting cell (APC).
 http://www.youtube.com/watch?v=eVLO6j6Ho64
QuickTime™ and a
decompressor
are needed to see this picture.
Specific Immunity Cont.
 Macrophage chemically signals Helper T to attach to
it.
 Helper T attaches to the MHC 2 receptor (with
foreign antigen stuck in it) with its CD4 receptor.
 Helper T cells have incredible variety of receptors
that act like a “lock and key” in regards to the
displayed antigen.
 If the Helper T’s “key” fits the displayed antigen’s
“lock”, the Helper T is activated.
 Activation results in Helper T releasing cytokines
(ex. Interleukin)- chemicals that cause lymphocytes
to start mitosis.
Fig. 43-17
Antigenpresenting
cell
Peptide antigen
Bacterium
Class II MHC molecule
CD4
TCR (T cell receptor)
Helper T cell
Humoral
immunity
(secretion of
antibodies by
plasma cells)
Cytokines
+
B cell
+
+
+
Cytotoxic T cell
Cell-mediated
immunity
(attack on
infected cells)
Cell-Mediated Response
Seek and Destroy
 Body cells can be infected by viruses that will
hide inside the cell.
 As the virus reproduces inside cells, pieces of it
fall off and are put into new MHC 1 receptors that
the cell puts on its own membrane.
 Killer T cells can bind to an infected cell’s MHC 1
receptors with their CD8 receptors.
 If Killer T binds to MHC 1 receptors with antigen
attached, it releases a chemical called perforin.
 Perforin ruptures the infected cells membrane and
exposes the virus to other immune cells.
http://www.youtube.com/watch?v=1tBOmG0QMb
A&feature=related
Fig. 43-11
Top view: binding surface
exposed to antigen receptors
Antigen
Class I MHC
molecule
Antigen
Plasma
membrane of
infected cell
Fig. 43-18-3
Released cytotoxic T cell
Cytotoxic T cell
Perforin
Granzymes
CD8
TCR
Class I MHC
molecule
Target
cell
Dying target cell
Pore
Peptide
antigen
Fig. 43-12
Infected cell
Microbe
Antigenpresenting
cell
1 Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment
1
Class I MHC
molecule
1
T cell
receptor
(a)
2
2
Cytotoxic T cell
Class II MHC
molecule
T cell
receptor
2 T cell
recognizes
combination
(b)
Helper T cell
Humoral System
Bring in the artillery!
 B cells have receptors called antibodies
(100,000/cell).
 Different B cells have uniquely shaped antibodies
that match specific antigens.
 If a B cell’s antibody is able to bind with a specific
antigen (lock and key effect), the B cell receives a
message from Helper T’s to become activated.
 Activated B cells divide into Plasma B and
Memory B cells.
 http://www.youtube.com/watch?v=iDYL4x1Q6uU
&feature=related
Humoral System Cont.
 Plasma B cells produce and secrete 10,000
“keyed” antibodies per hour.
 Due to their shape, each can bind to several
antigens at once.
 Antigen/Antibody binding has three effects.




Neutralization
Macrophage signaling
Complement pore formation
http://www.youtube.com/watch?v=lrYlZJiuf18&feature=fvw
Fig. 43-21
Viral neutralization
Opsonization
Activation of complement system and pore formation
Bacterium
Complement proteins
Virus
Formation of
membrane
attack complex
Flow of water
and ions
Macrophage
Pore
Foreign
cell
Memory B cells
 These cells do not actively produce antibodies
 Instead, they remain in the bloodstream and
maintain their cell life cycle independently from
Th commands.
 If the same pathogen/antigen complex presents
itself in the future, these cells are already activated
and ready to produce antibodies.
 There are also Memory versions of Th and Tc cells
that serve a similar function.