1. Lecture 10b:
Immune System

2. Definitions
Immunity- the body’s ability to repel or
destroy foreign substances, pathogens,
and cancer cells
Antigen- any molecule that stimulates an
immune response
Antibody- a molecule that recognizes and
binds to a specific antigen, neutralizing it

3. Basics
Immune system consists of lymphatic organs plus
individual cells
Red bone marrow
Thymus gland
Lymph nodes
Spleen
Nonspecific immunity- against pathogens in general
Specific immunity- against a specific antigen

4. Red Bone Marrow
Produces all types of blood cells
Lymphocytes (WBC’s) of two types
B cells- Produce plasma cells and memory cells
plasma cells- produce antibodies
memory cells- retain ability to produce antibodies
in the future
T cells- produce cytotoxic T and helper T cells
cytotoxic T- Kill virus infected and cancer cells
helper T- regulate immunity

5. Thymus Gland
largest in children; gets smaller when
we age
T cells mature here
Only ones that do not attack ‘self’ cells
are released ~5%

6. Lymph Nodes
Occur along lymphatic vessels
filter lymph as it passes through sinuses -
open spaces in the node
Macrophages line the sinuses- these are cells
that engulf and devour pathogens
Lymph nodes also contain many lymphocyes
Swell when fighting infection

7. Spleen
Filters the blood
Contains red pulp- where macrophages
remove debris (ie dead cells) and pathogens
Contains white pulp- where lymphocytes
fight infection and cancer
You can live without a spleen, but are more
susceptible to infection

8. Non-Specific Immunity
First line of defense against most
pathogens
Consists of:
Barriers to entry
Inflammatory Response
Complement System
Natural Killer Cells

9. Barriers to Entry
Skin and mucous membranes serve as a mechanical
barrier
Oil gland secretions on skin have some antibiotic effects
Upper respiratory tract has ciliated cells- the cilia move
mucous and trapped particles up out of the throat
constantly
Stomach has very acidic pH
Normal symbiotic bacteria limit or prevent growth of
anything else

10. Inflammatory Response
Response to damaged tissue- outwards signs of redness,
swelling, pain, warmth
Injury starts a chain reaction of events:
1. Damaged cells and mast cells release chemicals
(ex. histamine)
2. Capillaries dilate and become more permeable
3. Excess blood flow and permeability leads to
warmth and redness, swelling due to more fluids
leaking out of caps. Swelling pushes on nerve
endings, causing pain

11. Inflammatory Response
4. Neutrophils migrate to the site of injury- these are
ameboid WBCs that phagocytize http://
www.sciencefriday.com/videos/watch/10331
5. Macrophages also migrate to the site of injury-
stimulate production and release of many WBCs from
nearby bone marrow
6. Accumulation of dead and living WBCs, as well as
dead cells, can form pus
7. Macrophages that have been at the site also migrate to
the lymph nodes, to activate the body’s immune response

12. Complement System
Consists of blood plasma proteins
Assist, mediate, or increase several
different types of cells
May increase production of some types
of WBCs

13. Natural Killer Cells
Kill virus infected or cancerous cells by
cell-to-cell contact
Kill cells that do not have a ‘self’ protein,
which cancerous and virus infected cells
can loose

14. Specific Immunity
Specific defenses respond to antigens
Immunity is when the body can recognize
and destroy a specific antigen
Lymphocytes recognize an antigen because
they have membrane proteins that bind to the
antigen
B cells and T cells are the cells involved in
this part of the immune system

15. B Cells
Each B cell can only bind to one specific antigen- occurs on
a plasma membrane receptor (BCR)
When the antigen binds to it, the B cell divides and produces
Plasma and memory cells
Plasma cells then manufacture mass amounts of the
antibody and secrete it into the body- the antibody is
identical to the BCR
Memory cells are how long-term immunity is achieved
If the antigen is encountered again, the memory cells
divide and produce plasma cells

16. Antibodies
Once antibodies are released into the
lymph and blood circulation, they bind
to the antigens
The complex is then phagocytized, or
eliminated from the body

17. T Cells
T cells have receptors in the membrane
also, but they can not recognize an
antigen by themselves
An antigen presenting cell must show it
to them first
Two types of T cells: helper and cytotoxic

18. T Cells
Cytotoxic T cells bind to the target cell, and release
perforins that create pores in it
Then they release granzymes into the target cell, which
cause it to undergo aptoptosis and die
Helper T cells regulate immunity- have the ability to
stimulate cytotoxic T cells and B cells by releasing
cytokines
These are the primary cells that HIV infects,
leading to the body not being able to respond
properly to infections

19. Immunizations
Exposure to some diseases can lead to life-
long immunity, but not all
If it is possible, a vaccine is typically
possible
Vaccines usually made either from a dead
pathogen or part of it, or frequently from
just an antigen that is found on the
pathogen

20. Problems
Allergies
Immediate: caused by the allergen
binding to mast cells that release
histamines, causing an immune response
Delayed: poison ivy, etc.- probably caused
by memory T cells that are at the site of
contact with the allergen

21. Problems
Autoimmune disease- when the body
does not recognize ‘self’ and attacks its
own cells
Many examples, including MS,
lupus, rheumatoid arthritis
No cures for these, some drugs can
help

22. Problems
HIV/AIDS
HIV destroys helper T cells
Because T cells promote all the other cells in the
immune system, once they are too few in
number
Pretty much any pathogen/ cancer can take
hold
Death results from the secondary diseases that
the person is unable to fight