1. Immune System Chapter 14

2. Humans have two major types of defense mechanisms: Non-specific defenses & Specific defenses
do not distinguish between one threat and another
are present at birth
include: physical barriers (e.g. skin), phagocytic cells, inflammation, fevers, etc.
provides body with “non-specific resistance”

3. Specific defenses
protect against specifically identified threats (i.e. may defend against one particular bacterial infection but not a different one)
most develop after birth upon exposure to an antigen (Ag); an antigen can be a pathogen (disease-causing organism), foreign protein (e.g. toxin), abnormal or infected body cell, foreign tissue transplant
specific defenses produce a state of long-term protection known as “specific resistance” or “Immunity”

4. Immunity depends on coordinated activity of T & B lymphocytes
T cells- involved in “cell-mediated (aka cellular) immunity”; defense against abnormal cells & intracellular pathogens
B cells- involved in “antibody-mediated (aka humoral) immunity”; defense against pathogens (Ag’s) in body fluids (blood/lymph)

5. Overview of Immunity
Fig )

6. Immunity is either “innate” or “acquired”
Innate Immunity
present at birth
independent of previous exposure to Ag
genetically determined
species dependent

7. Acquired Immunity
arises throughout life by active or passive means

8. Active immunity – development of resistance (i. e
Active immunity – development of resistance (i.e. antibody (Ab) production) to specific disease secondary to exposure to specific Ag (pathogen)
naturally acquired active immunity – natural exposure results in immune response & development of long term immunity
induced (artificial) active immunity – deliberate “artificial” exposure to Ag (i.e. vaccine/immunization)

9. Passive immunity – development of immunity due to transfer of “pre-made” antibodies
naturally acquired passive immunity – Ab’s transferred from mom  baby across placenta or in breast-milk
induced (artificial) passive immunity – administration of Ab’s to fight disease after exposure to pathogen

10. Properties of Immunity
Immunity has four general properties:
Specificity
Versatility
Memory
Tolerance
Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

11. Properties of Immunity
Specificity – T & B cells have specific receptors that will allow them to only recognize & target a specific Ag; this process is known as “antigen recognition”
Versatility – millions of different lymphocyte populations, each with specific Ag recognizing receptors; allows for “anticipation” of potential Ag’s
Memory – after initial exposure, long term acquired immunity occurs through the production of memory cells; secondary exposure results in stronger faster response to previously recognized Ag
Tolerance – immune cells recognize self-antigens & “tolerate” (ignore) them, only going after foreign (non-self) Ag’s

12. Overview of the immune response
The purpose of the immune response is to inactivate or destroy pathogens, abnormal cells & foreign molecules (such as toxins)
In order for the response to occur, lymphocytes must be “activated” by the process of antigen recognition
T cells are usually activated first, & then B cells. T cells mainly rely on activation by phagocytic cells collectively known as “antigen presenting cells (APC’s)” (ie. Macrophages, dendritic cells)
Once activated, T cells both attack the invader, & stimulate the activation of B cells
Activated B cells mature into “plasma cells” which produce specific antibodies designed to destroy the particular antigen.

14. Cell Mediated (a.k.a. Cellular) Immunity
In order for T cells to respond, they must first be activated by exposure to an antigen
antigen is bound to membrane receptors of phagocytic antigen presenting cells (APC’s) (“antigen recognition”)
These membrane receptors on cells are called “MHC proteins” (major histocompatibility complex proteins), & are genetically determined (i.e. differ among individuals)
Antigens bound to MHC proteins “tell” the T lymphocyte what the specific foreign invader is (i.e. a specific bacteria) so that the lymphocytes can mount a cellular defense

15. Cell Mediated (a.k.a. Cellular) Immunity
Once a T cell is activated by the presentation of the combined MHC/Ag, it will clone (by mitosis) & differentiate into:
cytotoxic T cells
helper T cells
memory T cells
suppressor T cells

16. Cell Mediated (a.k.a. Cellular) Immunity
cytotoxic T cells – seek out the specific pathogen/infected cell that contains the targeted Ag & destroys it by secreting various chemicals
helper T cells – necessary for coordination of both specific & non-specific defenses, as well as for stimulating both cell-mediated & antibody-mediated immunity.
In cell-mediated immunity they release chemicals (cytokines) that strengthen the activity of cytotoxic T cells.
In antibody-mediated immunity they release cytokines that stimulate activated B cell division & differentiation into plasma cells

17. Cell Mediated (a.k.a. Cellular) Immunity
memory T cells – remain “in reserve” so if same Ag appears, these cells can immediately differentiate into cytotoxic & helper T cells, causing a swift secondary response to the invasion
suppressor T cells – activated more slowly than the other T cells; inhibit the response of the immune cells to prevent potential “autoimmune” response

18. Activated T cells clone & differentiate into: Cytotoxic T cells
Helper T cells
Memory T cells
Suppressor T cells
Direct physical &
chemical attack
stimulate
B cell activation
ANTIGENS
bacteria
viruses
SPECIFIC DEFENSES
(Immune response)
CELL MEDIATED IMMUNITY
APC’s phagocytize Ag & activate T cells
Prevent autoimmune response
Antigens
Remain in reserve
bacteria
viruses

19. Antibody Mediated (Humoral) Immunity
The body has millions of different B cell populations, each B cell has its own particular antibody (Ab) molecule (transmembrane protein) within its cell membrane
When the corresponding Ag invades the interstitial fluid surrounding the B cell, the Ag binds to the Ab molecule, & is taken into the cell, eventually being displayed on the B cell’s MHC protein. The B cell is now “sensitized”

20. Antibody Mediated (Humoral) Immunity
Helper T cells (that had been previously activated to the same Ag) then attach to the sensitized B cells & activate them by secreting chemicals (cytokines)
Cytokine secretion results in B cell cloning & differentiation into plasma cells & memory cells

21. Antibody Mediated (Humoral) Immunity
Plasma cells produce millions of copies of antibodies which are released into the blood & lymph
Antibodies seek out & bind to the Ag forming an “Ab-Ag complex”, eventually leading to the elimination of the antigen by various means
Memory cells remain in reserve to respond to any subsequent exposure by the same Ag. Upon secondary exposure, memory B cells quickly differentiate into Ab producing plasma cells

23. Antibody Mediated (Humoral) Immunity

24. Review of Immune Response