1. Immune System Chapter 14

2. Immunity – the ability to resist infection and disease
Humans have two major types of defense mechanisms:
Innate (Non-specific) immunity
Adaptive (Specific) immunity

3. Overview of Innate and Adaptive Immune Responses

4. Innate (Non-specific) immunity
defense responses that do not distinguish between one threat and another
are present at birth
include: physical barriers (e.g. skin), phagocytic cells (neutrophils, monocytes, macrophages, eosinophils), NK cells (immunological surveillance), chemicals (interferon,complement system), inflammation, fevers, etc.
provides body with “non-specific resistance”

5. Adaptive (Specific) immunity
protection against specifically identified threats
usually develop after birth (“acquired”) 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

6. Adaptive (Specific) immunity
depends on coordinated activity of T & B lymphocytes (“T cells” & “B cells”)
T cells- involved in “cell-mediated (aka cellular) immunity
B cells- involved in “antibody-mediated (aka humoral) immunity”
usually produces a state of long-term protection known as “acquired immunity”

7. Acquired immunity actively comes about through exposure and response (production of specific T cells/production of specific antibodies) to a particular antigen.
Exposure can be through “natural” or “artificial” means.
naturally acquired active immunity – natural exposure results in immune response & development of long term immunity
artificially induced active immunity – deliberate “artificial” exposure to Ag (i.e. vaccine/immunization)

8. Short-term immunity can be passively gained through the transfer of pre-made antibodies.
Transfer can be through “natural” or “artificial” means.
naturally acquired passive immunity – antibodies transferred from mom  baby across placenta or in breast-milk
artificially induced passive immunity – administration of antibodies to fight disease after exposure to pathogen

9. Properties of Specific (Adaptive) Immunity
Specificity
Versatility
Memory
Tolerance

10. Properties of Adaptive Immunity
Specificity – T & B cells have specific membrane 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

11. 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 (APCs)” (ie. Macrophages, dendritic cells)
Once activated, some T cells attack the invader, & others stimulate the activation of B cells
Activated B cells mature into “plasma cells” which produce specific antibodies designed to destroy the particular antigen.
“memory cells” are created to ensure faster response to same antigen in the future

12. Overview of the immune response

13. Cell Mediated (a.k.a. Cellular) Immunity
In order for T lymphocyte to respond, they must first be activated through the process of “antigen recognition”
Antigen presenting cells (APCs) engulf (by phagocytosis) or remove (by pinocytosis) antigens in the body, or viral antigens are displayed on infected body cells
the antigenic fragments are displayed on the surface of APCs and body cells bound to special membrane receptors
These special membrane receptors on cells are called “MHC proteins” (major histocompatibility complex proteins), & are genetically determined (i.e. differ among individuals), allowing determination of “self vs. non-self”
Antigens bound to MHC proteins “tell” a T lymphocyte what the specific foreign invader is (i.e. a specific bacteria) so that the lymphocytes can mount a cellular defense

14. © 2013 Pearson Education, Inc.
Antigen Recognition
Antigen recognition occurs when a T cell
encounters an appropriate antigen on the surface of
another cell, bound to an MHC protein.
Infected cell
Viral or
bacterial
antigen
Class I
MHC
protein
Antigen
Inactive
cytotoxic
T cell
T cell
receptor
© 2013 Pearson Education, Inc.

15. Cell Mediated (a.k.a. Cellular) Immunity
Once a T cell is activated through antigen recognition, it will divide (clone) and differentiate into an army of T cells, which will include:
cytotoxic T cells
helper T cells
memory T cells
suppressor T cells

16. Cell Mediated (a.k.a. Cellular) Immunity
cytotoxic T cells (aka CD8 cells) - seek out the specific pathogen/infected cell that contains the targeted Ag & destroys it by secreting various chemicals
helper T cells (aka CD4 cells) – necessary for coordination of specific (adaptive) & non-specific (innate) 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 antibody producing plasma cells

22. Antibody Mediated (Humoral) Immunity

23. Summary Innate and Adaptive Immune Responses