1. The Immune System
Class 1

2. Introduction Vertebrates have three levels of defenses
1. The Integumentary System
Skin and mucous membranes provide first line of defense
2. Nonspecific (innate) Immune System
Acts very rapidly after onset of infection
3. Specific Immune System
Eliminates microbes that escaped the second line of defense 2 2

3. Integumentary system The skin is the largest organ of the body
Provides a nearly impenetrable barrier, reinforced with chemical weapons
Oil & sweat glands give skin a pH of 3-5
Lysozyme breaks bacterial cell walls
Also contains many normal flora
Non-pathogenic microorganisms that out-compete pathogenic ones
Composed of Epidermis, Dermis, and Subcutaneous layers. 3 3

4. Mucosal Epithelial Surfaces
The digestive, respiratory and urogenital tracts are lined by mucous membranes
-Cells secrete mucus which traps microbes
Digestive tract
-Salivary lysozyme; acidic stomach
Respiratory tract
-Ciliary action
Urogenital tract
-Acidic urine 4 4

5. Nonspecific Immunity
The nonspecific or innate immune system consists of cellular and chemical devices that respond to any microbial infection
-The response is quite rapid
Among the most important defenses are three types of leukocytes (white blood cells) 5 5

6. Leukocytes Macrophages Large, irregularly shaped cells
Kill microbes by phagocytosis
Mature from monocytes that enter tissues from the blood
Neutrophils
The most abundant circulating leukocytes
First to appear at site of damage/infection 6 6

7. Leukocytes Natural killer (NK) cells
Destroy pathogen-infected and cancer cells by causing programmed cell death or apoptosis
Produce perforins and granzymes
Immune surveillance 7 7

8. The Inflammatory Response
Inflammation involves several body systems
Injured cells release chemical alarms, including histamine and prostaglandins
Cause nearby blood vessels to dilate and increase in permeability
Promote phagocyte accumulation
Hallmark signs = Redness, warmth, swelling, pain, and potential loss of function
Interleukin-1 (IL-1) causes fever. 8 8

9. The Inflammatory Response9 9

10. Complement
The complement system consists of about 30 different proteins that circulate in the blood in an inactive form
-Upon pathogen encounter, a cascade of activation occurs
-Some proteins aggregate to form a membrane attack complex (MAC) on surface of pathogen
Pore
Fluid
Membrane
of invading
microbe
Complement
proteins 10 10

11. Interferon
Interferons (IFN) are proteins that play a key role in body defense
-Three major types: IFN-a, IFN-b, IFN-g
-IFN-a and IFN-b are produced by almost all body cells in response to viral infection
-Induce degradation of viral RNA
-IFN-g is produced only by T-lymphocytes and natural killer cells
-Protects from infection and cancer 11 11

12. The Specific Immune System
The scientific study of immunity began with Edward Jenner in 1796
-Observed that milkmaids who had cowpox rarely experienced smallpox
-Inoculated individuals with fluid from cowpox vesicles to protect them from smallpox
Vaccination 12 12

13. Antigens
An antigen is a molecule that provokes a specific immune response
-May be components of microorganisms or proteins/glycoproteins found on surface of red blood cells or transplanted tissue cells
A single protein may have many different antigenic determinants or epitopes
-Each can stimulate a distinct immune response 13 13

14. Lymphocytes
Lymphocytes are leukocytes with surface receptors for antigenic determinants
Direct an immune response against either the antigen or the cell that carries it
When a naïve lymphocyte binds a specific antigen for the first time, it gets activated by a process called clonal selection
Produces a clone of cells: some respond immediately, others are memory cells 14 14

15. Lymphocytes B lymphocytes or B cells
Respond to antigens by secreting antibodies or immunoglobulins (Ig)
Participate in humoral immunity
T lymphocytes or T cells
Regulate other immune cells or directly attack cells that carry specific antigens
Participate in cell-mediated immunity 15 15

16. The Specific Immune System
The four characteristics of the specific, or adaptive, immune response are:
-1. Specificity
-2. Diversity
-3. Memory
-4. Ability to distinguish self from non-self 16 16

17. Acquisition of Specific Immunity
Immunity can be acquired in two ways
Active immunity results from activation of an individual’s own lymphocytes
Pathogen infection or vaccination
Passive immunity results from obtaining another individual’s antibodies
Transfer of maternal antibodies across placenta 17 17

18. Organs of the Immune System
All cells are created in a process called hematopoiesis.
Organs of the immune system consist of the:
Primary lymphoid organs
Bone marrow and thymus
Secondary lymphoid organs
Lymph nodes, spleen, and mucosal- associated lymphoid tissue (MALT) 18 18

19. Primary Lymphoid Organs
The bone marrow is site of B cell maturation
Each B cell has about 105 Ig molecules on its surface, all with the same specificity
However, different B cells will have different specificities
B cells recognize epitopes directly
Any lymphocytes that are likely to bind to self-antigens undergo apoptosis 19 19

20. Primary Lymphoid Organs
The thymus is the site of T cell maturation
Each T cell has about 105 identical T-cell receptors, or TCRs on its surface
Recognize epitopes only if they are combined with major histocompatibility complex (MHC) peptides
Lymphocytes that cannot bind MHCs, or that bind self-MHC/self-peptide too tightly undergo apoptosis
T cells come in two flavors—Cytotoxic T (Tc or CD8) and Helper T (TH or CD4) 20 20

21. Immune Responses
The first encounter with a foreign antigen is called the primary immune response
Only few B or T cells can recognize antigen
The second encounter is called the secondary immune response
This time there is a large clone of memory cells that can recognize the antigen
Immune response is more effective 21 21

22. Exposure to cowpox This interval may be years Amount of antibody
Time
IgM
IgG
This interval
may be years
Secondary response
Primary response
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Amount of antibody 22 22

23. Autoimmunity The acceptance of self cells is known as immune tolerance
Autoimmune diseases are caused by the failure of immune tolerance
Result in activation of autoreactive T cells, and production of autoantibodies by B cells
Cause inflammation and organ damage
Alleviated by corticosteroids and NSAIDs, including aspirin 23 23