1. Chapter 24
The Immune System

2. Immune System: Overview
Immunity is the body’s ability to protect itself against infectious disease
The immune system has three types of components
Lymphoid tissues
Various types of immune cells
Chemical signals that coordinate responses
The immune system is able to recognize molecules as foreign (“non-self”) and specifically attack them

3. Lymphatic System: Introduction
The lymphatic system is a vascular system that collects tissue fluid and returns it to the blood. This lymphatic fluid (called lymph) is monitored for pathogens by immune system cells as it travels.
(a)
Figure 24-2a

4. Immune System: Functions
Protects against pathogens
Bacteria
Viruses
Parasites
Protects against foreign molecules (e.g., toxins)
Removes dead or damaged cells
Attempts to recognize and remove abnormal cells

5. Pathogens: Bacteria and Viruses
Table 24-1

6. Body Defenses: Two Lines of Defense
Physical and chemical barriers
Skin, epithelial linings, and cilia
Acids, mucus, and lysozymes
Immune defenses
Innate immunity
Non-specific – responds to a range of signals
Immediate response
Acquired immunity
Specific – attacks a specific pathogen or antigen
Slower but stronger response
Memory allows for fast responses upon re-exposure

7. Leukocytes Mediate Immunity
Granulocytes
Eosinophils
Basophils and mast cells
Neutrophils
Agranulocytes
Monocytes and macrophages
Lymphocytes

8. Phagocytosis of Pathogens Without Capsules
Recognizing the pathogen
Phagocytosis of Pathogens Without Capsules
Phagocytosis of Pathogens With Capsules
Figure 24-6a

9. Antigen-Presenting Cells
Lysosome
Antigen
Membrane proteins
Nucleus
Macrophage
Macrophage digests antigen in lysosome.
Antigen-presenting macrophage displays antigen fragments on surface receptors.
Figure 24-5

10. Activation of T Lymphocytes1
Cell binds to T lymphocyte. 2
Signal transduction activates T lymphocyte.
MHC-antigen complex
T-cell receptor
T lymphocyte
MCH receptor
Figure 24-15

11. Each Lymphocyte Clone has a Unique Surface Receptor
All lymphocytes contain proteins on their cell surface capable of binding a foreign antigen
Lymphocytes that all bind a particular antigen are called a clone
A clone is a group of lymphocytes that are specific to one antigen.
Clone 1
Clone 2
Clone 3
Figure 24-9

12. Four Steps in an Immune Response
Detection and identification of the foreign substance
Communication with other immune cells
Recruitment of other immune cells, and coordination of the response
Destruction or suppression of the invader
Get in groups and use these general steps to draw a diagram describing ALL the steps we discussed in class. They are a total of 10 steps!!

13. Innate Immunity: Internal Non-specific Defenses
Phagocytes ingest foreign cells and chemicals
Macrophages
Neutrophils
Natural killer (NK) cells kill tumor cells and infected cells
Cytokines mediate the inflammatory response
Inflammation
Fever

14. NK Cells Kill Infected and Tumor Cells
NK cells induce apoptosis in infected cells
NK cells attack some tumor cells
NK cell secrete chemical signals called interferons
Interferon-alpha and interferon-beta
Prevent viral replication
Interferon-gamma
Activates macrophages and other immune cells

15. Inflammation
Infection or tissue damage stimulates a set of local nonspecific reactions called inflammation
Three beneficial roles of inflammation are to:
Attract immune cells and chemical mediators to sites of infection
Create physical barriers to prevent infections from spreading
Promote tissue repair

16. Steps in the Inflammatory Response
Chemical signals called cytokines are released upon tissue damage or infection
Acute-phase proteins help prevent tissue damage
Cytokines stimulate histamine release from mast cells
Histamine causes two local vascular changes:
vasodilation  leads to heat and redness
nearby capillaries become more permeable
2a - wbc’s and plasma proteins move into tissue
2b - edema (swelling) results from the osmotic effect of the plasma proteins

17. Immune Response Chemicals - Functional Classes
Table 24-2

18. Antibody Structure
Figure 24-12

19. Antibodies Antibodies are also known as gamma globulins
Five classes of antibodies vary in their Fc region
IgG - most common, secondary response is IgG
IgA - secretory form (saliva, tears, breast milk, etc.)
IgE - involved in allergic responses
IgM - antibodies involved in primary response
IgD - found on surface of B cells, role unclear

20. Functions of Antibodies
Figure 24-13

21. Major Histocompatibility Complex
Major histocompatibility complex (MHC) proteins help our immune system defend against intracellular pathogens and cancers
MHC class I proteins
Found on all nucleated cells of the body
Recognized by cytotoxic T cells
MHC class II proteins
Found only on antigen-presenting cells
Recognized by helper T cells

22. Allergic Responses
An allergy is an inflammatory response to a nonpathogenic antigen (called an allergen)
Immediate hypersensitivity reaction
Occur within minutes
Mediated by antibodies
Delayed hypersensitivity reaction
Occur after several days
Mediated by helper T cells and macrophages

23. Blood Types: ABO Blood Groups
No A or B antigens
Blood type
Antigen on red blood cell
Antibodies in plasma
“Anti-A” and “anti-B’”
“Anti-B”
“Anti-A”
None to A or B
A antigens
B antigens
A and B antigens O A B AB
(a)
(b) Mixture of Type A and O
Figure 24-20a

24. Immune System Pathologies - Can you explain them with your current knowledge?
Allergies
Autoimmune
Immuno-deficiency

25. Stress Alters Immune System Function
Nonspecific stimuli (“stressors”) disrupt homeostasis
Two types of stress elicit two types of response
Acute stress results in the fight-or-flight reaction
Chronic stress elevates cortisol levels, which suppresses immune responses
Figure 24-21