1. Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis.
Plants, invertebrates, and vertebrates have multiple, nonspecific immune responses

2. Pathogens (microorganisms and viruses)
Fig. 43-2
Pathogens
(microorganisms
and viruses)
INNATE IMMUNITY
Barrier defenses:
Skin
Mucous membranes
Secretions •
Recognition of traits
shared by broad ranges
of pathogens, using a
small set of receptors
Internal defenses:
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells •
Rapid response
Figure 43.2 Overview of animal immunity
ACQUIRED IMMUNITY
Humoral response:
Antibodies defend against
infection in body fluids. •
Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
Cell-mediated response:
Cytotoxic lymphocytes defend
against infection in body cells. •
Slower response

3. Innate Immunity
Innate immune responses are active immediately upon infection are the same whether or not the pathogen has been encountered previously
Innate immunity includes:
Barrier defenses such as skin, mucous membranes, & secretions
Internal defenses such as phagocytic cells, antimicrobrial proteins, inflammatory response & natural killer cells

4. Plants
Epidermis is a plants first line of defense (or periderm in woody plants)
If a pathogen successfully infects a plant cell, the plant can recognize invading pathogens and defend against them by chemical attack
Hypersensitive response – upon infection by some pathogens a signal transduction pathway triggers a programmed death to infected cells

5. Plants
Systemic Acquired Resistance: localized and specific; a containment response based on gene-for-gene recognition between host and pathogen
Methylsalicyclic acid is carried throughout the plant via the phloem; at the site of the infection it is converted to salicylic acid which activates signal transduction to produce proteins to resist pathogen attach

6. Invertebrates Only form of defense is Innate Immunity
Boundary defense:
Outer boundaries (i.e. exoskeleton or skin) 1st line of defense
Lysozyme – enzyme found in gut; digest microbial cell walls
Low pH – further protects digestive system
Internal defense:
phagocytic cells (hemocytes) engulf and destroy invaders
Secreting cells are triggered by signal transduction pathways to produce chemicals (including antimicrobial peptides) that kill, trap and/or inactivate microbes

7. Microbes PHAGOCYTIC CELL Vacuole Lysosome containing enzymes Fig. 43-3
Figure 43.3 Phagocytosis

8. Vertebrates Barrier Defenses: skin and mucous membranes block entry
Mucous traps microbes and cilia sweep it away
Saliva, tears and mucus: contain lysozyme to destroy and wash away microbes
Acidic environment of stomach, skin and sweat prevent growth of microbes

9. Vertebrates Cellular Defenses:
Toll-like receptors (TLR) – membrane receptors recognize components found in microbes; upon contact with microbe TLR trigger a series of internal defenses beginning with phagocytosis
Phagocytic cells include –
NEUTROPHILS - most abundant; engulf and destroy microbes
MACROPHAGES – “big eaters;” large cells that migrate through the body or permanently reside in certain organs; well positioned to fight microbes
ESINOPHILS – defend against multi-cellular invaders (i.e. parasitic worms) by releasing destructive chemicals
DENDRITIC cells - stimulate acquired immunity against invaders

10. Vertebrates Cellular Defenses Antimicrobial peptides and proteins
INTERFERONS – secreted by virus infected body cells inducing nearby uninfected cells to produce substances that inhibit viral reproduction (LIMIT CELL TO CELL SPREAD)
COMPLEMENT SYSTEM – roughly 30 proteins found in blood plasma; circulate in an inactive form; upon contact with microbes they become active; activation involves a series of actions that results in the lysis of the invading cells
NATURAL KILLER CELLS – target and destroy cells that have been infected; preventing spread of disease to healthy cells

11. Mast Cells – connective tissue cells that store chemicals for secretion
Histamine is released by mast cells at sites of damage triggers blood vessels to dilate and become permeable
Activated macrophages release more signaling molecules to further increase blood flow
Increased blood supply causes redness, heat & swelling
Antimicrobrial proteins , complement systems, phagocytes, etc… arrive via blood stream to destroy the invader which results in the accumulation of pus (fluid of WBC, dead microbes, & cell debris)
Vertebrates Inflammatory Response: changes brought about by signaling molecules released upon injury or infection

12. Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis.
Mammals use specific immune responses triggered by natural or artificial agents that disrupt dynamic homeostasis

13. Lymphocytes that mature in bone marrow are called B cells
Acquired Immunity
White blood cells called lymphocytes recognize and respond to antigens, foreign molecules
Lymphocytes that mature in the thymus above the heart are called T cells
Lymphocytes that mature in bone marrow are called B cells

14. Immune System
Tonsils and adenoids – protect by trapping germs that enter through your mouth and nose
Thymus – produces T-cells
Spleen – filters blood looking for foreign cells
Bone Marrow – produces new RBC and WBC from stem cells; where B-cells are formed
Appendix – may serve as a storehouse for “good” bacteria
Lymph – clear / white made of WBC – particularly lymphocytes
Lymph Nodes - found throughout the body help recognize and fight infections; contain B, T and other immune cells
Lymphatic vessels – mirror the blood stream so that it can send out immune cells when needed
Peyer’s Patches -oval elevated patches of closely packed lymph follicles on the mucosa of the small intestines.

15. B cells and T cells have receptor proteins that can bind to foreign molecules
Each individual lymphocyte is specialized to recognize a specific type of molecule
An antigen is any foreign molecule to which a lymphocyte responds
A single B cell or T cell has about 100,000 identical antigen receptors
Antigen Receptors All antigen receptors on a single lymphocyte recognize the same epitope, or antigenic determinant, on an antigen

16. B cell receptors bind to specific, intact antigens
The B cell receptor consists of two identical heavy chains and two identical light chains
The tips of the chains form a constant (C) region, and each chain contains a variable (V) region, so named because its amino acid sequence varies extensively from one B cell to another
B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins Secreted antibodies, or immunoglobulins, are structurally similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane

17. T cells bind to antigen fragments presented on a host cell
These antigen fragments are bound to cell-surface proteins called MHC molecules
MHC molecules are so named because they are encoded by a family of genes called the major histocompatibility complex
In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, a process called antigen presentation A nearby T cell can then detect the antigen fragment displayed on the cell’s surface

18. The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly
This proliferation of lymphocytes is called clonal selection
Two types of clones are produced: short-lived activated effector cells and long-lived memory cells
Clonal Selection

19. The first exposure to a specific antigen represents the primary immune response
During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms
In the secondary immune response, memory cells facilitate a faster, more efficient response
Second Exposure

20. Mammalian Immune System
Cell Mediated Response
Humoral Response
involves activation and clonal selection of cytotoxic T cells
Specific immunity brought about by T cells; fights body cells infected with pathogens; promotes phagocytosis by other white blood cells
involves activation and clonal selection of B cells, resulting in production of secreted antibodies
Specific immunity brought about by antibody producing B cells; fights bacteria and viruses in body fluids
Helper T cells aid both responses

21. Figure 43.16 An overview of the acquired immune response
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure) +
Stimulates
Gives rise to
Engulfed by
Antigen-
presenting cell + + +
B cell
Helper T cell
Cytotoxic T cell + +
Memory
Helper T cells + + +
Figure An overview of the acquired immune response
Antigen (2nd exposure) +
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Plasma cells
Memory B cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.

22. Helper T Cells
A surface protein called CD4 binds the class II MHC molecule
This binding keeps the helper T cell joined to the antigen- presenting cell while activation occurs
Activated helper T cells secrete cytokines that stimulate other lymphocytes

23. Killer T Cell
Cytotoxic T cells are the effector cells in cell- mediated immune response
Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell
Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer
The activated cytotoxic T cell secretes proteins that destroy the infected target cell

24. B Cells
The humoral response is characterized by secretion of antibodies by B cells
Activation of B cells is aided by cytokines and antigen binding to helper T cells
Clonal selection of B cells generates antibody-secreting plasma cells, the effector cells of humoral immunity

25. Neutralization occurs when a pathogen can no longer infect a host because it is bound to an antibody
Opsonization occurs when antibodies bound to antigens increase phagocytosis
Antibodies together with proteins of the complement system generate a membrane attack complex and cell lysis
Antibodies: The five major classes of antibodies, or immunoglobulins, differ in distribution and function

26. Vaccines