1. Ch 43- Immune system

2. Immune system Defends body against disease
Pathogens – agents of disease (bacteria, viruses, protists)
Non specific immunity (innate immunity)
All animals & plants have defenses effective immediately upon infection
Specific immunity
(adaptive or acquired immunity)
All vertebrates have immunity after exposure to pathogens (slower response).

3. 1. Non-specific Immunity
1st line of defense: barrier
Skin, mucous membrane, secretions
2nd line of defense: internal defenses
Phagocytosis, natural killer cells, antimicrobial proteins, inflammatory response

4. Invertebrate defenses
1st barrier – exoskeleton made of chitin
Digestive system is protected by a chitin-based barrier and lysozyme, an enzyme that breaks down bacterial cell walls
The immune system recognizes bacteria and fungi by structures on their cell walls

5. Pathogen
PHAGOCYTIC CELL
Vacuole
Lysosome containing enzymes
Hemocytes
- circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria
- also secrete antimicrobial peptides that disrupt the plasma membranes of fungi and bacteria

6. Non-specific immunity in Vertebrates
Include barrier defenses, phagocytosis, antimicrobial peptides
Unique to vertebrates: natural killer cells, interferons, inflammatory response

7. Barrier defenses Skin Mucous membranes
Body secretions: saliva ,mucus, tears
Low pH in skin & membranes

8. Phagocytosis
“cell eating” – white blood cells ingest invading pathogens
Neutrophils – short lived white blood cells
Macrophages – largest phagocytes (from monocytes)
Engulfs microbe & fuses with lysosyme to destroy it
Found fixed in parts of lymphatic system (spleen, lymph nodes, thymus)
Some travel throughout body
Eosinophils – attack larger parasites

9. This increases efficiency of phagocytes
Phagocytes recognize groups of pathogens with Toll-like receptors (TLRs) that recognize molecular patterns characteristic of certain pathogens
This increases efficiency of phagocytes
i.e. double stranded RNA (in viruses)
Flagellin – protein found in bacteria flagella

10. Natural killer cells
Destroy virus-infected body cells
Attack cells membrane, so cell lyses
Lymphatic system involved in cellular non-specific defense
Lymph nodes hold many macrophages

11. Thymus
Adenoid
Tonsils
Lymphatic vessels
Spleen
Lymph nodes
Lymph node
Blood capillary
Interstitial fluid
Tissue cells
Lymphatic vessel
Masses of defensive cells

12. Antimicrobial proteins
Proteins involved in attacking microbes or stopping their reproduction
Lysozyme- present in tears & saliva, mucous
Complement proteins – 20 serum proteins – carry out steps to lyse microbes
Interferons – secreted by virus-infected cells, induce neighboring cells to produce chemicals to inhibit viral reproduction

13. Inflammatory response
Response to cut or entry of microorganisms
Area becomes inflamed, red, swollen
Result of chemical signals-
From invader
Nearby mast cells release histamines – released by body cells in response to injury
Histamines dilate capillaries and increase permeability, so fluid & clotting elements leave can enter site

14. Inflammatory response
Pathogen
Splinter
Mast cell
Macro- phage
Capillary
Red blood cells
Neutrophil
Signaling molecules
Movement of fluid
Phagocytosis

15. Clotting begins
Other cells release chemokines, which attract phagocytes to area
Phagocytes consume pathogens & debris
Pus - a fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues

16. 2. Specific Immunity
Specific immune responses to particular microorganisms
Found in vertebrates
Lymphocytes – type of white blood cells
2 types:
T cells – mature in thymus
B cells – mature in bone marrow

17. Antigens Substances that can elicit a response from a B or T cell
B or T cells have antigen receptors specific for parts of that pathogen – so they can recognize specific antigens
Antigen receptors
Mature B cell
Mature T cell

18. Recognizing antigens

20. The specificity of the T & B receptors (and antibodies) is a result of shuffling and recombining several gene segments to produce the protein
There are more than 1 million different B cells and 10 million different T cells
Due to random arrangment, some receptors are specific for epitopes on organism’s own molecules, so B & T cells must be tested for self- reactivity.

22. B cells:
Mature in bone marrow
Produce antibodies
Receptors bind to intact antigens
T cells:
Mature in thymus
Do not produce antibodies
Receptors bind to antigens displayed by antigen-presenting cells (APCs) on their MHCs
Both:
Activated by cytokines, from helper T cells

23. MHC – major histocompatability complex – cell surface glycoproteins that differ among individuals
- aid in recognition of “self”
- Class I – found on nearly all body cells
- can present fragments of proteins made by infecting microbes to cytotoxic T cells
- Class II – made by some cells of immune system
- macrophages & B cells
- molecules collect remnants of microbes and present them to helper T cells

24. Clonal selection Activation occurs when antigen binds to B or T cell.
Clones formed in clonal selection – two types produced:
Effector cells – fight the antigen
Memory cells – have receptors for same antigen, so allow quick response to subsequent infection

25. Responses
Primary response- when body first exposed to antigen and lymphocyte is activated
Secondary response – when same antigen is encountered later, faster more efficient response due to memory cells

26. Antibody concentration (arbitrary units)
Primary immune response to antigen A produces antibodies to A.
Secondary immune response to antigen A produces antibodies to A; primary immune response to antigen B produces antibodies to B.
Exposure to antigen A
Exposure to antigens A and B
Time (days)
Antibody concentration (arbitrary units)
104
103
102
101
100 7 14 21 28 35 42 49 56
Antibodies to A
Antibodies to B

27. Cell- mediated immunity
Activation & clonal selection of cytotoxic T- cells
Macrophages engulf antigens, process them internally, then display parts of them on their surface together with some of their own proteins. This sensitizes the T cells to recognize these antigens.

28. T-cells are trained in thymus
T- cells are chosen that have correct receptors to recognize MHC molecules
T- cells that can recognize MHC molecules complexed with foreign peptide are allowed to pass out of thymus

29. Cytotoxic T cells (Killer T cells) bind to class 1 MHC molecules, display fragments on surface of body cells. Destroy infected cells.
Helper T-cells: secrete cytokines in response to interaction with class 2 MHC molecules – stimulate & activate both cytotoxic T cells & B cells
Memory T cells – recognize & respond to antigen once it has already been encountered.

30. Humoral response Activation & clonal selection of effector B cells
Fight pathogens in body fluids
Activated B cells produce plasma & memory cells
Plasma cells –(effector cells) produce antibodies
Memory cells – for secondary response

31. Antibodies destroy antigens through:
Antibodies – soluble proteins secreted by B cells during an immune response
Antibodies destroy antigens through:
Neutralization: bind & block activity of antigen
Lysis: caused by activation of complement system- form a hole in membrane of pathogen
Agglutination: clumping of bacteria or viruses
Opsonization: results in increased phagocytosis of antigen (attracts macrophages)

32. Humoral response:
Specific immunity

33. Active immunity – when body is exposed directly to pathogen, body responds
(infection, vaccination)
Passive immunity – when an individual receives antibodies
(to fetus from mother across placenta)

34. Allergy reaction animation