1. The Basics of Immunology
The Immune System Simplified (?)

2. Immune System
protects an organism against potential pathogens (viral, bacterial, fungal, protists)
consists of innate immunity and acquired (adaptive) immunity

3. Innate Immunity nonspecific
present all of the time or may be activated
immediate
all animals

4. Innate Immunity
Barriers:
skin - pH 3-5 acidic that prevents the growth of pathogens
secretions - saliva and tears have lysozyme
mucus membranes (produce defensins):
nasal, reproductive, digestive, respiratory, urinary
Cellular :
Leukocytes - phagocytic white blood cells
Neutrophils - most abundant, attracted to infected cells which are then engulfed
Macrophages - migrate throughout the body, others reside in tissues (lymph nodes, spleen)
Eosinophils - defend against multicellular parasites such as worms
Dendritic cells - populate tissues in contact with the environment
Natural Killer Cells (NK) - recognize cancer cells, those infected by viruses

5. Innate Immunity
Peptides and Proteins:
Interferons - produced by virus infected cells, limit cell-to-cell spread of viruses
Complement - 30 proteins in blood, circulate in inactive form but are activated by substances on surface of pathogens, leads to lysis
Inflammation:
Mast cells release histamine, triggers permeability of blood vessels
Macrophages send out signals promoting blood flow to injured site, clotting
Antimicrobial peptides enter the tissue
Neutrophils and macrophages - phagocytosis of microbes
Pus accumulates (WBC, debris, dead microbes)

6. Acquired (Adaptive) Immunity
only in vertebrates
specific
diverse
distinguishes self from nonself
immunological memory
slow

7. Acquired Immunity Bone Marrow B cells Lymphocytes (WBC) Thymus T cells
(stem cells)
Lymphocytes (WBC)
B cells
Thymus
Both B and T cells recognize and inactivate
foreign cells and molecules
T cells
Thymus
all T cells produced as a child
thymus shrinks as an adult

8. T cell receptors are antigen receptors
Antigens/Antibodies
Antigens
1. any foreign substance(protein or polysaccharide) that is recognized by lymphocytes and elicits a response from them
2. some are released from microbes as toxins others protrude from surface of pathogens
3. epitope is the region of an antigen that an antibody recognizes
Antibodies
1. produced by B cells that have become plasma cells
2. secreted soluble form of antigen receptor (antibody or immunoglobulin)
3. antigen receptors on B cells
T cell receptors are antigen receptors

9. Antibodies (Immunoglobulins Ig)
tetramer - 4 polypeptide chains- 2 identical light chains, 2 identical heavy chains
held together by a disulfide bond
each chain has a constant region and each has a variable region
constant region determines general structure and function, may insert into membrane
variable region different for each specific Ig, 3-D antigen binding site due to secondary structure, responsible for antibody specificity

10. 5 Classes of Ig
IgG - secreted by B cells (80% of circulating antibodies)
IgD - cell surface receptor on B cells, clonal selection
IgM - first to be produced after antigen exposure, promotes neutralization of antigens
IgA - present in secretions, saliva, tears, mucus, breast milk(provides immunity to baby)
IgE - present in blood, triggers release of histamine from mast cells, activates allergic response

11. Major Histocompatibility Complex (MHC) genes that produce host cell protein receptors (HLA) capable of presenting antigen fragments to a T cell Human Leukocyte Antigens (HLA) vary from individual to individual, important in transplantation
Class I MHC molecules - all cells except RBC, cells infected can display antigens on the MHC molecules to be recognized by immune system cells (cytotoxic T cells)
Class II MHC molecules - made only by antigen-presenting cells such as macrophages, B cells, dendritic cells, display antigens after cells have digested the foreign material, recognition by helper T cells and cytotoxic T cells

12. B Cells and T Cells lymphocytes
recognize and inactivate foreign cells and molecules
contribute to immunological memory
macrophages/dendritic cells ingest microbes then secrete cytokines that activate lymphocytes

13. B Cell and T Cell Receptors
B cell receptor similar to antibodies but are membrane bound, bind several antigens
T cell receptors membrane bound but only bind to one antigen
B cell receptors bind to an intact antigen that is free or on the surface of a pathogen
T cell receptors bind only to antigen fragments that are displayed on the surface of host cells

14. Lymphocyte Diversity Humans respond to 10 million different antigens
Each person has > 1 million different B cells and ~10 million different T cells
Recognition of an antigen precludes an immune system response where lymphocytes with the right specificity to the antigen are activated
After T and B cells form, DNA rearrangements (mutations) occur generating many diverse T cell receptors and antibodies

15. Cell Mediated Immune Response T Helper Cells
1. respond to nearly all antigens
2. proliferates (mitosis) after encountering antigens or antigen-presenting cells
3. clone of cells are now activated T helper cells and memory helper T cells
4. secrete cytokines that activate B cells
Killer T cells also
cytotoxic T cells

16. Humoral Immune Response Clonal Selection Amplification of B Cells

18. Primary Immune Response
1. peaks days after initial exposure
2. B cells generate antibody secreting cells (plasma cells)
3. T cells are activated to T helper cells and cytotoxic T cells
Secondary Immune Response
1. peaks 2-7 days after second exposure
2. reaction is stronger and prolonged
3. relies on T and B memory cells
4. rapid formation of effector cells (short lived, attack
antigen and any pathogen producing the antigen)