1. Immune System

2. Types of Immunity innate immunity acquired immunity
defenses present before exposure to pathogens
effective from birth
acquired immunity
defenses that develop after exposure to infectious agents & other foreign substances

3. Innate Immunity – External Defenses
intact skin
mucous membranes lining digestive, respiratory, & urinary tracts

4. Innate Immunity – Internal Defenses
phagocytes
cells that engulf microbes
4 types: neutrophils, macrophages, eosinophils, dendritic cells
antimicrobial proteins
enzymes that digest microbes
inflammatory response
see next slide

5. Inflammatory Response
when tissue becomes damaged, histamine is released which triggers the dilation & increased permeability of nearby capillaries
this promotes blood flow to the injured site which helps deliver antimicrobial proteins, clotting elements, & phagocytes to the injured area
as blood rushes to the injured area, it turns red & heats up
as fluid leaks out of the capillaries, the injured area swells

6. Acquired Immunity
acquired immunity is highly specific because lymphocytes (a type of white blood cell) are capable of recognizing different types of inducing agents (antigens)
antigens have specific binding sites called epitopes that lymphocytes (or the antibodies they secrete) recognize

7. Lymphocytes develop in bone marrow
if they mature in the bone marrow, they become B cells
if they migrate to the thymus to mature, they become T cells
elicit two general types of responses:
B cells secrete antibodies that circulate in the blood & lymph and bind to microbes, marking them for elimination (humoral response)
T cells are cytotoxic lymphocytes that directly target and destroy infected cells (cell-mediated response)

8. Lymphocyte Receptors
B cells have Y-shaped receptors with antigen-binding sites at the two tips of the “Y”
these binding sites recognize intact antigens that circulate in the body ( B cells target extracellular pathogens)
T cells have I-shaped receptors with one antigen-binding site
these binding sites recognize antigen fragments bound to surface proteins on infected cells ( T cells target intracellular pathogens)

9. Primary Immune Response
when an antigen binds to a lymphocyte, the lymphocyte is activated & gives rise to thousands of clones specifically targeted for that antigen (clonal selection)
some of these clones are short-lived (effector cells) & go straight to “battle”
others are long-lived (memory cells) & wait for future infections by the same antigen
the primary immune response peaks ~10-17 days after initial exposure to the antigen

10. Clonal Selection

11. Secondary Immune Response
when an individual is exposed to an antigen for a second time, the immune response is much faster (~2-7 days)
the number of antibodies produced is greater & they tend to have a greater affinity for the antigen

12. Helper T cells play a role in both humoral & cell-mediated responses
dendritic cells located in the epidermis & other tissues capture antigens and present them to helper T cells
activated helper T cells can then activate both B cells & cytotoxic T cells

13. Active vs. Passive Immunity
active immunity is conferred by:
natural exposure to an infectious agent
artificial exposure to an infectious agent via immunization (vaccination)
passive immunity is conferred by:
transferring antibodies from a person who is immune to a particular infectious agent to someone who is not
examples:
pregnant woman to fetus
mother to nursing infant
injection (artificial means)

14. When it all goes wrong…
Malfunctions of the immune system can produce effects ranging from the minor inconvenience of some allergies to the serious and often fatal consequences of certain autoimmune and immunodeficiency diseases.
Allergies are hypersensitive (exaggerated) responses to certain environmental antigens, called allergens.

15. Autoimmune Diseases
Sometimes the immune system loses tolerance for self and turns against certain molecules of the body, causing one of many autoimmune diseases.
In systemic lupus erythematosus (lupus), the immune system generates antibodies against all sorts of self molecules, including histamines.
Lupus is characterized by skin rashes, fever, arthritis, and kidney dysfunction.
Rheumatoid arthritis leads to damage and painful inflammation of the cartilage and bone of joints.

16. More Diseases…
In insulin-dependent diabetes mellitus, the insulin-producing beta cells of the pancreas are the targets of autoimmune cell-mediated responses.
Multiple sclerosis (MS) is the most common chronic neurological disease in developed countries,
In MS, T cells reactive against myelin infiltrate the central nervous system and destroy the myelin of neurons.
People with MS experience a number of serious neurological abnormalities.