CAS PS 332 Lecture Notes - Lecture 6: Innate Immune System, Phagosome, Adaptive Immune System

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Published on 22 May 2019
Professor
Lecture 6: 2/7/19
Review of last class
The Immune System
o Acute stressors are protective, chronic stress increases your likelihood of
getting sick
o Two main functions:
Protect from foreign invasion by antigens (bacteria, viruses, fungi)
Remove damaged or mutant cells (cancer cells)
Overview:
o Lymphatic system: spread throughout body (capillaries, lymph nodes,
bone marrow, thymus, spleen, tonsils, etc)
o Acts throughout entire body
Leukocytes white blood cells
Lymphocytes, monocytes, eisonophils, basophils,
neutrophils
Lymph circulates through the blood and body
o Fluid of water, proteins, microbes, & foreign substances
Periodically enters lymph nodes
o Filters :Remove cellular debris, bacteria, etc.
o “Meeting space” for different types of immune cells
Physical barriers
o E.g. skin & mucous membranes (digestive, respiratory, & reproductive
tracts)
Innate immune system (“Nonspecific”)
o Available from birth
o Fast, non-specific response
Acquired immune system (“Specific”)
o Develops ~1 week after birth
o Developed to fight viruses (relatively new threat)
o Slower, specific response
Innate Immune System
Nonspecific immunity, second line of defense
Macrophage: defender cell that is programmed to recognize common antigens
o Attracted to chemicals released by antigens
o Travels to site of antigen
o Reaches out and “grabs” antigen- phagocytosis
“Big eater”
Phagocytosis
o Macrophage engulfs bacterium in a pouch, called a phagosome
o Phagosome taken into the macrophage
o Phagosome fuses with a lysosome
o Lysosome has chemicals that kill bacterium
During phagocytosis, macrophages give off chemicals that signal there is an
invader E.g., histamine
Cytokines: hormone like messengers that facilitate communication among
immune cells
o Coordinate inflammatory response
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Signals to immune cells that there is an invader
Other immune cells exit the blood vessels near antigen to restore
damaged tissue
Local and systemic effects
Inflammation, redness, heat
Natural Killer (NK) Cells
o Leave the blood & enter tissue at site of infection
o Function: Kill cells infected with viruses, bacteria, parasites, fungi, and
tumor cells Inject lethal enzymes into cell (perforin)
o Bind with proteins on the cell surface sends signal for cell to kill itself
(fragmentins)
o Also secrete cytokines E.g., Interferons inhibits the spread of viral
infections
o NK cells can distinguish normal vs. cancer cells
Communication between Innate and Acquired
o Cytokines
o Macrophages act as antigen-presenting cells (APCs)
Display fragments of antigens
“Seen” by T-cells (acquired immunity)
o Cytokines and inflammation are impacted by stress
Acquired Immunity
For antigens that elude/overwhelm nonspecific defenses
Acquired Immune System (Specific Immunity)
o 3rd line of defense
o 99% of animals don’t have this
o Past experience with a disease (e.g., measles), immunization, breast milk
creates a “memory”
Primary cell types: B- and T-Cells
o B cells - White blood cells that attack antigens by producing specific
antibodies
o T cells - White blood cells that attack antigens directly, without producing
antibodies; mature in thymus
o Begin as pluripotent stem cells in the bone marrow
o Mature in bone marrow (B) or move to thymus (T)
T-Cells: Differentiate into T-helper, T-cytotoxic, and T-regulatory
cells
B-Cells make antibodies (a.k.a. immunoglobulins) proteins that protect the
body against specific antigens
o B-Cell senses cognate antigen (specific one its designed to fight
against) -> proliferates into ~20,000 clones
Plasma vs. memory cells
Takes 1-2 weeks to complete
Clones produce antibodies specific to cognate antigen
Primary vs. secondary responses
o Primary: encounters cognate antigen and proliferates, creates memory
cells and clone plasma cells
Secondary: subsequent encounters with antigen cause memory cells to
attack and divide to produce new plasma and memory cells
Antibodies
o Antibodies have hand regions (fab regions), and tail region (Fc region)
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