Download Chapter 43 Immune System

Chapter 43 Immune System
Innate Immunity
• This type of immunity is present before any exposure
to pathogens and begins at birth
• Largely nonspecific
• Skin is the first line of defense
• Mucous membranes that line the digestive, respiratory,
and genitourinary tracts
• Tears, sweat, and saliva are body secretions that serve
this type of immunity
• Lysozyme is an antimicrobial protein found in the skin
and mucous membrane that digests cell walls of
bacteria
Innate Immunity
• If microbes make it past the external defenses then
cellular and chemical defenses take over
• White blood cells that serve as phagocytes that engulf
and destroy microbes
- also initiate the inflammatory response
Four types of phagocytic WBC:
1. Neutrophils – most abundant; life span a few days
2. Macrophages – larger, longer living WBC, but only
5% in circulation; found in spleen, lymph nodes
3. Eosinophils – low activity, but essential to defend
against multicellular parasites
4. Dendritic cells – ingest much like macrophages
Phagocytosis
Innate Immunity
• Antimicrobial proteins directly attack proteins or
impede their reproduction
- complement system – 30 serum proteins that
are inactive without microbes
-trigger cascade of steps that lyse
invading cells; also trigger
inflammation
Interferon (alpha & beta) – proteins that defend
against viral infections
- secreted by virus infected cells to induce other
cells to produce substances to inhibit further
infection
Innate Immunity
• Inflammatory response – triggered from injury or entry of
pathogens to a site of body
- Mast cells found in connective tissue release
histamine
- release will trigger dilation and permeability of
capillaries
- increased blood flow causes redness and heat
- vascular changes deliver antimicrobial proteins and
clotting elements to site which begins repair and
blocks spread to other parts of body
- Chemokines – small proteins that direct the migration
of phagocytes and increase production of microbe
killing compounds
Inflammatory Reponse
Innate Immunity
• Fever is another systemic response in which
toxins from pathogen and substances from
macrophages set body’s temperature higher
• Natural Killer cells – nonspecific – patrol and
attack virus infected or cancer cells
- surface receptors recognize the target
and release chemicals that cause apoptosis
or programmed cell death
Summary
Acquired Immunity
• Develops only after exposure to inducing agents
and is highly specific
• Cytokines proteins secreted from macrophages
that activate the specific WBC called lymphocytes
• Antigen – any foreign molecule recognized by
lymphocytes and elicits a response
epitope – binding or recognition site on the
antigen that elicits a response
• Antibodies – defensive proteins released by
lymphocytes that recognize the epitope of
antigens and target them for destruction
Acquired Immunity
Two types of lymphocytes:
1. B Lymphocytes
2. T Lymphocytes
- Both use antigen specific receptors to recognize antigens
- B cells recognize intact antigens, whereas T cells can
recognize fragments of antigens
Acquired Immunity
• Major Histocompatibility Complex (MHC) –
family of genes that normal cell surface
proteins
- these proteins attach to antigens and present
them to the surface of the plasma membrane for
recognition by a particular T cell
- Class I MHC – found on almost all nucleated
cells of the body and recognized Cytotoxic T cells
- Class II MHC – made by dendritic, macrophages
and B cells and recognized by Helper T cells
Lymphocyte Development
• Both lymphocytes develop from pluripotent stem cells
- T cells – migrate to thymus, gland of thoracic
cavity, during maturation
- B cells – stay in bone marrow during maturation
(bursa of Fabricius)
Three key events of lymphocytes
1. maturation of B cell in marrow
2. maturation of T cell in thymus
3. Lymphocyte encounters and binds to antigens
leading to activation, proliferation, and
differentiation – clonal selection
Clonal Selection
• Clonal selection – antigen driven cloning of
lymphocytes that selectively activates tiny
fraction of cells that are specific for and
dedicated to eliminating that antigen
- effector cells – clone of large numbered short
lived cells that combat antigen
- memory cells – long lived cells bearing
receptors specific for same inducing antigen
Clonal Selection
• Primary immune response – proliferation and
differentiation of lymphocytes the first time
the body is exposed to antigen
- response peak in 10-17 days
• Secondary immune response – exposure to
the same antigen that produces a faster, more
prolonged response of greater magnitude
Acquired Immunity
• Two branches of immunity:
1. Humoral response – involves activation
and clonal selection of B cells that release
antibodies into blood and lymph
2. Cell-mediated response – activation and
clonal selection of cytotoxic T cells that
directly destroy target cells
Acquired Immunity
• Central to humoral and cell mediated
responses is the helper T cell
- CD4 is a surface protein on the helper T cell that
binds the class II MHC
- keeps helper T and antigen presenting cell
joined during activation of helper T clones and
memory cells
- leads to secretion of cytokines that stimulate
other lymphocytes
Acquired Immunity
• Cytotoxic T cells target virus infected cells and
cancer cells
- utilize CD8 surface protein that behaves
like CD4 in helper T cells
- Activated Cytotoxic T cells secrete
proteins that act on bound infected cell
and destroy it
- exposes pathogen to antibodies
Antibody Classes
• 5 classes
- binding sites are
responsible for
identification of
antigens
- tails are
responsible for
antibody
distribution and
mediation of
antigen disposal
Antibody Disposal
• 5 mechanisms of disposal by antibodies
1. Viral neutralization – binding of proteins to surface blocks
ability to infect host
2. Opsonization – bound antibodies enhance macrophage
attachment to microbes and increase phagocytosis
3. Agglutination – clumping of bacteria or viruses forms
aggregates that can be readily phagocytosed by macrophages
4. Precipitation – antibodies cross link soluble antigen
molecules dissolved in body fluids making them immobile and
easily targeted by phagocytes
5. Complement system – binding of antigen-antibody complex
causes complement proteins to activate a cascade of reactions
that generate a Membrane Attack complex (MAC)
*forms a pore in membrane, ions and water rush in and
cause cell to swell and lyse
Active & Passive Immunity
• Active immunity – occurs by natural exposure to
infectious agent
-can develop from immunizations or
vaccinations with inactivated form of bacterial
toxin, microbe, parts of microbe, genes of
microbial proteins
• Passive Immunity – conferred by transferring
antibodies from one immune individual to one
that has not been exposed to agent
Ex: mother passing antibodies to fetus
through colostrum
Blood Groups and Transfusions
• Blood types contain antigens that the body
recognizes as self and non-self
Ex: Type A blood with A antigens is
tolerant, but Type B blood will generate
antibodies and lead to a transfusion
reaction that can involves lyses of red
blood cells and can lead to chills, fever,
shock, and kidney malfunction
Blood Groups
• Rh factor – red blood cell antigen that triggers
antibodies (IgG) to mount a humoral response
on fetus
- Mothers can be injected with anti-Rh IgG
antibodies to prevent attack on future
fetuses
Allergies
• Allergies – exaggerated or hypersensitive responses to a
certain antigen or allergen
• Most common allergies involve IgE antibodies ( hay fever)
induction of mast cells cause release of histamine that
dialates blood vessels
- symptoms runny nose, sneezing, tearing eyes
Antihistamines block histamine receptors and diminish
allergy symptoms
Anaphylactic shock – whole body, life threatening reaction
with exposure to antigen
Ex: peanut allergies, bee stings
Autoimmune Disease
• Immune system loses tolerance of self and
turns against certain molecules of body
• - releases antibodies against self molecules
like histones and DNA
• - thought to arise from some failure of
immune system regulation