Immunity

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Immunity
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Body Defenses

• First line - barriers
• Skin and mucous membranes
• Flushing action
• Antimicrobial substances
• Lysozyme, acids, salts, normal microbiota
• Second line inflammation fever
• Both of these are non-specific

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• Third line immune response
• Specific
• Memory
• Inducibility

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• Antigens - substances recognized as non-self
  These can be
• Infectious agents - bacteria, viruses, fungi or
  parasites
• Noninfectious substances
• Environmental - pollen, foods, bee venoms
• Drugs, vaccines, transfusions and transplanted
  tissues

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Antigen

• Antibody Generator
• The best antigens are
• large
• recognized as foreign
• complex

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proteins and complex carbohydrates
good nucleic acids and lipids not good Haptens
too small by themselves, piggy-back on larger
molecules, us. Proteins Epitopes regions of
large molecules recognized by the immune system
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Two cell types give us the immune response both
are lymphocytes, which are a type of leukocyte,
or white blood cell. B lymphocytes or B cells T
lymphocytes or T cells
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The cells of the immune response differ from the
cells of the inflammatory response in three
ways 1. They are SPECIFIC and each cell
recognizes only one specific antigen. B cells
produce antibodies T cells attack antigen
directly
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2. Both produce groups of cells called memory
cells that act quickly the second time the
antigen is encountered. 3. An antigen induces
an immune response. Only small amounts of
antibodies or T Cells are present before
encountering an antigen.
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Long lasting protection against a specific
antigen is immunity. Natural immunity Not
produced by the immune response Species specific
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Acquired immunity Active person produces
immunity natural artificial Passive
temporary immunity is given natural artificial
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Lymphocytes
Originate in liver, spleen and bone marrow of
fetus in bone marrow after birth From stem
cells hemocytoblasts that produce all blood
cells.
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To become mature, immunocompetent cells, they
must pass through lymphoid tissues in other
parts of the body. As they do so, they become
committed to becoming either T cells or B
cells Cells that migrate through the bone marrow
become B cells, and will produce antigens and
participate in humoral immunity.
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Cells that migrate through the thymus glands
become T cells and participate in Cell-mediated
immunity
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Humoral Immunity
Humoral immune response B cells that produce
antibodies. Antibodies are proteins that match
the molecular structure of an antigen, and bind
to that antigen. This leads to the destruction of
the antigen.
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Antibody
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B cells mature in the human bursal equivalent
in bone marrow and obtain the ability to bind
antigens and produce antibodies. Clonal selection
theory During fetal development, B cells are
produced which can bind with any potential
antigen. Each B cell binds only one antigen.
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When antigen binds to antibody receptors on the
surface of the B cell, the B cell divides and
differentiates into antibody producing plasma
cells and also memory cells.
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Immunoglobulins

• IgG - monomer
• IgA dimer 2 units - in secretions
• IgM pentamer 5 units
• IgD monomer on surface of B cells
• IgE monomer involved in hypersensitivities
  

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Cell-mediated immunity

• Produced through Tcytoxic or Tc Cells (T8 cell)
• DO NOT produce antibodies
• Attack invaders directly
• May produce toxic chemicals such as perforins
• May stimulate cells self-destruct mechanism

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Primary and Secondary Immune Responses

• Primary response
• Latent period
• IgM produced
• IgG produced later

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• Secondary response
• Anamnestic response much more rapid due to
  memory cells
• Primarily IgG

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Cellular Interactions in the Immune Response

• Few antigens can activate B cells all by
  themselves
• For activation of B cells and Tc Cells need a
  second signal cytokine ( cell mover)

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Antigen-Presenting cells (macrophages) place
antigen on their cell surface in combination with
the MHC II complex Antigen is presented to a
specific helper T cell that has receptors that
match the antigen MHC II complex
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After binding, the APC produces Interleukin -1
(IL-1) which stimulates the TH Cell to produce
IL-2 and/or IL-4 Interleukin-2 has an autocrine
function, causes TH Cell to clone itself, and
make more IL-2 and /or IL-4
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Helper T cells

• TH1 cells produce IL -2 and influence
  cell-mediated immunity
• TH2 cells produce IL -4 (and other ILs) and
  influence antibody-mediated (humoral) immunity

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When B cell comes in contact with the antigen and
IL-4, the B cell produces plasma cells and memory
cells Tc Cells come in contact with the antigen
on the surface of infected cells in combination
with the MHC 1 complex. When also have binding
with IL-2, cells produce activated Tc Cells and
memory cells.
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