Transcript Groups of adhesive molecules

CYTOKINES,
SURFACE MOLECULES,
ANTIBODIES
Jan Novák
The Immune System is the Third Line of
Defense Against Infection
Clonal Selection of B Cells is Caused by
Antigenic Stimulation
•
Humoral Immunity - apoptosis
 Programmed
cell death (“Falling away”).
 Human body makes 100 million lymphocytes
every day. If an equivalent number doesn’t die,
will develop leukemia.
 B cells that do not encounter stimulating
antigen will self-destruct and send signals to
phagocytes to dispose of their remains.
 Many virus infected cells will undergo
apoptosis, to help prevent spread of the
infection.
Immunological Memory
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Antibody Titer: The amount of antibody in the
serum.
– Pattern of Antibody Levels During Infection
– Primary Response:
 After initial exposure to antigen, no antibodies
are found in serum for several days.
 A gradual increase in titer, first of IgM and then
of IgG is observed.
 Most B cells become plasma cells, but some B
cells become long living memory cells.
 Gradual decline of antibodies follows.
–
•Antibody

Monomer: A flexible Y-shaped molecule with four protein
chains:
2 identical light chains
 2 identical heavy chains
Variable Regions: Two sections at the end of Y’s arms.
Contain the antigen binding sites (Fab). Identical on the
same antibody, but vary from one antibody to another.
Constant Regions: Stem of monomer and lower parts of Y
arms.
Fc region: Stem of monomer only. Important because they
can bind to complement or cells.
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Structure
Antibodies are Proteins that Recognize
Specific Antigens
Consequences of AntigenAntibody Binding
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–
1. Agglutination: Antibodies cause antigens
(microbes) to clump together.
IgM (decavalent) is more effective that IgG (bivalent).
 Hemagglutination: Agglutination of red blood cells.
Used to determine ABO blood types and to detect
influenza and measles viruses.

2. Opsonization: Antigen (microbe) is covered
with antibodies that enhances its ingestion and
lysis by phagocytic cells.
Humoral Immunity
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3. Neutralization: IgG inactivates viruses by
binding to their surface and neutralize
toxins by blocking their active sites.
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4. Antibody-dependent cell-mediated
cytotoxicity: Used to destroy large organisms
(e.g.: worms). Target organism is coated with
antibodies and bombarded with chemicals from
nonspecific immune cells.
5. Complement Activation: Both IgG and IgM
trigger the complement system which results in
cell lysis and inflammation.
Consequences of Antibody Binding
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Immunoglobulin Classes
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I. IgG
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Structure: Monomer
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Percentage serum antibodies: 80%

Location: Blood, lymph, intestine

Half-life in serum: 23 days

Complement Fixation: Yes

Placental Transfer: Yes
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Known Functions: Enhances phagocytosis, neutralizes
toxins and viruses, protects fetus and newborn.
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Immunoglobulin Classes
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II. IgM
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Structure: Pentamer
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Percentage serum antibodies: 5-10%

Location: Blood, lymph, B cell surface (monomer)

Half-life in serum: 5 days

Complement Fixation: Yes

Placental Transfer: No

Known Functions: First antibodies produced during an
infection. Effective against microbes and agglutinating
antigens.
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Immunoglobulin Classes
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III. IgA

Structure: Dimer

Percentage serum antibodies: 10-15%

Location: Secretions (tears, saliva, intestine, milk), blood and
lymph.

Half-life in serum: 6 days

Complement Fixation: No

Placental Transfer: No

Known Functions: Localized protection of mucosal surfaces.
Provides immunity to infant digestive tract.
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Immunoglobulin Classes
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IV. IgD
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Structure: Monomer
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Percentage serum antibodies: 0.2%
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Location: B-cell surface, blood, and lymph

Half-life in serum: 3 days
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Complement Fixation: No
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Placental Transfer: No
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Known Functions: In serum function is unknown. On B cell
surface, initiate immune response.
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Immunoglobulin Classes
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V. IgE
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Structure: Monomer
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Percentage serum antibodies: 0.002%
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Location: Bound to mast cells and basophils throughout
body. Blood.
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Half-life in serum: 2 days
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Complement Fixation: No
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Placental Transfer: No
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Known Functions: Allergic reactions. Possibly lysis of
worms.
CYTOKINES
a diverse group of non-antibody proteins
released by cells that act as intercellular
mediators, especially in immune processes
CYTOKINES
Low molecular weight soluble proteins (polypeptides)
produced in response to microbes and other antigens
They act via cell surface receptors to mediate and regulate
the amplitude and duration of the immune-inflammatory
responses, through activation of macrophages,
controlling growth and differentiation of T and B cells
Naming of Cytokines
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1. Monokines - produced by mononuclear
phagocytes (monocytes)
2. Lymphokines - produced by activated T
cells, primarily helper T cells
3. Interleukins - cytokines made by one
leukocyte and acting on other leukocytes
4.Chemokines-cytokines with chemotactic
activities
Classification of Cytokines
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Interleukins - cytokines made by one leukocyte and
acting on other leukocytes
Chemokines - cytokines with chemotactic activities
Interferons – tissue antiviral cytokines
Transforming growth factors – growth, regulation
Colony stimulating factors – growth, stimulation
Tumor necrosis factors – induction of apoptosis
Properties
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1.Produced by cells involved in both natural and specific
immunity
2. Mediate and regulate immune and inflammatory
responses
3. Secretion is brief and limited not stored as pre-formed
molecules. Synthesis is initiated by new short-lived gene
transcription mRNA is short-lived
5. Redundancy -similar functions can be stimulated by
different cytokines.
Receptors for cytokines are heterodimers (sometimes heterotrimers)
that can be grouped into families in which one subunit is common
to all members of a given family. (hard clinical diagnostics)
Properties
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6. Often influence the synthesis of other cytokines. They can produce
cascades, or enhance or suppress production of other cytokines.
They exert positive or negative regulatory
mechanisms for
immune inflammatory responses
7. Often influence the action of other cytokines.
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antagonistic -cytokines causing opposing activities
additive
synergistic -two or more cytokines acting together (greater than
additive)
Properties
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8. Bind to specific receptors on target cells with high affinity..
9. Cellular responses to cytokines are generally slow (hours),
require new mRNA and protein synthesis
Cytokine action can be
Functional Categories of
Cytokines
1) Proinflammatory cytokines
- Produced by activated microphages and NK cells
in response to microbial infection
- chemotaxis
- killing
- IL1, IL-6, IL-8, IL-12, IL-18, TNF-a
Functional Categories of
Cytokines
2) Anti-inflammatory cytokines
- Produced mainly by T cells
- IL1Ra, IL-4, IL-10, TGF-b
Functional Categories of
Cytokines
3) Growth factors
- IL2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-11, IL-14, IL-15, G-CSF,
EPO…
Functional Categories of
Cytokines
4) Cytokines of humoral immunity
- IL-4, IL-5, IL-9, IL-13
Functional Categories of
Cytokines
5) Cytokines of cellular immunity
- IL-2, IL-12, IFN-g
Functional Categories of
Cytokines
6) Cytokines with antiviral potential
- IFN-a,b,g,
Cytokine Receptors
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Divided into several families based on their
structure and activities
Hematopoietin family
 receptors are dimers or trimers
 conserved cysteines in their extracellular
domains and a conserved Trp-Ser-X-Trp-Ser
sequence.
 Examples are receptors for IL-2 through IL-7
and GM-CSF.
Interferon family
 receptors have the conserved cysteine
residues but not the Trp-Ser-X-Trp-Ser
sequence,
 Eg. the receptors for IFNa, IFNb, and IFNg.
Tumor Necrosis Factor family
 receptors have four extracellular domains;
they include receptors for soluble TNFa and
TNFb as well as membrane-bound CD40
(important for B cell and macrophage
activation) and Fas (which signals the cell to
undergo apoptosis).
Chemokine family
 receptors have seven transmembrane helices
and interact with G protein. This family
includes receptors for IL-8, MIP-1 and
RANTES.
 Chemokine receptors CCR5 and CXCR4 are
used by HIV to preferentially enter either
macrophages or T cells.
Therapeutic Uses of Cytokines
1) Interferon in treatment of viral diseases, cancer
2) Several cytokines are used to enhance T-cell activation in
immunofideficincy diseases, e.g. IL-2, IFN-,TNF-
3) IL-2 and lymphokine activating killer cells (LAK) in treatment of
cancer
4) GM-CSF induces increase in white cell count, it is used:
a- To restore leukocytic count after cytotoxic
chemotherapy induced neutropenia
b- After bon marrow transplantation
C- To correct AIDS-associated leukopenia
5) Anti-cytokines antibodies in management of
autoimmune diseases and transplant rejection:
a- Anti-TNF in treatment rheumatoid arthritis
b- Anti-IL2R to reduce graft rejection
c- Anti-TNF antibodies in treating septic shock
d- Anti-IL-2R  in treating adult T-cell leukemia
e- Anti-IL-4 is under trial for treatment of
allergies
Adhesive molecules
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Adhesion of cells
Signal transduction
Groups of adhesive molecules
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Integrins
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Structures of intercellular matrix
Formed by two subunites (a and b)
Quiscent and activated conformation
LFA-1, VLA-1-5, CR3, CR4
Groups of adhesive molecules
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Molecules of immunoglobulin structure
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ICAM, CD80/86, CD2
Groups of adhesive molecules
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Selectins and Lectins
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L (leucotytes)
E (endothelial)
P (platelet)
Interactions between leukocytes and endothelium
Receptors of NK cells (Lektins of C type)
Groups of adhesive molecules
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Mucins
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CD43
Supression of interlekcocyte contact
FC receptors
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Bind FC parts of immunoglobulins
Divided according to the class of antibody
they bind
CD16, CD32, CD64
Complement receptors
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Phagocytosis of opsonized particles (CR3,4)
Clearance of immunocomplexes
Receptors for chemotaxis (C3aR, C5aR)
CD – cluster of differentiation
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system was intended for the classification of
the many monoclonal antibodies generated
by different laboratories around the world
against epitopes on the surface molecules
of leukocytes
proposed surface molecule is assigned a CD
number once two specific monoclonal
antibodies are shown to bind to the molecule
+/- or hi, mid or low
(alternatively bright, mid or dim
CD – cluster of differentiation
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CD1, CD2, CD3, CD4, CD5, CD8, CD11,
CD14, CD16, CD19, CD20, CD25, CD28,
CD34, CD38, CD45, CD56, CD69, CD96,
CD161