Download Immunology PPT - Old Saybrook Public Schools

The Basics of Immunology
The Immune System Simplified (?)
Immune System
• protects an organism against potential
pathogens (viral, bacterial, fungal, protists)
• consists of innate immunity and acquired
(adaptive) immunity
Innate Immunity
• nonspecific
• present all of the time or may be activated
• immediate
• all animals
Innate Immunity
Barriers:
skin - pH 3-5 acidic that prevents the growth of pathogens
secretions - saliva and tears have lysozyme
mucus membranes (produce defensins):
nasal, reproductive, digestive, respiratory, urinary
Cellular :
Leukocytes - phagocytic white blood cells
Neutrophils - most abundant, attracted to infected cells which are then engulfed
Macrophages - migrate throughout the body, others reside in tissues (lymph nodes, spleen)
Eosinophils - defend against multicellular parasites such as worms
Dendritic cells - populate tissues in contact with the environment
Natural Killer Cells (NK) - recognize cancer cells, those infected by viruses
Innate Immunity
Peptides and Proteins:
Interferons - produced by virus infected cells, limit cell-to-cell spread of viruses
Complement - 30 proteins in blood, circulate in inactive form but are activated by
substances on surface of pathogens, leads to lysis
Inflammation:
Mast cells release histamine, triggers permeability of blood vessels
Macrophages send out signals promoting blood flow to injured site, clotting
Antimicrobial peptides enter the tissue
Neutrophils and macrophages - phagocytosis of microbes
Pus accumulates (WBC, debris, dead microbes)
Acquired (Adaptive)
Immunity
• only in vertebrates
• specific
• diverse
• distinguishes self from nonself
• immunological memory
• slow
Acquired Immunity
Bone Marrow
(stem cells)
Lymphocytes (WBC)
Thymus
T cells
Thymus
all T cells produced as a child
thymus shrinks as an adult
B cells
Both B and T cells recognize and inactivate
foreign cells and molecules
Antigens/Antibodies
Antigens
1. any foreign substance(protein or
polysaccharide) that is recognized
by lymphocytes and elicits a
response from them
2. some are released from microbes
as toxins others protrude from
surface of pathogens
3. epitope is the region of an antigen
that an antibody recognizes
T cell receptors are antigen receptors
Antibodies
1. produced by B cells that have become
plasma cells
2. secreted soluble form of antigen receptor
(antibody or immunoglobulin)
3. antigen receptors on B cells
Antibodies
(Immunoglobulins Ig)
• tetramer - 4 polypeptide chains- 2 identical light chains, 2 identical heavy
chains
•
held together by a disulfide bond
•
each chain has a constant region and each has a variable region
•
constant region determines general structure and function, may insert into
membrane
•
variable region different for each specific Ig, 3-D antigen binding site due to
secondary structure, responsible for antibody specificity
5 Classes of Ig
• IgG - secreted by B cells (80% of circulating antibodies)
•
IgD - cell surface receptor on B cells, clonal
selection
•
IgM - first to be produced after antigen
exposure, promotes neutralization of antigens
•
IgA - present in secretions, saliva, tears,
mucus, breast milk(provides immunity to baby)
•
IgE - present in blood, triggers release of
histamine from mast cells, activates allergic
response
Major Histocompatibility Complex
(MHC)
genes that produce host cell protein receptors (HLA) capable of presenting
antigen fragments to a T cell
Human Leukocyte Antigens (HLA) vary from individual to individual,
important in transplantation
•
Class I MHC molecules - all cells except RBC,
cells infected can display antigens on the MHC
molecules to be recognized by immune system
cells (cytotoxic T cells)
•
Class II MHC molecules - made only by
antigen-presenting cells such as macrophages,
B cells, dendritic cells, display antigens after
cells have digested the foreign material,
recognition by helper T cells and cytotoxic T
cells
B Cells and T Cells
• lymphocytes
•
recognize and inactivate foreign cells and
molecules
•
contribute to immunological memory
• macrophages/dendritic cells ingest microbes
then secrete cytokines that activate
lymphocytes
B Cell and T Cell Receptors
• B cell receptor similar to antibodies but are membrane bound,
bind several antigens
• T cell receptors membrane bound but only bind to one antigen
• B cell receptors bind to an intact antigen that is free or on the
surface of a pathogen
• T cell receptors bind only to antigen fragments that are displayed
on the surface of host cells
Lymphocyte Diversity
• Humans respond to 10 million different antigens
• Each person has > 1 million different B cells and ~10 million
different T cells
• Recognition of an antigen precludes an immune system response
where lymphocytes with the right specificity to the antigen are
activated
• After T and B cells form, DNA rearrangements (mutations) occur
generating many diverse T cell receptors and antibodies
Cell Mediated Immune Response
T Helper Cells
1. respond to nearly all antigens
2. proliferates (mitosis) after encountering antigens or antigen-presenting
cells
3. clone of cells are now activated T helper cells and memory helper T cells
4. secrete cytokines that activate B cells
Killer T cells also
cytotoxic T cells
Humoral Immune Response
Clonal Selection
Amplification of B Cells
Primary Immune Response
1. peaks 10-17 days after initial exposure
2. B cells generate antibody secreting cells (plasma cells)
3. T cells are activated to T helper cells and cytotoxic T
cells
Secondary Immune Response
1. peaks 2-7 days after second exposure
2. reaction is stronger and prolonged
3. relies on T and B memory cells
4. rapid formation of effector cells (short lived, attack
antigen and any pathogen producing the antigen)