Immunology Flashcards
Phagocytosis
ingestion and killing of micro-organisms by specialized cells
innate immunity
Polymorphonuclear Leukocytes
neutrophils, basophils, eosinophils
indicator of infection
innate immunity
Mononuclear Phagocytes
monocyte derived cells -> macrophages and dendritic cells
innate immunity
Toll-like receptors
family of receptors expressed on selected leukocytes
trigger inflammation
recognize molecular patterns
innate immunity
Lipopolysaccharides
component of gram negative bacteria cell wall
innate immunity
Humoral Immunity
B cells; antibodies
adaptive immunity
Cell-mediated immunity
T cell; terminators
adaptive immunity
Cytotoxicity
1 cell killing another cell
Innate immunity
ability to resist infection
not pathogen-specific
present from birth
no obvious enhancement by subsequent exposure
no specific memory
poorly effective without adaptive immunity
mediated largely by monocyte-derived cells and PMNs
Adaptive immunity
ability to adapt to infection
confers pathogen-specific immunity
continues to mature after birth; influenced by environment
enhanced by subsequent exposure
develop long term, specific memory
poorly effective without innate immunity
mediated by lymphocytes and monocyte-derived cells
Does protective immunity require both innate and adaptive immunity?
Yes
Why is there a lag time in developing adaptive immune responses?
dendritic cells select lymphocytes to activate and proliferate
immune system
body wide network of cells and organs for defending the body against attacks by foreign invaders
danger model
immune responses depend on context of how the antigen is presented
context is the degree of inflammation
antigen
any molecular entities capable of triggering adaptive immune responses
most often proteins
immunological specificity
cells of immune system respond to the molecular structure of an antigen
epitope
sub-structure of an antigen to which lymphocytes respond and remember
an antigen can have many of these
immunological versaitility
immune system ability to differentiate antigens and produces specific and appropriate response
immunological memory
response to a second exposure of the same antigen is faster and stronger than the response to the initial exposure
remains for years/decades
immunological tolerance
ability of the immune system to respond to foreign cells and compounds, but to generally ignore normal tissues and cells
has to be continuously maintained
can be central/peripheral
lymphatic system
cells in lymph nodes, spleen, bone marrow, lymphatic vessels, and tissues
polymorphonuclear granulocytes
have segmented nuclei and cell-specific cytoplasmic granules
includes neutrophils, eosinophils, basophils
neutrophils
number in the blood increases during infection
think bacteria
eosinophils
respond to allergic reactions
think asthma and parasites
basophils
respond to allergic reactions with histamine and heparin
think parasites
Lymphoid organs
thymus
spleen
bone marrow
lymph vessels and nodes
extends to skin and mucosal tissues
What is conveyed through the lymphatics in the lymph?
Immune cells and foreign particles
Where do T-cells go before they go to the lymph node?
the Thymus
Where is the thymus located?
Between the sternum and the aortic arch
How does the thymus prevent autoimmunity?
induces apoptosis of auto-reactive T cells
immature T cells are generated in bone marrow through?
random recombination of genes
B cells
produce antigen specific antibodies when activated
each is defined by its epitope specific receptor
T cells
regulate, help, and kill in antigen specific manner
each is define by its epitope specific receptor
What does each T and B cell clone express?
unique receptor that defines the cell’s antigen specificity
What are antigen presenting cells?
macrophages/dendritic cells/b lymphocytes
remove debris and defend against pathogens that cannot be dealt with by neutrophils
Cytotoxic T Cells
killers of virus and bacteria
Helper T Cells
directs T lymphocyte process
Regulatory T Cells
help with t lymphocyte peripheral tolerance
B lymphocytes
plasma cells cannot revert back to B cells
What are the three types of lymphocytes
T lymphocytes
B lymphocytes
natural killer cells
What is signal 1 in antigen presentation?
MHC-TCR antigen recognition
defines specificity of the immune response
What is signal 2 in antigen presentation?
costimulation (inflammation)
dictates intensity of the immune response
Activation of T cells by APC is xxx dependent?
Contact
An MHC bound peptide is an epitope if ?
it is recognized by T cells
What does MHC stand for?
major histocompatibility complex
human leukocyte antigens
MHC Class 1?
HLA-A, HLA-B, HLA-C
these engage cytotoxic T cells
expressed in all nucleated cells
MHC Class 2?
HLA-D
engage helper T-cells
expressed mostly by APCs
MHC genes are highly ?
polymorphic
several hundred alleles have been identified in humans
How many HLA alleles can a person express?
12
What is the probability of two individuals expressing the same set of MHC molecules?
very low
Where are MHC found?
mostly nucleated cells, APCs
What does MHC bind to ?
peptides
MHC 1 presents peptides to?
Cytotoxic T cells
MHC 2 presents peptides to ?
helper T cells
Where do peptides presented by MHC I come from?
proteins synthesized within cells
Where are peptides presented by MHC 2 derived from?
proteins internalized through phagocytosis
What are the steps in cell-mediated immunity?
Th and CTL recognize epitopes in MHC molecules and make clones
cell-cell contact attack, apoptosis of target cells
memory: most clones die when infections resolves but encounters generate long-lived memory T cells
Helper T cells express which molecule?
CD4
What do helper T cells respond to?
Class 2 MHC molecules
Which molecule do cytotoxic T cells express?
CD8
What do cytotoxic T cells respond to?
Class 1 MHC molecules
B7-CD28
this is on T lymphocytes
the antigen is captured, there is rapid expression of B7 on APC to provide the second signal of antigen presentation
What is a distinguishing feature of APC?
costimulation
What do perforin and granzyme do?
poke holes and inject enzyme that initiate apoptosis
cytokines
diverse and potent chemical messengers that bind specific receptors on target cells, recruit other cells, encourage cell growth, direct cellular traffic, and destroy target cells
What is the main source of interleukin—2?
Activated CD4 helper T cells
What is required for proliferation of lymphocytes?
interleukin-2
B cells
secrete antibodies, make antibodies that bind to a specific epitope, gives rise to plasma cells
What do B cells express?
BCR
MHC2
costimulatory molecules
IL-2 receptor
MHC1
A BCR will bind to an intact antigen through endocytosis and then combine with a class 2 MHC. What is this combination recognized by?
CD4 T helper cells
The binding of the antigen, MHC, and CD4 T helper cell activates what?
The t cell, which releases IL-2 that transforms B cell into plasma cells
Antibodies are also known as?
Immunoglobulins
What is the configuration of antibodies?
2 identical heavy chains
2 identical light chains
What do antibodies do?
neutralize and tag antigens for destruction
What is FAB or variable region on antibodies?
antigen binding fragment
recognizes a specific epitope
How many Fabs does each antibody have?
2
The constant region on antibodies is also called?
The Fc region
this mediates the killing mechanism
IgG
major immunoglobulin in the blood is able to enter tissue spaces
G stands for gamma
half life is 21 days in blood
IgD
almost exclusively found inserted into the membrane of B cells, where it regulates the cell’s activation
D stands for delta
BCR
IgE
normally present in only trace amounts
responsible for the symptoms of allergy (mast cell -> histamine)
IgA
doublet
concentrates in body fluids such as tears, saliva, and the secretions of the respiratory and gastrointestinal tracts
IgM
star shaped clusters
initial response to antigens
Humoral Immunity
- B cells recognize an antigen and divide repeatedly
- Plasma cells release antibodies that bind to the antigen, render it harmless, and tag it for destruction by other agents
- Some B cells differentiate into memory cells which provide lasting protection against future exposures to the same pathogen
Where are Fc receptors expressed? What do they do?
on select leukocytes
ex. neutrophils
capture antibody-bound antigens
Opsonization
internalization of antibody-tagged antigens
mediated through Fc portion of antibodies
