BIOL 1107 Chapter Notes - Chapter 48.2-48.5: Adaptive Immune System, Lymph Node, Antigen Presentation
Chapter 48.2 Adaptive Immunity: Recognition
● Leukocytes involved in the ability to recognize specific antigens and to differentiate
between species and even different strains of pathogens can customize their response
to particular invades. This is called the adaptive immune response.
● Antibodies are secreted proteins that bind to a specific part of a specific antigen.
- The adaptive immune system can recognize and respond to a seemingly limitless array
of antigens.
● There are four key characteristics of the adaptive immune system:
1. Specificity: Antibodies and other components of the adaptive immune system bind only
to specific sites on specific antigens.
2. Diversity: The adaptive immune system can recognize and respond to virtually any type
of antigen.
3. Memory: Adaptive immune responses are stronger and quicker when an individual is
exposed to antigens from previous infections.
4. Self-Nonself Recognition: Molecules that are produced by the individual do not normally
trigger a response, meaning that the adaptive immune system can distinguish between
self and nonself. Nonself molecules serve as antigens, self molecules do not.
● Lymphocytes are the leukocytes that carry out the major features of the adaptive
immune response. They’re divided into B cells and T cells.
● The thymus is an organ located in the upper part of the chest in vertebrates.
- Thymus dependent lymphocytes are called T cells and can recognize and kill host cells
that are infected with a virus.
- Bursa-dependent lymphocytes are called B cells and produce antibodies. They mature in
the bone marrow.
● Lymphocyte origin is where all lymphocytes are produced in bone marrow (a tissue that
fills the internal cavities of bones)
● Lymphocyte maturation: B cells mature in the bone marrow of humans and many other
animal's. T cells mature in the thymus, which is located behind the sternum.
● Lymphocyte activation: Lymphocytes recognize antigens and become activated in the
spleen and the lymph nodes.
- The spleen is an organ located near the stomach in the abdominal cavity and is involved
in destroying old blood cell's.
- Lymph nodes are small, oval organs that are located around the body and they filter the
lymph passing through them. The liquid portion of the lymph originates in fluid that is
forced out of capillaries by blood pressure.
● Lymphocyte transport: Lymphocytes circulate through the blood, lymph nodes and other
organs in the immune system such as the spleen. Lymph is transported throughout the
body via lymphatic ducts, which are thin-walled tubules. The lymphatic system consists
of all ducts and organs involved in the production, maturation and activation of
lymphocytes.
● The immune system cells that are found in mucous secreting tissues are called mucosa-
associated lymphoid tissues (MALT). They guard points of pathogen entry.
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● B cells can produce antibodies to many different antigens and each antibody is specific
to a particular antigen. B-cell receptors (BCRs) are proteins that have the same overall
structure of the antibodies produced by B cells that are secreted into the blood.
● The BCR protein consists of a smaller polypeptide called the light chain and a larger
polypeptide called the heavy chain.
- Each BCR has two copies of the light chain and two copies of the heavy chain. They’re
held together by disulfide bonds.
- Each heavy chain includes a transmembrane domain that anchors the BCR in the
plasma membrane of the cell.
● The BCR and antibodies produced by the B cell's are part of family of proteins known as
immunoglobulins. There are 5 classes of immunoglobulins: IgG, IgD, IgE, IgA and IgM.
The classes are distinguished by unique amino acid sequences in the heavy chains and
each has a distinct function in the immune system.
● T cells require other cells to produce the antigens and present them to the T-cell
receptors (TCRs). For a TCR to recognize an antigen, the foreign molecule must first
undergo a complex process called antigen presentation.
- T cell's only bind to antigens that are displayed by other cells of the immune system.
- TCR is composed of two protein chains: (1) the alpha chain and (2) the beta chain.
- The TCRs shape depends on one of the two “Arms” of the antibody or BCR.
● Antibodies, TCRs and BCRs don’t bind to entire antigens, they bind to a selected region
of the antigen called the epitope.
- Antibodies and BCRs bind to epitopes that are part of an intact antigen. TCRs bind to
epitopes that have been processed and presented by other cell's.
● Light chains and heavy chains have two regions : (1) Constant “C” Region and (2)
Variable “V” Region.
- The V regions of heavy and light chains in a BCR are adjacent to one another and face
away from the plasma membrane.
- TCRs also have V and C regions, which are arranged like those in BCRs.
● A self molecule is a molecule belonging to the host.
● Regulatory T cells limit the intensity of normal response by suppressing certain parts of
the immune system, and may help inhibit any self-reactive cells that slip through the self
education system. Defective regulatory T cells are a factor in immune disorder diseases.
Chapter 48.4 Adaptive Immunity: Activation
● The clonal selection theory states that:
1. Antigens are recognized by receptors on B cells and T cell's
2. Lymphocytes require receptor-epitope binding to become activated.
3. Activated lymphocytes are cloned.
4. Activated lymphocytes endure.
● Leukocytes known as Dendritic cells gobble up antigens and debris via phagocytosis.
Take information from the infection site and bring back to lymph nodes and present
antigens to T cells (This is antigen presentation).
● T cells are divided into CD4+ and CD8+ based on the proteins on their membranes
surface.
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Document Summary
Leukocytes involved in the ability to recognize specific antigens and to differentiate between species and even different strains of pathogens can customize their response to particular invades. Antibodies are secreted proteins that bind to a specific part of a specific antigen. The adaptive immune system can recognize and respond to a seemingly limitless array of antigens. Nonself molecules serve as antigens, self molecules do not. Lymphocytes are the leukocytes that carry out the major features of the adaptive immune response. They"re divided into b cells and t cells. The thymus is an organ located in the upper part of the chest in vertebrates. Thymus dependent lymphocytes are called t cells and can recognize and kill host cells that are infected with a virus. Bursa-dependent lymphocytes are called b cells and produce antibodies. Lymphocyte origin is where all lymphocytes are produced in bone marrow (a tissue that fills the internal cavities of bones)
