Chapter 8 Adaptive Immunity Flashcards
Two main types of lymphocytes
B cells (mature in bone marrow) T cells (mature in thymus)
Two main types of adaptive immunity
Humoral immune responses and cell mediated immune responses.
Humoral immunity
The component of the immune system involving antibodies that are secreted by B cells and circulate as soluble proteins in blood plasma and lymph.
Cell-mediated immunity
immunity conferred to an individual through the activity of T cells, involving the direct destruction of viruses, foreign particles, etc. Involves cytotoxic T-cells and Helper T-cells.
Adaptive immunity
Is the body’s ability to recognize and defend itself against distinct invaders and their products.
5 attributes of adaptive immunity
1) Specificity
2) Inducibilty (only acting when you need it)
3) Clonality (clonal selection theory)
4) Unresponsiveness to self (tolerance)
5) Memory (very important regarding vaccination)
Lymphatic System
Screen tissues of the body for foreign antigens. Composed of lymphatic vessels and cells, tissues, and organs.
Lymphatic vessels and the flow of lymph
One-way system that conducts lymph from tissues and returns it to the circulatory system via left subclavian vein.
Lymph
Liquid with similar composition to blood plasma. Arises form fluid leaked form vessels into surrounding tissues.
Primary (central) lymphoid organs
Where cells undergo maturation. Red bone marrow and thymus.
Secondary lymphoid organs
Where matured cells reside and function. Lymph nodes, spleen, tonsils, mucosa-associated lymphatic tissue (MALT)
Lymph nodes
Are small bean shaped structures in the body that carry lymph fluid, nutrients, and waste material between the body tissues and the bloodstream.
Antigens
Molecules the body recognizes as foreign and worthy to attack. Provoke a specific immune response. Recognized by three-dimensional regions called epitomes. Food and dust can be considered antigenic particles.
Exogenous antigens
Are antigens that have entered the body from the outside, for example by inhalation, ingestion, or injection.
Endogenous antigens
Are antigens that have been generated within previously-normal cells as a result of normal cell metabolism, or because of viral or intracellular bacterial infection.
Autoantigen
Is usually a normal protein or complex of viral or intracellular bacterial infection.
B Lymphocytes (B cells) and antibodies
Arise and mature in the bone marrow. Found primarily in the spleen, lymph nodes, and MALT. Small % of B cells circulate in the blood. Major function is the secretion of antibodies.
Specificity of the B cell receptor (BCR)
Each B cell has multiple copies of the B cell receptor. Each B cell generates a single BCR. Two variable regions of the BCR form the antigen binding sites. Each BCR only recognizes only one epitope. The entire repertoire of an individuals BCRs is capable of recognizing millions of different epitopes.
Specificity and Antibody structure of B cells
Antibodies are immunoglobulins similar to BCRs. Secreted by activated B cells called plasma cells. Have identical antigen-binding sites and antigen specificity as the BCR of the activated B cell.
Antibody function
Antigen-binding sites are complementary to epitomes. Antibodies function is several ways:
1) Neutralization
2) Opsonization
3) Killing by oxidation
4) Agglutination
5) Activation of complement & inflammation
Classes of antibodies
Class involved in the immune response depends on the type of antigen, portal entry, and antibody function needed. 5 classes IgM, IgG, IgA, IgE, IgD
IgM
First antibody produced (pentameric)–> Primary response
IgG
Most common and longest-lasting antibody (memory response)
IgA
Associated with body secretions (dimeric)
IgE
Involved in response to parasitic infections and allergies.
IgD
Function unknown
T Lymphocytes (T cells)
Produced in bone marrow and matures in Thymus. Circulates in lymph and blood and migrates to the lymph nodes, spleen and Peyer’s Patches. Antigen binding sites are complementary to epitomes. Have T-cell receptors on their cytoplasmic membrane.
Specificity of the T cell receptor
TCRs do not recognize epitomes directly. TCRs only bind epitopes associated with a MHC protein. TCRs act primarily against cells that harbor intracellular pathogens. TCR cannot get secreted (BCR can)
Epitopes
A localized region on the surface of an antigen that is capable of eliciting an immune response and of combining with a specific antibody to counter that response.
Types of T lymphocytes
Are based on surface glycoproteins and characteristic functions. Three types: Cytotoxic T lymphocyte (CD8+), Helper T lymphocyte (CD4+), Regulatory T lymphocyte.
Cytotoxic (CD8) T cells
Directly kills other cells (virally infected)
Helper (CD4) T cells
Helps regulate the activities of B cells (Th2) and cytotoxic T cells (Th1)
Regulatory T lymphocyte
Represses adaptive immune responses
Clonal deletion of auto-reactive B cells
It is vital that immune responses not be directed against autoantigen. Body eliminates self-reactive lymphocytes. The immature B cells whose BCRs bind too strongly to self antigens will not be allowed to mature. If B cells are found to be highly reactive to self they are induced to undergo apoptosis. This happens in the bone marrow for B cells.
Clonal deletion of auto-reactive T cells in the Thymus
During their maturation in the thymus, lymphocytes that react to autoantigens are eliminated by being induced to undergo apoptosis.
Thymocyte TCR generation deletion of auto reactive cells
Functional (positive) selection and Autoreactive (negative selection).
Functional (positive) Selection
Thymocytes generate TCR as well as CD4 and CD8. Receptors interact with MHC and HLA antigens to select for correctly assemble receptors.
Positive selection eliminates weakly binding cells by apoptosis. Only high-binding cells (TCR binding to MHC I/II or peptide) are selected.
Autoreactive (negative selection)
Thymocytes in the medulla undergo selection against TCR reactivity with auto-antigens. Autoreactive cells are deleted by apoptosis. There is some clonal amplification and cells become single-positive (i.e., either expressing CD4 (Th) or CD8 (CTL).
Cytokines
Cells of immune system communicate by releasing soluble regulatory proteins that act on other cells. Cytokines secreted by various leukocytes. The complex web of signals among all the cells of the immune system is called the cytokine network. The cell receives the information from cytokine-activated receptor to produce another messenger.
Interleukins (ILs)
Signal among leukocytes and other tissues.
Interferons (IFNs)
Antiviral proteins that may act as cytokines.
Growth factors
Proteins that stimulate stem cells to divide
Tumor necrosis factor (TNF)
Secreted by macrophages and T cells to kill tumor cells and regulate immune responses and inflammation.
Chemokines
Chemotactic cytokines that signal leukocytes to move.
Roles of MHC
Group of antigens first identified in graft patients. Important in determining compatibility of tissues for tissue grafting. MHC antigens are glycoproteins found in the membranes of most cells of vertebrate animals. Hold and position antigenic determinates for presentation to T cells. Antigens bind in the antigen-binding groove of MHC molecules.
