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54 Cards in this Set
- Front
- Back
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The Third and Final Line of Defense
• Not innate, but adaptive • Acquired only after an immunizing event such as an infection • Antigens stimulate a response by T and B cells |
specific immunity
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the ability of the body to react
with myriad foreign substances – Development of B and T lymphocytes – The lymphocytes become specialized for reacting only to one specific antigen or immunogen |
Immunocompetence
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Two characterizing features of the third line of defense
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– Specificity
– Memory |
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5 Main Stages of Immunologic
Development and Interaction |
• Lymphocyte development and differentiation
• The presentation of antigens • The challenge of B and T lymphocytes by antigens • B lymphocytes and the production and activities of antibodies • T lymphocyte responses |
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An Overview of Specific Immune
Responses • Development of the Dual Lymphocyte System |
– All lymphocytes arise from the same basic stem
cell type – Final maturation of B cells occurs in specialized bone marrow sites – Maturation of T cells occurs in the thymus – Both cell types then migrate to separate areas in the lymphoid organs |
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Entrance and Presentation of Antigens and Clonal Selection
• _______ cross the first line of defense and enter the tissue • ______ migrate to the site • _______ ingest the pathogen and induce an inflammatory response if appropriate • _______ ingest the antigen and migrate to the nearest lymphoid organ – Process and present antigen to ______ • Pieces of antigen drain into _____ – Activate B cells |
Foreign cells
Phagocytes Macrophages Dendritic cells T lymphocytes lymph nodes |
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Activation of Lymphocytes and Clonal Expansion
• When challenged by antigen, ___ and ____ proliferate and differentiate • This creates a_____ (group of genetically identical cells) • Some become ______ |
B ,T cells
clone memory cells |
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Products of B Lymphocytes: Antibody
Structure and Functions • Progeny of dividing B-cell clone are called _______ • Programmed to synthesize and secrete ______ into tissue fluid and blood • When ______ attach to antigen, the antigen is marked for destruction or neutralization • ______ immunity |
plasma cells
antibodies antibodies Humoral |
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how T cells respond to antigen
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cell-mediated immunity
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• When activated by antigen, ____ gives rise to one of three different types of progeny
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T cell
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activate macrophages and help activate
TC cells |
Th1 cells
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assist B-cell processes
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Th2 cells
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lead to the destruction of infected host
cells and other “foreign” cells |
Tc cells
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– Attachment to non-self or foreign antigens
– Binding to cell surface receptors that indicate self, such as MHC molecules – Receiving and transmitting chemical messages to coordinate the response – Aiding in cellular development |
immune system receptors
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• Set of genes that codes for human cell receptors
• Gives rise to a series of glycoproteins (MHC molecules) found on all cells except red blood cells • Also known as human leukocyte antigen (HLA) system • Three classes of MHC genes identified: |
Major Histocompatibility Complex
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code for markers that display unique characteristics of self
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Class I genes
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code for immune regulatory receptors found on
macrophages, dendritic cells, and B cells; and are involved in presenting antigens to T cells during cooperative immune reactions |
Class II genes-
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encode proteins involved with the complement system
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Class III genes-
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have receptors that bind antigens
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B cells
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have receptors that bind processed antigens plus MHC molecules on the cells that present antigens to them
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T cells
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The Origin of Diversity and Specificity of the Immune Response
– Early undifferentiated lymphocytes in the embryo, fetus, and adult bone marrow undergo a continuous series of divisions and genetic changes – Generates hundreds of millions of different types of B and T cells |
The Clonal Selection Theory and Lymphocyte Development
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Summary of the Mechanism
• Stem cells in bone marrow can become _____, _____, & _____ • Lymphocytic cells become either ____ or _____ • Cells destined to become B cells stay in ______ • T cells migrate to the _____ where they build their unique antigen receptor • B and T cells then migrate to ________________ |
granulocytes, monocytes, or lymphocytes
T cells or B cells bone marrow thymus secondary lymphoid tissues |
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• Does not require the actual presence of foreign antigens
• By the time T and B cells reach the lymphoid tissues, each one is equipped to respond to a single unique antigen • This diversity is generated by rearrangements of the gene segments that code for the proteinaceous antigen receptors on the T and B cells • Each genetically unique line of lymphocytes arising from these recombinations |
Proliferative Stage of Development
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• Second stage of development
• Requires stimulation by an antigen • Antigen contact with a lymphocyte stimulates the clone to undergo mitotic divisions |
Clonal Selection and Expansion
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• Lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues
• Each genetically distinct lymphocyte expresses only a single specificity and can react to only one type of antigen |
Two Important Generalities From the Clonal Selection Theory
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Any clones that react to self are destroyed during development through
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clonal deletion
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thought to be caused by the loss of immune tolerance to self
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Autoimmune diseases
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An
Immunoglobulin Molecule • The receptor genes that undergo recombination are those governing immunoglobulin (Ig) synthesis • Y-shaped arrangement • Ends of forks contain pockets called the antigen binding sites – Can be highly variable in shape to fit a wide range of antigens – Variable regions (V) |
The Specific B-Cell Receptor
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large glycoprotein molecules that serve as the
antigen receptors of B cells and as antibodies when secreted |
Igs
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• Belongs to the same protein family as the Bcell
receptor • Relatively small and never secreted |
T cell receptors
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– Bone marrow sites harbor stromal cells
– Stromal cells nurture the lymphocyte stem cells and provide chemical signals that initiate B-cell development – B cells circulate through the blood, “homing” to specific sites in lymph nodes, spleen, and GALT – Adhere to specific binding molecules where they come into contact with antigens |
Specific Events in B-Cell Maturation
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Directed by the thymus gland and its hormones
• Mature T lymphocytes express either CD4 or CD8 coreceptors • Constantly circulate between the lymphatic and general circulatory system, migrating to specific T-cell areas of the lymph nodes and spleen |
specific events in T cell maturation
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binds to MHC class II, expressed on T helper cells
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CD4
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binds to MHC class I, found on cytotoxic T cells
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CD8
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a substance that provokes an immune response in specific lymphocytes
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Antigen (Ag):
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the property of behaving as an antigen
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Antigenicity
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another term for an antigen
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Immunogen
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• Characteristics of Antigens
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– It is perceived as foreign
– Complex molecules are more immunogenic - categories |
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– Categories of antigens
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• Proteins and polypeptides
• Lipoproteins • Glycoproteins • Nucleoproteins • Polysaccharides |
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Substance must be large enough to initiate an ________ from the surveillance cells
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immune response
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Lymphocyte recognizes and responds to only a portion of the antigen molecule
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the epitope
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very complex with numerous component parts, each of which elicit a separate lymphocyte response
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Mosaic antigens
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small foreign molecules that consist of only a determinant group
– Too small to elicit an immune response on their own – If linked to a larger carrier molecule, then the combination develops immunogenicity |
haptens
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cell surface markers and
molecules that occur in some members of the same species but not in others |
Alloantigens
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bacterial toxins, potent
stimuli for T cells |
Superantigens
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antigens that evoke allergic
reactions |
Allergens
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cells that act upon and formally present antigens to lymphocytes
• Macrophages • B cells • Dendritic cells – Engulf the antigen and modify it so it is more immunogenic and recognizable |
Antigen-presenting cells (APCs):
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After processing, the antigen is bound to the _______ and moved to the surface of the APC so it is
accessible to T lymphocytes |
MHC receptor
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APCs activate _______ cells in the lymph nodes
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CD4 T helper
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CD4 helper T cells have an ______ that:
• Binds to MHC class II • Binds to a piece of the antigen • Binds to a piece of the CD4 molecule (which also binds to MHC class II) |
antigen-specific T-cell receptor
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Once identification has occurred, a molecule on the ___ activates the T helper cell
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APC
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TH produces ______
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interleukin-2 (IL-2)
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The T helper cells can now help activate _____
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B cells
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Clonal
Expansion and Antibody Production – Clonal selection and binding of antigen – Antigen processing and presentation – B-cell/T-cell recognition and cooperation – B-cell activation – Clonal expansion – Antibody production and secretion |
Activation of B Lymphocytes
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