Chapter 8 Flashcards, Adaptive Immunity
What is adaptive immunity?
The third line of defense, consisting of lymphocytes and antibodies, developing slowly and specifically in response to infectious agents.
How does adaptive immunity compare to innate immunity?
It is slower, specific, and has memory, making it longer-lived than the innate inflammatory response.
What initiates the adaptive immune response?
Cells of the innate system process and present antigens to lymphocytes in peripheral lymphoid tissue.
What are the two types of lymphocytes involved in adaptive immunity?
B lymphocytes and T lymphocytes, each with distinct functions.
What is the role of B cells in adaptive immunity?
They are responsible for humoral immunity mediated by circulating antibodies.
What is the role of T cells in adaptive immunity?
They are responsible for cell-mediated immunity, killing targets directly or stimulating other leukocytes.
What is clonal diversity?
The extensive diversity of antigen receptors in B and T cells capable of recognizing different antigens.
What is antigen processing?
The process by which phagocytic cells, primarily dendritic cells, process antigens for presentation to lymphocytes.
What are antigen-presenting cells (APCs)?
Cells that present processed antigens to lymphocytes, defining clonal selection involving subsets of B and T cells.
What do B cells develop into?
Plasma cells that produce antibodies.
What are the subsets of T cells?
T-cytotoxic (Tc cells), T-helper (Th cells), and T-regulatory (Treg cells).
What is the humoral immune response?
The arm of the immune response primarily responsible for protection against bacteria and viruses, mediated by antibodies.
What is the cellular immune response?
The arm of the immune response that defends against intracellular pathogens and cancer cells, mediated by effector T cells.
What is active immunity?
Immunity produced by an individual after natural exposure to an antigen or immunization.
What is passive immunity?
Immunity that does not involve the host’s immune response, occurring when preformed antibodies or T lymphocytes are transferred.
How can passive immunity occur?
Naturally, through maternal antibodies to the fetus, or artificially, through immunotherapy.
What are antigens?
Antigens are molecules that can react with components of the adaptive immune system, including antibodies and lymphocyte surface receptors.
What are immunogens?
Immunogens are antigens that can initiate the adaptive immune response.
What characteristics must an antigen have to be immunogenic?
An antigen must be of the correct type, size, and complexity and be present in sufficient quantities.
What are haptens?
Haptens are small-molecular-weight antigens that are not themselves immunogenic.
How do B and T lymphocytes bind antigens?
B and T lymphocytes bind antigen through cognate receptor complexes on their surfaces.
What are the receptor complexes on B and T lymphocytes?
The receptor complexes are the BCR (B Cell Receptor) and TCR (T Cell Receptor) complexes.
What is the antigen-binding molecule of the BCR?
The antigen-binding molecule of the BCR is antibody.
What are antibodies composed of?
Antibodies are composed of four polypeptide chains—two identical heavy chains and two identical light chains—held together by disulfide bonds.
What determines the class of an antibody?
The class of antibody is determined by which constant regions make up their heavy chains.
What are the classes of antibodies?
The classes include IgG, IgA, IgE, IgD, and IgM.
What are the parts of an antibody that bind antigen called?
The parts of antibody that bind antigen are called the Fab.
What is the Fc region of an antibody?
The Fc region is the part that reacts with cells and molecules of the innate system.
Where does antigen bind on antibodies?
Antigen binds to hypervariable regions (complementary-determining regions, or CDRs) of both the heavy and the light chains.
How are endogenous protein antigens presented?
Endogenous protein antigens are presented by class I molecules of MHC.
How are exogenous protein antigens presented?
Exogenous protein antigens are presented by class II MHC molecules.
How are lipid antigens presented?
Lipid antigens are presented by CD1.
What is the MHC?
The MHC is a cluster of genes found on human chromosome 6.
What are HLA antigens?
The products of MHC genes are also called HLA antigens.
What is the significance of MHC genes being polymorphic?
MHC genes are highly polymorphic, having many different possible alleles.
How many alleles does an individual carry at each MHC locus?
An individual will carry only two alleles at each locus, one from each parent.
What defines an individual’s MHC haplotype?
The particular combination of alleles that individuals carry defines their MHC haplotype.
What is required for an immune response to develop?
A variety of cells must interact through surface adhesion molecules.
How do cells communicate during immune responses?
Cells communicate through soluble cytokines.
What roles do cytokines play in the immune response?
Cytokines have multiple functions in the adaptive immune response, including both positive and negative regulation of B-cell and T-cell maturation.
What determines a cell’s response in the immune system?
It is the precise combination of cytokines influencing a given cell that ultimately determines that cell’s response.
Where does the generation of clonal diversity occur?
In the primary lymphoid organs: thymus for T cells and bone marrow for B cells.
What is the collective ability of an individual’s T cells and B cells?
To respond to virtually any antigen due to genetic rearrangement of genes for TCR and BCR.
What results from the rearrangement of V and J genes?
The variable regions of the TCR α chain and the BCR light chain.
What results from the rearrangement of V, D, and J genes?
The variable regions of the TCR β chain and the BCR heavy chain.
What surface markers are expressed during differentiation of B cells and T cells?
CD4 on helper T cells, CD8 on cytotoxic T cells, and CD21 and CD40 on B cells.
What process eliminates B cells and T cells that produce receptors against self-antigens?
Central tolerance.
What are the characteristics of cells leaving the primary lymphoid organs?
They are immunocompetent and capable of reacting to antigens.
What is clonal selection?
The process by which antigen selects lymphocytes with complementary TCRs or BCRs to induce an immune response.
What is required for lymphocyte activation?
Most antigens must be processed and presented by an APC with the appropriate molecule (MHC class I, MHC class II, or CD1).
What role do T-helper cells (Th cells) play in immune responses?
They are required for most immune responses and interact with APCs to develop into Th1 or Th2 subsets.
What do Th1 cells do?
Help activate macrophages and cytotoxic T cells.
What do Th2 cells do?
Help activate B cells.
What is the function of Th17 cells?
Provide help in developing inflammation and attracting neutrophils and macrophages.
How are B cells activated?
By recognizing soluble antigen via the BCR, processing the antigen, and presenting it to Th2 cells.
What is required for B-cell activation besides antigen recognition?
Interactions with Th2 cells through adhesion molecules like CD40 and CD40L.
What can B cells undergo as a result of Th2 cell cytokines?
Class-switching from making IgM to IgA, IgE, or IgG.
What are the two phases of the humoral immune response?
Primary and secondary phases, differing in IgG amounts and response speed.
What happens to B cells upon activation?
They proliferate and differentiate into plasma cells or memory B cells.
How is T-cell activation achieved?
Through recognition by the TCR and CD8 of antigen presented by MHC class I.
What is necessary for efficient T-cell differentiation?
Intercellular adhesion molecules and cytokines like IL-2 from Th1 cells.
What do T cells become upon activation?
Cytotoxic T lymphocytes (CTLs) or memory T cells.
What are superantigens?
Molecules that activate a large number of Th cells and cause excessive cytokine production.
What can superantigens lead to?
Shock and death of the patient due to excessive proinflammatory cytokines.
What are examples of superantigens?
Bacterial toxins that can cause toxic shock syndrome and food poisoning.
What are the two categories of mechanisms by which antibodies affect antigens?
Antibodies affect antigens through direct and indirect mechanisms.
What mediates direct mechanisms of antibody action?
Direct mechanisms are mediated by the antigen-binding portions of antibodies (the Fab portions containing the variable regions).
What are the results of direct mechanisms of antibody action?
Direct mechanisms result in neutralization of the biologic activity of antigens and possibly removal of the antigen by agglutination or precipitation.
What do indirect mechanisms of antibody action depend on?
Indirect mechanisms depend on both the Fab and the non–antigen-binding portion of antibodies (the Fc portions containing the constant regions).
How do antibodies of the systemic immune system function?
Antibodies of the systemic immune system function throughout the body.
What is the primary class of immunoglobulins associated with the secretory immune system?
The primary class of immunoglobulins associated with the secretory immune system is IgA.
What is the role of T-cytotoxic cells (Tc cells)?
Tc cells adhere to antigen presented by MHC class I on target cells and kill the target by apoptosis.
How do NK cells recognize their targets?
NK cells recognize target cells that do not express MHC class I.
What cytokine do Th1 cells secrete to activate M1 macrophages?
Th1 cells secrete interferon-γ (IFN-γ) to activate M1 macrophages.
What do Th2 cells secrete to activate M2 macrophages?
Th2 cells secrete cytokines such as IL-4 and IL-13 to activate M2 macrophages.
What is the function of Th17 cells?
Th17 cells secrete cytokines that recruit phagocytic cells to a site of inflammation.
What is the role of T-regulatory (Treg) cells?
Treg cells control the immune response, usually suppressing it and maintaining tolerance against self-antigens.
What do B-regulatory (Breg) cells do?
Breg cells control peripheral tolerance through the production of immunosuppressive cytokines.
How is the immune response of a human neonate characterized?
The human neonate has a poorly developed immune response, particularly in the production of IgG.
How are maternal antibodies involved in neonatal immunity?
Maternal antibodies protect the fetus and neonate in utero and during the first few postnatal months.
When do maternal antibodies disappear in the neonate?
Maternal antibodies disappear by about 10 months of age.
What happens to total IgG levels in the umbilical cord at birth?
Total IgG levels in the umbilical cord are near adult levels at birth.
When does a neonate begin producing IgG?
The neonate begins producing IgG at birth.
What is observed in T-cell activity in older adults?
T-cell activity is deficient in older adults.
What change is observed in T-cell subsets in older adults?
A shift in the balance of T-cell subsets is observed in older adults.
How does antibody production to specific antigens change in older adults?
Antibody production to specific antigens is inferior in older adults.
What is a common characteristic of circulating autoantibodies in older adults?
Older adults tend to have increased levels of circulating autoantibodies.
