Chapter 34. The Immune System Flashcards
polypeptide segments in immunoglobulin L and H chains which display great sequence variability and which are responsible for antigenic specificity.
Complementarity-determining region (CDR)
One of two 50-kd polypeptide chains produced when immunoglobulin G (IgG) is cleaved by the protease papain; the Fc fragment of an intact IgG molecule cannot participate in antigen binding but can mediate other important biological activities, such as complement fixation.
Fc
One of two 50-kd polypeptide chains produced when immunoglobulin G is cleaved by the protease papain; Fab fragments bind antigens but cannot cross-link them, because each fragment has only one binding site for an antigen.
Fab
a system for recognition of foreign substances that employs soluble antibodies to bind to and inactivate such substances.
Humoral immune response
precursors to plasma cells, which are antibody-secreting cells.
B lymphocyte (B cell)
An evolutionarily ancient defense system that responds rapidly to features present in many pathogens. The innate immune systems includes the epithelial lining that surrounds host cell, phagocytes, and a family of receptors that can recognize specific features present in most pathogens.
Innate immune system
A foreign substance that elicits the synthesis of an antibody.
Antigen
a 50-kd polypeptide that is one of two types of paired chains found in the immunoglobulin G molecule; each heavy (H) chain consists of a variable region and three constant regions, and each chain is linked by a disulfide bond to a light chain.
Heavy (H) chain
A specific molecular characteristic found primarily on invading organisms that is a critical component of the pathogen's function. PAMPs are targets of Toll-like receptors.
Pathogen-associated molecular pattern (PAMP)
The specific site on an antigen that is recognized by an antibody. Also known as an epitope.
Antigenic determinant (epitope)
the major antibody in serum. IgG posses two antigen binding sites.
Immunoglobin G (IgG)
T cells that trigger cell death via apoptosis in cells that display foreign antigens on class I MHC proteins.
Cytotoxic T lymphocyte
A defense system that that responds to specific features present only in a given pathogen that is comprised of a humoral and cellular component. In the humoral immune response, antibodies function as recognition elements that bind to foreign molecules and serve as markers signaling foreign invasion. In the cellular immune response, cytotoxic T lymphocytes destroy cells that have been invaded by a pathogen.
Adaptive immune system
A family of receptors that recognize specific features present in most pathogens and yet not respond to materials normally present in the host.
Toll-like receptor (TLR)
a system for cellular recognition of foreign substances that employs cell-attached T-cell receptors to eliminate cells infected by a pathogen or to elicit a particular antigenic response by stimulating B-lymphocyte antibody production.
Cellular immune response
the carboxyl terminal end of an IgG light chain or an IgG heavy chain. For many antibodies these portions of the polypeptide chains have amino acid sequences that are very similar to one another; a light chain has one constant region, whereas a heavy chain has three such regions, each of which specifies a compact domain in the native immunoglobulin molecule.
Constant region
a 25-kd polypeptide that is one of two types of chains found in immunoglobulin G. Each L chain consists of a variable region and a constant region, and each chain is linked by a disulfide bond to a heavy chain.
Light (L) chain
the major class of antibodies in external secretions, such as saliva, tears, bronchial mucus and intestinal mucus.
Immunoglobin A (IgA)
the first class of antibodies to appear in the serum after exposure to an antigen. IgM posses10 antigen binding sites.
Immunoglobulin M (IgM)
an antibody of unknown function.
Immunoglobin D (IgD)
an antibody that confers protection against parasites. IgE also initiates allergic reactions.
Immunoglobin E (IgE)
mobility imparted to IgG antibodies by a flexible polypeptide that joins the Fc and the two Fabunits. Such mobility enhances the formation of antibody-antigen complexes.
Segmental flexibility
A common structural motif for immunoglobulins, in which two broad sheets of antiparallel β strands enclose hydrophobic side chains, and complementarity-determining regions of variable domains pair to form an antigen-binding site.
Immunoglobulin fold
Immune system cells that ingest and destroy pathogens.
Phagocyte
polypeptide segments in immunoglobulin L and H chains which display great sequence variability and which are responsible for antigenic specificity.
Hypervariable loop
the 108-residue amino acid sequence found at the N-terminal end of both the L and H chains of immunoglobulin G; the sequence in this region varies for every antibody type known; a portion of these segments (the hypervariable regions) form the antigen-binding site of the immunoglobulin.
Variable region
a protein expressed only in antigen-presenting cells that displays peptides derived by the destruction of proteins internalized by endocytosis.
Class II MHC protein
a selection process in T cell development in which T cells that can bind to MHC molecules survive, while those that cannot undergo apoptosis.
Positive selection
T cells that stimulate the proliferation of specific B lymphocytes and cytotoxic T cells.
Helper T cell
a selection process in T cell development in which T cells that bind with high affinity to MHC complexes of antigen-presenting cells displaying self-peptides undergo apoptosis.
Negative selection
a disease, such as insulin-dependent diabetes and multiple sclerosis, that result from the failure to suppress the immune response to self-antigens.
Autoimmune disease
An ABC transporter component of the endoplasmic reticulum that transfers peptides into the endoplasmic for association with MHC I proteins.
TAP (transporter associated with antigen processing) protein
a protein present on the surface of helper T cells that, along with the T cell receptor, binds to class II MHC proteins on antigen-presenting cells. CD4 is the source of the specificity of helper T cells for class II MHC interactions.
CD4
a protein secreted by activated T cells that renders target cells permeable by forming 10 nm pores in the target cell membranes. These pores allow entry of granzymes.
Perforin
Cells which specialize in the production of large amounts of antibody.
plasma cell
a small foreign molecule that can elicit specific antibody formation when attached to a macromolecule. The dinitrophenyl group is effective at eliciting an antigenic response and has been widely used as a haptenic determinant.
Hapten
the intracellular region of Ig-alpha and Ig-beta membrane proteins of immature B cells. Upon antigen binding to the membrane-bound antibodies of the B cell, the ITAM regions of Ig-alpha and Ig-beta are phosphorylated, which initiates pathways leading to cell growth and B-cell differentiation.
Immunoreceptor tyrosine-based activation motif (ITAM)
the receptor that recognizes peptides displayed by MHC proteins on target cells; the protein consists of two different 43-kd chains joined by a disulfide bond and spanning the plasma membrane; the combination of constant and variable regions among various T-cell receptors allows T cells to recognize a large number of different epitopes.
T-cell receptor
integral membrane proteins that bind and display on the cell surface peptides derived from the digestion of proteins from the cytosol (class I MHC proteins) or from endosomal compartments (class II MHC proteins). Foreign peptides bound to class I MHC proteins mark them for destruction by killer T cells, while those bound to class II MHC proteins provide a signal for helper T cells, which can in turn stimulate B lymphocyte production.
Major histocompatibility complex (MHC)
Proteolytic enzymes secreted by activated T cells into target cells to initiate apoptosis.
Granzyme
the step in the differentiation of an antibody producing cells in which the cells switch from producing IgM antibodies to producing one or the other classes of antibodies while maintaining the same antigen specificity.
Class switching
a cell surface protein expressed by cytotoxic T cells that, in conjunction with the T cell receptor, recognizes class I MHC-peptide complexes. CD8 binds to the MHC protein itself.
CD8
The ability of the immune system to respond more rapidly and effectively to pathogens that have been encountered previously.
immunological memory
a membrane glycoprotein of the fetal gastrointestinal cells that is not significantly expressed after birth. High serum levels of CEA are evident in many patients with colorectal cancer.
Carcinoembryonic antigen (CEA)
membrane proteins that tightly bind proteolytic fragments of cellular proteins and present them to the scrutiny of T cells. A foreign protein presented in a class I MHC protein provokes attack by killer T cells that initiate apoptosis in the target cell.
Class I MHC protein
a drug that is a potent suppressor of the immune system and is used to prevent rejection in organ transplants.
Cyclosporine
the cause of acquired immune deficiency syndrome (AIDS). HIV destroys helper T cell by increasing the permeability of the T cell membrane. Loss of the helper T cells severely cripples the immune system, rendering the victim susceptible to many types of infection.
Human immunodeficiency virus (HIV)
The name given to a member of the major-histocompatibilitycomplex proteins in human beings.
Human leukocyte antigen (HLA)
Vaccines that contain pathogens that have been rendered harmless by treatment with chemicals or high heat.
killed, or inactivated, vaccines
Vaccines that contain live pathogens that have accumulated mutations so that they are no longer virulent to human cells. These vaccines are most commonly generated by repeated infection of the pathogen in cultured cells until its virulence is lost.
live attenuated vaccines
Vaccines that contain a purified protein component of the pathogen. Such proteins can be either isolated from infected material (such as blood from chronically infected patients) or generated by recombinant methods.
subunit vaccines
Vaccines that are used against pathogens that employ an extracellular toxin to cause disease. These vaccines contain a form of the toxin that has been inactivated by treatment with chemicals or high heat.
toxoid vaccines
A means to increase antibody diversity by recombining different variable (V) genes, joining (J) genes, and diversity (D) genes to generate the entire variable regions of antibody chains; the D genes undergo recombination only in antibody heavy chains.
V(D)J recombination
A biological preparation of inactivated forms of a pathogen that is administered to protect against subsequent infection with the active pathogen.
Vaccine
An immunoglobulin fold-containing subunit of human class I MHC protein; this 12-kd polypeptide is noncovalently bound to the 44-kd a chain.
β2-microglobulin
