BIOL 250 - Chapter 16: Adaptive Immunity

adaptive immunity

the body's ability to recognize and defend against distinct species or strains of invaders; only present in vertebrates

five attributes of adaptive immunity

specificity, inducibility, clonality, unresponsiveness to self, memory

specificity

a particular response is specific to the "attacker"

inducibility

the specific antigen-containing pathogen activates or induces cells of adaptive immunity

clonality

once induced, cells of the adaptive immune system proliferate to form many generations of nearly identical cells

unresponsiveness to self

adaptive immune cells do not attack normal body cells

memory

adapts to respond faster and more effectively in subsequent encounters with a particular pathogen

lymphocyte

main actor of the adaptive immune system; type of agranulocyte that originates in the red bone marrow and has nuclei that nearly fill the cell

two types of lymphocytes

B lymphocytes (B cells) and T lymphocytes (T cells)

B lymphocytes (B cells)

arises and matures in red bone marrow in adults; found in spleen, lymph nodes, red bone marrow and Peyer's patches of the intestines; secretes antibodies

T lymphocytes

matures in the thymus and acts primarily against endogenous antigens

antibodies

a protective protein secreted by descendants of a B cell that recognizes and strongly binds to the specific biochemical shape of the antigen

two basic types of adaptive responses

humoral response and cell-mediated response

humoral response (antibody immune response)

B lymphocytes attack extracellular pathogens; involves soluble proteins called antibodies

cell-mediated response

T lymphocytes respond against intracellular pathogens

lymphatic system

body system composed of lymphatic vessels and lymphoid tissues and organs

lymphatic vessels

tubes that conduct lymph

lymph

a colorless, watery liquid similar in composition to blood plasma

antigen

molecule that triggers a specific immune response

immunogenicity

the degree to which an antigen provokes an immune response; varies and depends on an antigen's biochemical features

epitopes

the three-dimensional shape of a region of an antigen that is recognized by the immune system

exogenous antigens

come from outside the body's cells and include toxins and other secretions and components of microbial cell walls, membranes, flagella and pili

endogenous antigens

produced by protozoa, fungi, bacteria and viruses that reproduce inside a body's cells; only responded to when such cells incorporate antigens into their cytoplasmic membrane

autoantigens

antigenic molecules derived from normal cellular processes

major histocompatibility complex (MHC)

group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances

two classes of MHC proteins

class I MHC proteins and class II MHC proteins

antigen-presenting cells (APCs)

dendritic cells, macrophages and B cells, which process antigens and activate cells of the immune system

dendritic cells

cells of the epidermis and mucous membranes that devour pathogens

processing endogenous antigens

1. each antigen is cut into smaller pieces (with their epitopes) and moved into the ER and bind to complementary antigen-binding grooves of MHC class I molecules in the ER
2. the ER membrane with lots of MHC class I proteins and epitopes is packaged to form vesicles
3. each vesicle fuses the the cytoplasmic membrane so that the vesicle's membrane becomes part of the cytoplasmic membrane
4. the cell displays the MHC I protein-epitope complex on the cell's surface
5. since each nucleated cell in the body makes class I MHCs, each cell displays epitopes from every endogenous antigen and every autoantigen inside that cell, allow for detection of all antigens inside cells

processing exogenous antigens

1. a dendritic cell phagocytizes a pathogen and a lysosome with class II MHC molecules in its membrane fuses with the phagosome and clips antigens into epitopes within the phagolysosome
2. vesicle fuses with cytoplasmic membrane
3. MHC II-epitope complexes are left on cell's surface
4. empty MHC II molecules are degraded

T cell receptor (TCR)

antigen receptor generated in the cytoplasmic membrane of T lymphocytes

three types of T cells

cytotoxic, helper, regulatory

cytotoxic T cell (Tc)

directly kill infected or abnormal cells (like cancer cells)

helper T cells (Th)

help regulate the activities of B cells and Tc cells during immune responses by providing necessary signals and growth factors

two types of Th cells

type 1 Th cells (Th1) and type 2 Th cells (Th2)

type 1 helper T cells

assist Tc cells and stimulate and regulate innate immunity

type 2 helper T cells

function in conjunction with B cells

regulatory T cells (Tr)

activated by contact with other immune cells and secrete cytokines different from those secreted by helper T cells

clonal deletion

process by which cells with receptors that respond to autoantigens are selectively killed via apoptosis

apoptosis

programmed cell suicide

B cell receptor (BCR)

antibody integral to the cytoplasmic membrane and expressed by B cells; a type of immunoglobulin made of six polypeptide chains

parts of a BCR

heavy chains, light chains, disulfide bonds, transmembrane portion, variable region, antigen-binding sites

antigen-binding sites

site formed by the variable regions of a heavy and light chain of an antibody; bind epitopes and account for the specificity of an antibody immune response

plasma cells

B cells that are actively fighting against exogenous antigens and secreting antibodies

five ways that antibodies function

activation of complement and inflammation, neutralization, opsonization, agglutination, and antibody-dependent cell-mediated cytotoxicity

activation of complement and inflammation

antibodies trigger the complement cascade and stimulate the release of inflammatory mediators. IgE bound to antigen also attaches its stem to mast cells, eosinophils, and basophils, triggering the release of inflammatory chemicals

neutralization

the action of a toxin or attachment of a pathogen is blocked; antibodies bind to a critical portion of the toxin so that it can no longer harm the body

opsonization

antibodies act as opsonins, stimulating phagocytosis; changing the surface of an antigen so as to enhance phagocytosis

agglutination

aggregation caused when antibodies bind to two antigens, hindering the activity of pathogenic microorganisms and increase probability of phagocytosis

antibody-dependent cell-mediated cytotoxicity (ADCC)

process whereby NK cells lyse cells covered with antibodies; different from opsonization in that the target dies by apoptosis

perforin-granzyme pathway (used in ADCC)

NK cell releases perforin and granzyme which triggers apoptosis

perforins

makes pore complex in a virally infected cell

granzyme

moves through pore and activates apoptosis enzymes

five classes of antibodies

IgM, IgG, IgA, IgE, IgD

immunoglobulin M (IgM)

the second most common antibody class and the predominant antibody produced first during a primary humoral immune response; most efficient at complement activation, which triggers inflammation. Can also be involved in agglutination and neutralization

immunoglobulin G (IgG)

the predominant antibody class found in the bloodstream and the primary defender against invading bacteria; has many functions including roles in complement activation, opsonization, neutralization, and ADCC

immunoglobulin A (IgA)

the antibody class most commonly associated with various body secretions, including tears and milk. IgA pairs with a secretory component to form secretory IgA

secretory IgA

the combination of IgA and a secretory component, found in tears, mucous membrane secretions, and breast milk, where it agglutinates and neutralizes antigens

immunoglobulin E (IgE)

signal antibody molecule that triggers the inflammatory response, particularly in allergic reactions and infections by parasitic worms

immunoglobulin D (IgD)

a membrane-bound antibody molecule found in some animals as a B cell receptor

cytokines

soluble regulatory proteins that act as intercellular signals to direct activities in immune responses

five types of cytokines

interferons (IFNs), interleukins (ILs), growth factors, tumor necrosis factors (TNFs), and chemokines

interleukins (ILs)

immune system cytokines that signal among leukocytes

interferons (IFNs)

protein molecules that inhibit the spread of viral infections

growth factors

organic chemical, such as a vitamin, required in very small amounts for metabolism. In immunology, an immune system cytokine that stimulates stem cells to divide, ensuring that the body is supplied with sufficient leukocytes of all types

tumor necrosis factor (TNF)

an immune system cytokine secreted by macrophages and T cells to kill tumor cells and to regulate immune responses and inflammation

chemokines

an immune system cytokine that signals leukocytes to rush to the site of inflammation or infection and activate other leukocytes

four ways acquired immunity is categorized

natural or artificial and active or passive

naturally acquired immunity

when the body mounts an immune response against antigens (ex. influenza viruses, food antigens) encountered in daily life

artificially acquired immunity

the body's response to antigens introduced in vaccines, as occurs with immunization against tetanus and flu

active immunity

the immune system responds actively to antigens via antibody or cell-mediated responses

passive immunity

the body passively receives antibodies from another individual

four types of acquired immunity

naturally acquired active immunity, naturally acquired passive immunity, artificially acquired active immunity, and artificially acquired passive immunity

naturally acquired active immunity

type of immunity that occurs when the body responds to exposure to antigens by mounting specific immune responses

naturally acquired passive immunity

type of immunity that occurs when a fetus, newborn, or child receives antibodies across the placenta or within breast milk

artificially acquired active immunity

type of immunity that occurs when the body receives antigens by injection, as with vaccinations, and mounts a specific immune response

artificially acquired passive immunotherapy

treatment in which patient receives via injection preformed antibodies in antitoxins or antisera, which can destroy fast-acting and potentially fatal antigens, such as rattlesnake venom