chapter 18 study guide Flashcards
Characteristics of Adaptive Immunity
specificity
memory
Targets specific pathogens.
Quickly responds to previously encountered pathogens.
Specificity:
Memory:
Mechanism of Specificity and Memory
programming of immune cells
primary and secondary
Enables rapid response to subsequent pathogen exposures.
programming of immune cells
Triggered by the first exposure to a pathogen or vaccine.
:
Faster and stronger due to immune memory.
Specific to the initial pathogen.
primary response
secondary response
cell types in adaptive immunity
b cells
t cells
Mature in bone marrow.
Produce glycoproteins (antibodies or immunoglobulins).
Defend against extracellular pathogens and toxins.
Mechanism: Humoral immunity (involves B cells and antibodies).
B cells
Mature in the thymus.
Act as central orchestrators of both innate and adaptive immune responses.
Destroy cells infected with intracellular pathogens.
Mechanism: Cell-mediated immunity (targeting and destruction of intracellular pathogens).
T cells
Trigger activation of adaptive immune defenses.
Unique to specific pathogens (e.g., varicella-zoster virus antigens differ from other viral pathogens).
Differ from PAMPs (found on numerous pathogens)
antigen
Found in capsules, cell walls, fimbriae, flagella, pili, toxins, and enzymes.
bacteria antigens
Associated with capsids, envelopes, and spike structures.
viral antigens
Effectiveness as antigens depends on structural complexity
proteins most effective
carbohydrates less effective
nucleic acids least effective
Smaller exposed regions on antigen surfaces recognized by antibodies or T cells.
epitopes
Small molecules (______):
Not antigenic alone.
Become antigenic when attached to larger carrier molecules (e.g., proteins).
haptens
cause specific immune responses, including allergic reactions:
Example:
Urushiol (poison ivy oil) causes contact dermatitis.
Penicillin can trigger allergic reactions to its drug class.
haptens
An ____ is a macromolecule that reacts with components of the immune system
antigen
Also called immunoglobulins.
Glycoproteins found in blood and tissue fluids
antibodies
Consists of four protein chains held together by disulfide bonds:
Disulfide bond: Covalent bond between sulfhydryl R groups of two cysteine amino acids.
Two identical heavy chains (largest).
Two identical light chains (smallest).
Forms a Y-shaped structure.
basic structure of antibody monomer
Arms of the Y-shaped antibody molecule.
Serves as the site of antigen binding.
FAB region
Neutralization of pathogens.
Agglutination or aggregation of pathogens.
Antibody-dependent cell-mediated cytotoxicity.
FAB region
Located in the trunk of the Y.
Site of complement factor binding.
Site of binding to phagocytic cells during antibody-mediated opsonization.
FC region
The _____ determines the class (isotype) of the antibody.
constant region
five classes of antibodies
IgG, IgM, IgA, IgD, IgE.
Penetrates tissue spaces efficiently.
Only antibody that crosses the placental barrier, providing passive immunity to the fetus.
Most versatile in defense against pathogens.
IgG
First antibody produced during primary and secondary immune responses.
Diagnostic marker for active/recent infections (pathogen-specific IgM).
Ten Fab sites enhance pathogen binding.
IgM
Most abundant in mucus secretions (protects mucous membranes).
Found in breast milk, tears, and saliva.
Traps pathogens in mucus for elimination.
IgA
Found on B cell surfaces as an antigen-binding receptor.
Function: Not secreted by B cells.
Trace amounts in serum result from degradation of old B cells
IgD
Involved in anti-parasitic defenses.
Fc region binds to basophils and mast cells.
Fab region binds antigen epitopes, triggering release of pro-inflammatory mediators.
Central to allergic reactions and inflammation defense mechanisms.
IgE
Antibodies involved: IgG, IgM, IgA.
Mechanism:
Antibodies bind to epitopes on the pathogen/toxin surface, preventing attachment to cells.
Neutralization
Neutralization of pathogens.
Opsonization for phagocytosis.
Agglutination (aggregation of pathogens).
Complement activation.
Antibody-dependent cell-mediated cytotoxicity.
Provide a link between adaptive specific immunity and innate nonspecific immunity.
Functions of antibodies
Secretory IgA: Blocks pathogens from attaching to intestinal mucosal cells.
Antibodies neutralize toxins by blocking their attachment to target cells.
Viruses are neutralized, preventing infection of cells.
neutralization
Pathogens are coated with molecules (e.g., complement factors, C-reactive protein, serum amyloid A) to assist phagocytosis.
IgG acts as an excellent opsonin by binding Fab sites to pathogen epitopes.
opsonization
Cross-linking of pathogens by antibodies creates large aggregates.
IgG:
Two Fab antigen-binding sites can bind two separate pathogens, clumping them together.
Large aggregates are easier for kidneys and spleen to filter from blood and easier for phagocytes to ingest.
IgM:
Pentameric structure provides ten Fab binding sites per molecule.
Most efficient antibody for ______.
Agglutination (Aggregation)
Three pathways, with the _____ being the most efficient.
requires:
Initial binding of IgG or IgM antibodies to the surface of a pathogen.
Recruitment and activation of the C1 complex.
classical pathway
____ is a collection of genes coding for___ molecules on the surface of all nucleated cells.
In humans, these genes are also called human leukocyte antigen (HLA) genes.
Mature red blood cells lack a nucleus and do not express ___ molecules
MHC
Found on all nucleated cells.
Presents:
Normal self-antigens.
Abnormal or nonself antigens (e.g., pathogens) to effector T cells for cellular immunity.
MHC 1
Found only on macrophages, dendritic cells, and B cells.
Presents:
Abnormal or nonself antigens for the initial activation of T cells.
MHC 2
Composed of:
A longer α protein chain.
A smaller β2 microglobulin protein.
Only the α chain spans the cytoplasmic membrane.
The α chain folds into three domains: α1, α2, and α3.
MHC 1
Two protein chains (α and β) of similar length.
Both chains span the plasma membrane.
Each chain folds into two domains:
α1 and α2 (α chain).
β1 and β2 (β chain).
MHC 2
Formed by α1 and α2 domains.
Formed by α1 and β1 domains.
MHC 1
MHC 2
All nucleated cells process and present antigens with MHC molecules to signal the immune system.
Macrophages, dendritic cells, and B cells specifically present antigens to activate T cells, making them ____.
antigen presenting cells APC
Function as phagocytes.
Ingest and kill pathogens that penetrate the skin or mucous membranes.
Recognize pathogens via nonspecific receptor interactions (e.g., PAMPs, toll-like receptors, complement, or antibody receptors).
Macrophages and dendritic cells
Do not function as phagocytes.
Use antigen-specific immunoglobulin receptors (monomeric IgD and IgM) to interact with foreign pathogens or free antigens.
Internalize antigens through endocytosis, then process and present them to T cells.
B cells
Found on all normal, healthy, nucleated cells.
Role of MHC I in Normal Cells:
Cross-presentation mechanisms are not fully understood but are mainly carried out by
dendritic cells
Originates from hematopoietic stem cells (HSCs) in the bone marrow.
Differentiates into lymphoid stem cells, then immature lymphocytes (lymphoblasts)
immature T cells travel via the bloodstream to the thymus for maturation
T cell production
98% of thymocytes are eliminated during thymic selection.
The remaining 2% mature and exit the thymus as
mature naive T cells
T cells are divided into
helper T cells, regulatory T cells, and cytotoxic T cells.
Central orchestrators of immune responses.
Activate and direct humoral and cellular immunity.
Enhance pathogen-killing functions of macrophages and natural killer (NK) cells.
helper T cells cd 4
Prevent undesirable or damaging immune responses.
Role in peripheral tolerance to protect against autoimmune diseases.
regulatory T cells cd 4
Effector cells for cellular immunity.
Recognize and destroy cells infected by intracellular pathogens.
Kill infected cells along with pathogens inside.
Cytotoxic T Cells (CD8+):
Long-lived and “remember” a specific antigen/epitope.
Provide a rapid and strong secondary response upon subsequent exposure.
memory helper T cells
____are derived from multipotent hematopoietic stem cells (HSCs) in the bone marrow.
Unlike T cells, ____ do not migrate to the thymus for maturation; they mature in the bone marrow.
B cells
Ensures B cells have functional antigen-binding receptors.
B cell maturation process
positive selection
Removes self-reactive B cells to prevent autoimmunity through:
Apoptosis (cell death).
Receptor editing/modification to eliminate self-reactivity.
Induction of anergy (Non responsiveness).
B cell maturation process
negative selection
Immature B cells that pass selection leave the bone marrow and travel to the ____ for final maturation.
spleen
Mature B cells in the spleen are referred to as
naive mature B cells
Individual’s own adaptive immune defenses are activated.
Adaptive immune defenses are transferred from another individual or animal
Active Immunity:
passive immunity
Develops after natural exposure to a pathogen.
Examples: Lifelong immunity after recovery from chickenpox or measles
Natural Active Immunity
Involves the natural transfer of antibodies from parent to child:
IgG: Crosses the placenta, providing passive immunity for up to 6 months after birth.
Secretory IgA: Transferred through breast milk.
natural passive immunity
Transfer of antibodies from a donor to another individual for:
Prophylaxis (e.g., rabies, hepatitis A/B, chickenpox in high-risk individuals).
Treatment of active infections (e.g., cytomegalovirus, Ebola).
Toxin-related diseases (e.g., tetanus, botulism, diphtheria).
Example: 1995 Ebola outbreak, where blood transfusions from recovered patients reduced mortality
artificial passive immunity
Deliberate exposure to weakened/inactivated pathogens or key pathogen antigens to activate immunity
vaccination
artificial active immunity
occurs when there are too few susceptible individuals in a population for a disease to spread effectively.
It protects susceptible individuals indirectly, even if they cannot mount their own immune response
herd immunity
benefits unvaccinated individuals if a critical percentage of the population is immune
herd immunity
