Antigens, Complement System, Humoral Immunity Flashcards
Which of the following is NOT a secondary signal involved in B cell activation?
a) Cytokine secretion by helper T cells
b) Direct binding of antigen to B cell MHC molecules
c) Complement system activation through the classical pathway
d) Signaling from toll-like receptors (TLRs) on B cells
Direct binding of antigen to B cell MHC molecules
What are T-independent antigens?
Antigens that can activate B cells without T cell help
Which antibody class is the most abundant in serum and plays a major role in secondary immune responses?
IgG
Which antibody class is primarily involved in mucosal immunity and is found in secretions like saliva and tears?
IgA
Which antibody class is responsible for mediating allergic reactions and immunity to parasites?
IgE
Which of the following is NOT a function of antibodies?
a) Neutralization of microbes and toxins
b) Opsonization to enhance phagocytosis
c) Direct lysis of infected cells
d) Activation of complement system
Direct lysis of infected cells
What is the term for the strength of the reaction between a single antigenic determinant and a single antibody combining site?
Affinity
What is the term for the overall strength of binding between a multivalent antigen and multivalent antibodies?
Avidity
What is cross-reactivity in the context of antigen-antibody interactions?
The ability of an antibody to bind to multiple different antigens
Which of the following factors does NOT influence antigen-antibody reactions?
a) Affinity of the antibody for the antigen
b) Avidity of the interaction
c) Temperature of the reaction
d) Physical form of the antigen
Temperature of the reaction
What is the primary function of plasma cells?
To secrete antibodies
What is the main characteristic of memory cells?
a) They are short-lived and die after the primary immune response.
b) They are low-affinity B cells that require T cell help.
c) They are high-affinity B cells that survive and provide a rapid response upon re-exposure to the same antigen.
d) They are responsible for initiating the primary immune response.
They are high-affinity B cells that survive and provide a rapid response upon re-exposure to the same antigen.
Which of the following statements about T-independent antigens is FALSE?
a) They can activate B cells without T cell help.
b) They typically induce IgM responses.
c) They generate memory cells.
d) Examples include bacterial lipopolysaccharide and flagellin.
They generate memory cells.
Which part of the antibody molecule is responsible for antigen binding?
Variable region
Which of the following is NOT a mechanism of antibody neutralization?
a) Blocking the binding of microbes to cells
b) Inhibiting the spread of microbes between cells
c) Directly killing infected cells
d) Blocking the binding of toxins to cells
Directly killing infected cells
How do antibodies facilitate opsonization?
By binding to microbes and being recognized by Fc receptors on phagocytes
Which antibody class is the largest and is primarily found in the circulation?
IgM
Which antibody class is the first to be produced during a primary immune response?
IgM
Which of the following statements about the antigen-antibody reaction is FALSE?
a) It is specific, meaning an antibody typically binds to a specific antigen.
b) It is irreversible, meaning the antibody and antigen remain permanently bound.
c) It is influenced by factors like affinity and avidity.
d) It can be detected through various methods depending on the physical form of the antigen.
It is irreversible, meaning the antibody and antigen remain permanently bound.
Which of the following is NOT a primary function of the complement system?
a) Lysis of pathogens
b) Opsonization of antigens
c) Antigen processing and presentation
d) Inflammation and chemotaxis
Antigen processing and presentation
What is the term for the inactive enzyme precursors found in the complement system?
Zymogens
Which organ is the main site of complement protein production?
Liver
Which complement pathway is initiated by the binding of C1q to a pathogen or antigen-antibody complex?
Classical pathway
Which complement pathway is triggered by bacterial endotoxin?
Alternative pathway
What is the key enzyme that is generated in all three complement pathways?
C3 convertase
Which complement protein is responsible for opsonization?
C3b
What is the membrane attack complex (MAC)?
A complex of complement proteins that forms a pore in the pathogen’s membrane
Which complement proteins act as chemoattractants?
a) C3a and C5a
b) C3b and C5b
c) C1q and MBL
d) MASP and C2
C3a and C5a
Which complement proteins are responsible for inflammation?
C3a, C4a, and C5a
Which type of bacteria are NOT susceptible to lysis by the complement system?
Gram-positive bacteria
What is the role of mannose-binding lectin (MBL) in complement activation?
It binds to mannose-containing carbohydrates on the pathogen surface.
What is the significance of the cascade nature of the complement system?
It amplifies the response, leading to rapid and effective elimination of pathogens.
Which of the following statements about the classical pathway is FALSE?
a) It is triggered by antigen-antibody complexes.
b) It involves the binding of C1q to the pathogen surface.
c) It is only involved in the adaptive immune response.
d) It leads to the generation of C3 convertase.
It is only involved in the adaptive immune response.
Which of the following statements about the alternative pathway is FALSE?
a) It is triggered by bacterial endotoxin.
b) It involves spontaneous hydrolysis of C3.
c) It requires prior antibody binding.
d) It leads to the generation of C3 convertase.
It requires prior antibody binding.
How does opsonization enhance the immune response?
By promoting phagocytosis of pathogens
Why is the rapid activation of complement important?
To keep pace with the rapid replication of pathogens
Which of the following is a potential consequence of complement deficiency?
a) Increased susceptibility to infections
b) Autoimmune diseases
c) Both a and b
d) Neither a nor b
Both a and b
What is an epitope?
A specific region on an antigen that binds to immune receptors
What is a hapten?
A small molecule that becomes immunogenic when attached to a larger carrier molecule
Which of the following is an example of a hapten?
a) Penicillin
b) Lipopolysaccharide
c) Peptidoglycan
d) Viral capsid protein
Penicillin
What is a cross-reaction in immunology?
The reaction between an antibody and multiple different antigens
Which of the following is NOT a microbial antigen?
a) Blood group antigens
b) Bacterial lipopolysaccharide
c) Viral capsid proteins
d) Fungal cell wall components
Blood group antigens
Which of the following is an example of a non-microbial antigen?
a) Peptidoglycan
b) Histocompatibility antigens
c) Viral envelope proteins
d) Parasitic proteins
Histocompatibility antigens
What is the function of ubiquitin in antigen processing?
To tag proteins for destruction by proteasomes
What is the role of proteasomes in antigen processing?
To degrade ubiquitin-tagged proteins
Which MHC class pathway is involved in the presentation of endogenous antigens?
MHC class I pathway
Which type of T cell recognizes antigens presented by MHC class I molecules?
Cytotoxic T cells
Which MHC class pathway is involved in the presentation of exogenous antigens?
MHC class II pathway
Which type of T cell recognizes antigens presented by MHC class II molecules?
Helper T cells
Which of the following is NOT a characteristic of dendritic cells (DCs)?
a) They are highly efficient antigen-presenting cells.
b) They can activate both naïve and memory T cells.
c) They are primarily involved in presenting endogenous antigens.
d) They can be found in various locations, including skin and lymph nodes.
They are primarily involved in presenting endogenous antigens.
Which of the following is NOT a function of macrophages in antigen presentation?
a) To engulf and digest exogenous antigens
b) To present antigens to T cells
c) To activate naïve T cells
d) To secrete cytokines
To activate naïve T cells
Which of the following statements about B cells in antigen presentation is FALSE?
a) They can internalize and process antigens.
b) They present antigens to helper T cells.
c) They express MHC class II molecules.
d) They are the most efficient antigen-presenting cells.
They are the most efficient antigen-presenting cells.
Which of the following cells is NOT considered a “professional” antigen-presenting cell?
a) Dendritic cells
b) Macrophages
c) B cells
d) Neutrophils
Neutrophils
What is MHC restriction?
The requirement for antigens to be presented by MHC molecules to activate T cells
What is the role of the transporter protein (TAP) in antigen processing?
To transport peptides into the endoplasmic reticulum
Which of the following statements about antigen processing is FALSE?
a) It is necessary for the activation of adaptive immunity.
b) It involves the breakdown of antigens into smaller fragments.
c) It requires the involvement of MHC molecules.
d) It occurs only for exogenous antigens.
It occurs only for exogenous antigens.
Enumerate the 4 properties of a good antigen
Foreign
Large (> 1000 DA)
Complex
Stability
These are far too small molecules to be appropriately processed and presented to the immune system therefore are not immunogenic
Haptens
Enumerate the 4 factors that influence Ag-Ab reaction
- Affinity
- Avidity
- Antigen-antibody ratio
- Physical form of the antigen
Enumerate the 3 properties of Ag-Ab reaction
- Lock and Key concept
- Non-covalent bonding
- Reversible
It refers to the ability of an individual antibody combining site to react with more than one antigenic determinant
Cross-reactivity
Known as the measure of the overall strength of binding of an antigen with many antigenic determinants and multivalent antibodies
Avidity
Defined as the strength of the reaction
between a single antigenic determinant and a single combining site on the antibody
Affinity
The non-covalent biochemical reaction between antigen and antibody
Specific and reversible
It refers to the ability of an individual antibody combining site to react with only one antigenic determinant
Specificity
Described as reactions between multivalent antigens and multivalent antibodies are more stable, it is easier to detect.
Avidity
What term describes the strength of a single antigen-antibody binding interaction, where a higher value indicates a more stable complex?
Affinity
What principle explains why reactions involving multiple binding sites on both antigens and antibodies result in stronger, more easily detectable interactions?
Avidity
What factor, determined by the relative amounts of reactants, affects the size and detectability of antigen-antibody complexes?
Antigen-antibody ratio
What characteristic of an antigen dictates whether one observes agglutination or precipitation when it reacts with its corresponding antibody?
Physical form of the antigen
What concept describes the specific interaction between an antibody’s binding site and an antigen’s determinant, where one fits precisely into the other?
Lock and key
What type of chemical bonding primarily facilitates the interaction between antigens and antibodies, allowing for a relatively weak, yet numerous, interaction?
Non-covalent bonding
What characteristic of antigen-antibody reactions is attributed to the nature of the bonds involved, allowing the complex to dissociate?
Reversible
