BIO202 PAST PAPER EXAM 2025 QUESTIONS WITH
ANSWERS RATED A+
✔✔Define adaptive (specific) immunity and discuss its properties of specificity and
memory. - ✔✔Specificity:
- Adaptive immunity distinguishes between numerous antigens (molecules that trigger
an immune response).
- It does so by utilizing specialized immune cells like B cells (which produce antibodies)
& T cells (which recognize & eliminate infected cells).
- These cells have unique receptors that can bind to specific parts of an antigen, called
epitopes.
- This allows for a tailored immune response specific to particular pathogen or antigen.
Memory:
- After an initial encounter with a pathogen, adaptive immunity develops memory cells
(memory B cells & memory T cells).
- These memory cells persist in body & can rapidly respond to subsequent exposures to
same antigen.
- This rapid & strong response is known as a secondary immune response, providing
long-lasting protection.
- Vaccinations leverage this memory to induce an immune response without causing
illness
✔✔Distinguish the difference between cell-mediated and antibody-mediated immunity
and which uses T cells and which uses B cells. Determine which is better against
intracellular pathogens and which is better against extracellular pathogens. - ✔✔Cell-
mediated immunity:
- Involves T cells, which are lymphocytes that mature in thymus.
- Recognizes & targets antigens on surface of infected cells, including viruses, certain
bacteria, & intracellular parasites.
- Cytotoxic T cells directly kill infected cells, while helper T cells help activate other
immune cells.
- Also plays a role in fighting cancer cells & rejecting transplanted organs.
- Cell-mediated immunity is more effective against intracellular pathogens because T
cells can directly interact with infected cells.
Antibody-mediated immunity (humoral immunity):
-Involves B cells, which mature in bone marrow. -B cells produce antibodies that bind to
specific antigens on surface of pathogens. -Antibodies can neutralize pathogens,
opsonize them for phagocytosis, & activate complement, a system that can destroy
pathogens. -Humoral immunity is more effective against extracellular pathogens & their
toxins because antibodies can circulate in blood & lymph & bind to pathogens before
they enter cells.
,✔✔What are the characteristics of antigens? - ✔✔1. Foreignness: must be recognized
as non-self by immune system to elicit response. This means they are typically from
external sources like pathogens, toxins, or allergens.
2. Immunogenicity: refers to antigen's ability to stimulate immune system to produce
antibodies & other immune cells that recognize & respond to it.
3. Reactivity: possess specific regions called epitopes or antigenic determinants that
antibodies can bind to. This binding triggers specific immune response.
4. Size & Composition: Most antigens are large, complex molecules with high molecular
weight, often proteins or polysaccharides. However, smaller molecules, like lipids or
peptides, can also act as antigens under certain conditions.
5. Specificity: are highly specific, meaning that antibodies produced against a specific
antigen will typically only bind to that specific antigen or closely related antigens.
6. Location: can be found on surface of cells, in cell secretions, or dissolved in bodily
fluids.
7. Types of Antigens: can be classified as exogenous (coming from outside body) or
endogenous (produced within body). They can also be categorized as tumor antigens,
autoantigens, or native antigens.
✔✔Describe the roles of the major histocompatibility complex (MHC) in foreign antigen
recognition and the type of cells in the body that possess the two different classes of
MHCs. - ✔✔MHC Function in Antigen Recognition:
1. Antigen Processing: When foreign antigens (like pathogens or tumor cells) enter
body, they are processed within cells, either through antigen processing pathways (for
intracellular antigens) or through antigen presentation pathways (for extracellular
antigens). This processing breaks down antigens into smaller peptide fragments. 2.
Peptide Binding: These peptide fragments then bind to MHC molecules within cell. 3.
Presentation to T cells: MHC-peptide complex is then transported to cell surface, where
it is presented to T cells via T cell receptors (TCRs). 4. T cell Activation: If presented
peptide is recognized by T cell as foreign, T cell is activated, leading to an immune
response, such as cell-mediated immunity (MHC class I) or antibody production (MHC
class II). MHC Classes & Their Roles:
-MHC Class I:
-Found on all nucleated cells. -Presents peptides from intracellular pathogens (like
viruses) or tumor cells to cytotoxic T cells. -CD8+ T cells, which are responsible for
killing infected or cancerous cells, recognize MHC class I-peptide complex. -MHC Class
II:
-Found primarily on antigen-presenting cells (APCs), including dendritic cells,
macrophages, & B cells. -Presents peptides from extracellular pathogens (like bacteria)
to helper T cells. -CD4+ T cells, which help coordinate immune response, recognize
MHC class II-peptide complex.
✔✔What is needed to achieve co-stimulation of a T or B cell? - ✔✔T Cell Co-
stimulation:
-Signal 1: TCR & MHC Interaction: T cell receptor (TCR) on a T cell recognizes & binds
to a peptide presented by a MHC molecule on an antigen-presenting cell (APC). -Signal
2: Co-stimulatory Molecule Interaction: This signal reinforces activation & is crucial for
, full T cell activation. A common example is binding of CD28 on T cell to B7 molecules
on APC. Other co-stimulatory pathways also exist.
B Cell Co-stimulation:
-Signal 1: BCR & Antigen Interaction: B cell receptor (BCR) on a B cell recognizes &
binds to specific antigen. -Signal 2: Co-stimulatory Signal:
- T cell-dependent activation: B cells can be activated by helper T cells, which provide
co-stimulatory signals through interactions with CD40 on the B cell. - T cell-independent
activation: In some cases, B cells can be activated by signals directly from microbial
constituents. - Complement receptors: B cells can also receive costimulatory signals via
complement receptors.
✔✔Which T cell displays CD4 and which displays CD8 and which will be stimulated
best by intracellular pathogens and which by extracellular pathogens? - ✔✔CD4 T cells
(Helper T cells):
These cells express CD4 molecule on their surface, which interacts with MHC class II
molecules. MHC class II molecules are primarily found on antigen-presenting cells
(APCs) like dendritic cells, & they present peptides from extracellular pathogens or
pathogens that are phagocytosed by cell. CD4 T cells help activate other immune cells,
such as B cells & cytotoxic T cells, & they also play a role in regulating immune
response.
CD8 T cells (Cytotoxic T cells):
These cells express CD8 molecule on their surface, which interacts with MHC class I
molecules. MHC class I molecules are found on all nucleated cells in body, & they
present peptides from intracellular pathogens or from cells infected with intracellular
pathogens. Cytotoxic T cells directly kill infected or altered cells, helping to control
infections & remove damaged cells.
✔✔Describe the mechanisms used by cytotoxic T cells to destroy body cells that have
been invaded by pathogens. - ✔✔Mechanism 1: Perforin and Granzymes
1. Target Cell Recognition: CTLs recognize infected cells expressing foreign peptides
on their surface, bound to MHC class I molecules. 2. Perforin Release: Upon binding,
CTLs release perforin, which forms transmembrane pores in target cell membrane. 3.
Granzyme Entry: Granzymes, serine proteases, enter target cell through perforin pores.
4. Apoptosis Induction: Granzymes activate caspases, initiating cascade of enzymatic
reactions that leads to apoptosis. Mechanism 2: Fas Ligand
1. Fas Ligand Expression: CTLs express Fas ligand on their surface.
2. Fas Binding: Fas ligand binds to Fas, a death receptor, on target cell.
3. Apoptosis Activation: This binding triggers an apoptotic pathway, leading to cell
death.
✔✔What is an antibody? Describe the five functional classes of antibodies and know
that plasma cells from B cells make them. - ✔✔Antibody Structure: are Y-shaped
proteins composed of 2 heavy chains & 2 light chains. "arms" of Y bind to specific
antigens, while "stem" interacts with other immune cells.
ANSWERS RATED A+
✔✔Define adaptive (specific) immunity and discuss its properties of specificity and
memory. - ✔✔Specificity:
- Adaptive immunity distinguishes between numerous antigens (molecules that trigger
an immune response).
- It does so by utilizing specialized immune cells like B cells (which produce antibodies)
& T cells (which recognize & eliminate infected cells).
- These cells have unique receptors that can bind to specific parts of an antigen, called
epitopes.
- This allows for a tailored immune response specific to particular pathogen or antigen.
Memory:
- After an initial encounter with a pathogen, adaptive immunity develops memory cells
(memory B cells & memory T cells).
- These memory cells persist in body & can rapidly respond to subsequent exposures to
same antigen.
- This rapid & strong response is known as a secondary immune response, providing
long-lasting protection.
- Vaccinations leverage this memory to induce an immune response without causing
illness
✔✔Distinguish the difference between cell-mediated and antibody-mediated immunity
and which uses T cells and which uses B cells. Determine which is better against
intracellular pathogens and which is better against extracellular pathogens. - ✔✔Cell-
mediated immunity:
- Involves T cells, which are lymphocytes that mature in thymus.
- Recognizes & targets antigens on surface of infected cells, including viruses, certain
bacteria, & intracellular parasites.
- Cytotoxic T cells directly kill infected cells, while helper T cells help activate other
immune cells.
- Also plays a role in fighting cancer cells & rejecting transplanted organs.
- Cell-mediated immunity is more effective against intracellular pathogens because T
cells can directly interact with infected cells.
Antibody-mediated immunity (humoral immunity):
-Involves B cells, which mature in bone marrow. -B cells produce antibodies that bind to
specific antigens on surface of pathogens. -Antibodies can neutralize pathogens,
opsonize them for phagocytosis, & activate complement, a system that can destroy
pathogens. -Humoral immunity is more effective against extracellular pathogens & their
toxins because antibodies can circulate in blood & lymph & bind to pathogens before
they enter cells.
,✔✔What are the characteristics of antigens? - ✔✔1. Foreignness: must be recognized
as non-self by immune system to elicit response. This means they are typically from
external sources like pathogens, toxins, or allergens.
2. Immunogenicity: refers to antigen's ability to stimulate immune system to produce
antibodies & other immune cells that recognize & respond to it.
3. Reactivity: possess specific regions called epitopes or antigenic determinants that
antibodies can bind to. This binding triggers specific immune response.
4. Size & Composition: Most antigens are large, complex molecules with high molecular
weight, often proteins or polysaccharides. However, smaller molecules, like lipids or
peptides, can also act as antigens under certain conditions.
5. Specificity: are highly specific, meaning that antibodies produced against a specific
antigen will typically only bind to that specific antigen or closely related antigens.
6. Location: can be found on surface of cells, in cell secretions, or dissolved in bodily
fluids.
7. Types of Antigens: can be classified as exogenous (coming from outside body) or
endogenous (produced within body). They can also be categorized as tumor antigens,
autoantigens, or native antigens.
✔✔Describe the roles of the major histocompatibility complex (MHC) in foreign antigen
recognition and the type of cells in the body that possess the two different classes of
MHCs. - ✔✔MHC Function in Antigen Recognition:
1. Antigen Processing: When foreign antigens (like pathogens or tumor cells) enter
body, they are processed within cells, either through antigen processing pathways (for
intracellular antigens) or through antigen presentation pathways (for extracellular
antigens). This processing breaks down antigens into smaller peptide fragments. 2.
Peptide Binding: These peptide fragments then bind to MHC molecules within cell. 3.
Presentation to T cells: MHC-peptide complex is then transported to cell surface, where
it is presented to T cells via T cell receptors (TCRs). 4. T cell Activation: If presented
peptide is recognized by T cell as foreign, T cell is activated, leading to an immune
response, such as cell-mediated immunity (MHC class I) or antibody production (MHC
class II). MHC Classes & Their Roles:
-MHC Class I:
-Found on all nucleated cells. -Presents peptides from intracellular pathogens (like
viruses) or tumor cells to cytotoxic T cells. -CD8+ T cells, which are responsible for
killing infected or cancerous cells, recognize MHC class I-peptide complex. -MHC Class
II:
-Found primarily on antigen-presenting cells (APCs), including dendritic cells,
macrophages, & B cells. -Presents peptides from extracellular pathogens (like bacteria)
to helper T cells. -CD4+ T cells, which help coordinate immune response, recognize
MHC class II-peptide complex.
✔✔What is needed to achieve co-stimulation of a T or B cell? - ✔✔T Cell Co-
stimulation:
-Signal 1: TCR & MHC Interaction: T cell receptor (TCR) on a T cell recognizes & binds
to a peptide presented by a MHC molecule on an antigen-presenting cell (APC). -Signal
2: Co-stimulatory Molecule Interaction: This signal reinforces activation & is crucial for
, full T cell activation. A common example is binding of CD28 on T cell to B7 molecules
on APC. Other co-stimulatory pathways also exist.
B Cell Co-stimulation:
-Signal 1: BCR & Antigen Interaction: B cell receptor (BCR) on a B cell recognizes &
binds to specific antigen. -Signal 2: Co-stimulatory Signal:
- T cell-dependent activation: B cells can be activated by helper T cells, which provide
co-stimulatory signals through interactions with CD40 on the B cell. - T cell-independent
activation: In some cases, B cells can be activated by signals directly from microbial
constituents. - Complement receptors: B cells can also receive costimulatory signals via
complement receptors.
✔✔Which T cell displays CD4 and which displays CD8 and which will be stimulated
best by intracellular pathogens and which by extracellular pathogens? - ✔✔CD4 T cells
(Helper T cells):
These cells express CD4 molecule on their surface, which interacts with MHC class II
molecules. MHC class II molecules are primarily found on antigen-presenting cells
(APCs) like dendritic cells, & they present peptides from extracellular pathogens or
pathogens that are phagocytosed by cell. CD4 T cells help activate other immune cells,
such as B cells & cytotoxic T cells, & they also play a role in regulating immune
response.
CD8 T cells (Cytotoxic T cells):
These cells express CD8 molecule on their surface, which interacts with MHC class I
molecules. MHC class I molecules are found on all nucleated cells in body, & they
present peptides from intracellular pathogens or from cells infected with intracellular
pathogens. Cytotoxic T cells directly kill infected or altered cells, helping to control
infections & remove damaged cells.
✔✔Describe the mechanisms used by cytotoxic T cells to destroy body cells that have
been invaded by pathogens. - ✔✔Mechanism 1: Perforin and Granzymes
1. Target Cell Recognition: CTLs recognize infected cells expressing foreign peptides
on their surface, bound to MHC class I molecules. 2. Perforin Release: Upon binding,
CTLs release perforin, which forms transmembrane pores in target cell membrane. 3.
Granzyme Entry: Granzymes, serine proteases, enter target cell through perforin pores.
4. Apoptosis Induction: Granzymes activate caspases, initiating cascade of enzymatic
reactions that leads to apoptosis. Mechanism 2: Fas Ligand
1. Fas Ligand Expression: CTLs express Fas ligand on their surface.
2. Fas Binding: Fas ligand binds to Fas, a death receptor, on target cell.
3. Apoptosis Activation: This binding triggers an apoptotic pathway, leading to cell
death.
✔✔What is an antibody? Describe the five functional classes of antibodies and know
that plasma cells from B cells make them. - ✔✔Antibody Structure: are Y-shaped
proteins composed of 2 heavy chains & 2 light chains. "arms" of Y bind to specific
antigens, while "stem" interacts with other immune cells.
