Adaptive Immunity

Question 1

What are the two main types of adaptive immunity?

Answer 1

humoral immunity, cell-mediated immunity

Question 2

What are four key features of adaptive immunity?

Answer 2

(a) specificity
(b) memory
(c) adaptive/diversity [The adaptive immune system can recognize and respond to a vast array of different antigens.]
(d) self/non-self recognition

Question 3

“The acquired immune response is mediated by lymphocytes which come in two major varieties, T-lymphocytes and B-lymphocytes.” What are two key features of these cells that set them apart from the cells of the innate immune system?

Answer 3

(a) they are highly antigen specific
(b) they exhibit immunological memory whereby they respond more vigorously upon re-encounter with a specific antigen

Question 4

List the phases of the humoral immune response.

Answer 4

(1) Antigen recognition
(2) Activation of B cells
(3) Proliferation and differentiation
(4) Plasma cell formation
(5) Antibody production
(6) Memory cell generation
(7) Secondary response
[Diagram 1] [Diagram 2]

Question 5

Recognition molecules of the adaptive immune system

(a) What is the B cell receptor (BCR)?
(b) What is the function of the B cell receptor?

Answer 5

(a) A membrane-bound form of immunoglobulin found on the surface of B cells.
(b) It allows B cells to recognize and bind to specific antigens, triggering B cell activation and proliferation.

Question 6

Recognition molecules of the adaptive immune system

(a) What are immunoglobulins (Ig)?
(b) What is the structure of immunoglobulins?
(c) What are the types of immunoglobulins?

Answer 6

(a) Glycoproteins produced by B cells that recognize and bind to specific antigens.
(b) Immunoglobulins are composed of two heavy chains and two light chains, forming a Y-shaped molecule. [Diagram 1] [Diagram 2]
(c) IgG, IgA, IgM, IgE, IgD [Diagram 3]

Question 7

Recognition molecules of the adaptive immune system

What are the two main [functional] parts of an immunoglobulin?

Answer 7

(1) The variable region (Fab region): This region is responsible for binding to specific antigens. The variable region’s structure varies greatly between different antibodies, allowing each antibody to recognize a unique antigen.
[Structure: It is composed of the tips of the Y-shaped antibody, including parts of both the heavy and light chains.]

(2) The constant region (Fc region): This region mediates the immune response by interacting with other components of the immune system, such as phagocytes and complement proteins.
[Structure: It forms the stem of the Y-shaped antibody and is relatively constant among antibodies of the same class.]

Question 8

Explain clonal selection and expansion.

Answer 8

Clonal selection is the process by which an antigen selectively binds to and activates specific lymphocytes that have receptors matching that antigen.
Clonal expansion refers to the subsequent proliferation of the activated lymphocyte, producing many identical daughter cells.

Question 9

What are the main components of T-cell receptors (TCRs)?

Answer 9

TCRs are typically composed of two different protein chains. In most T cells, these are the alpha (α) and beta (β) chains. A smaller subset of T cells has gamma (γ) and delta (δ) chains.
[Diagram 1] [Diagram 2] [Diagram 3]

Question 10

What are the regions of each TCR chain?

Answer 10

Each chain has a variable region that binds to antigens and a constant region that anchors the receptor to the cell membrane.
[Diagram 1] [Diagram 2] [Diagram 3]

Question 11

How do TCRs recognize antigens?

Answer 11

TCRs recognize fragments of antigens presented by major histocompatibility complex (MHC) molecules on the surface of other cells.

Question 12

What happens when a TCR binds to an antigen-MHC complex?

Answer 12

When a TCR binds to an antigen-MHC complex, it triggers a series of biochemical events inside the T cell, leading to its activation. This can result in the T cell attacking infected cells or helping other immune cells respond more effectively.

Question 13

What are the two main types of T cells?

Answer 13

(a) CD4+ Helper T Cells
(b) CD8+ Cytotoxic T Cells

Question 14

What is the role of CD4+ Helper T Cells?

Answer 14

CD4+ Helper T Cells coordinate the immune response by signaling other cells, such as B cells and cytotoxic T cells, to perform their functions.

Question 15

What is the role of CD8+ Cytotoxic T Cells?

Answer 15

CD8+ Cytotoxic T Cells directly attack and destroy infected or cancerous cells.

Question 16

(a) What is the function of antigen-presenting cells (APCs)?
(b) What are primary types of antigen presenting cells?

Answer 16

(a) APCs capture, process and present antigens to T cells, initiating an immune response.
(b) Dendritic cells, macrophages, and B cells

Question 17

(a) What is Major Histocompatibility Complex?
(b) What are the two mian classes of MHC molecules?

Answer 17

(a) The Major Histocompatibility Complex is a set of genes that play a crucial role in the immune system’s ability to recognize and respond to foreign substances.

(b) Classes of MHC molecules:
(1) MHC Class I: Found on almost all nucleated cells, these molecules present peptides to cytotoxic T cells, which destroy infected or cancerous cells.

(2) MHC Class II: Found on specialized antigen-presenting cells like macrophages and dendritic cells, these molecules present peptides to helper T cells, which then activate other immune cells to respond to the threat.

Question 18

Outline the mechanism of Antibody-dependent cell-mediated cytotoxicity (ADCC).

Answer 18

☑ When a pathogen (like a virus-infected cell) is present, antibodies produced by B-cells bind to specific antigens.
☑ Effector cells of the immune system, such as natural killer cells, macrophages, neutrophils and eosinophils recognize and bind to the Fc region of these antibodies via their Fc receptors.
☑ Once bound, these effector cells release cytotoxic substances like perforin and granzymes, which lead to the destruction of the target cell.

Question 19

Which of the following cells is the main effector of cell mediated immunity against intracellular pathogens?
(a) Neutrophils
(b) Plasma cells
(c) B cells
(d) Cytotoxic T cells
(e) Basophils

Answer 19

(d) Cytotoxic T cells