3.2.4 Cell recognition and immunity

Question 1

What is an antigen?

Answer 1

A molecule, usually a protein, that triggers an immune response when recognized as foreign by the immune system.

Question 2

What is the role of antigens in the immune response?

Answer 2

Antigens are used by the immune system to identify pathogens, abnormal body cells, toxins, and non-self material (e.g., cells from other organisms).

Question 3

What are the main types of white blood cells involved in the immune response?

Answer 3

Phagocytes: Engulf and digest pathogens.

T lymphocytes (T cells): Involved in cell-mediated immunity.

B lymphocytes (B cells): Involved in humoral immunity by producing antibodies.

Question 4

What are self and non-self cells?

Answer 4

Self cells are the body’s own cells, while non-self cells are foreign and trigger an immune response.

Question 5

What is the difference between specific and non-specific immune responses?

Answer 5

Non-specific: Immediate and general defense (e.g., phagocytosis, inflammation).

Specific: Slower but targets specific antigens (e.g., T and B cells).

Question 6

Describe the role of lysosomes in the immune response.

Answer 6

Lysosomes contain enzymes (e.g., lysozymes) that digest pathogens after phagocytosis.

Question 7

What is the role of inflammation in the non-specific immune response?

Answer 7

Inflammation increases blood flow to the affected area, bringing more white blood cells and antimicrobial proteins to fight infection.

Question 8

What is phagocytosis?

Answer 8

The process where phagocytes engulf and digest pathogens.

Question 9

Describe the stages of phagocytosis.

Answer 9

Pathogen is recognized and binds to receptors on the phagocyte.

The pathogen is engulfed into a vesicle called a phagosome.

The phagosome fuses with a lysosome to form a phagolysosome.

Enzymes digest the pathogen.

The phagocyte presents the pathogen’s antigens on its surface (antigen presentation).

Question 10

What are T cells, and where are they produced?

Answer 10

T cells are lymphocytes involved in the cell-mediated immune response. They are produced in the bone marrow and mature in the thymus.

Question 11

What is the role of helper T cells (TH cells)?

Answer 11

Helper T cells:

Release cytokines to activate B cells, cytotoxic T cells, and phagocytes.

Stimulate clonal expansion of B and T cells.

Question 12

What is the role of cytotoxic T cells (TC cells)?

Answer 12

Destroy infected cells by releasing perforins, which create pores in the cell membrane, causing cell lysis.

Question 13

What is the process of clonal selection and clonal expansion?

Answer 13

Clonal selection involves identifying the specific lymphocyte that matches the antigen. Clonal expansion is the rapid mitotic division of this lymphocyte to produce a large population of identical cells.

Question 14

What are B cells, and where are they produced?

Answer 14

B cells are lymphocytes involved in the humoral immune response. They are produced and mature in the bone marrow.

Question 15

What is the role of plasma cells?

Answer 15

Plasma cells are activated B cells that secrete specific antibodies to fight pathogens.

Question 16

What are memory cells, and why are they important?

Answer 16

Memory cells are long-lived B or T cells that remain after an infection, allowing a faster and stronger secondary immune response if the same antigen is encountered again.

Question 17

What are the four main ways antibodies work?

Answer 17

Agglutination: Clumping pathogens together for easier phagocytosis.

Neutralization: Blocking toxins or preventing pathogens from binding to cells.

Opsonization: Marking pathogens for phagocytosis.

Activation of complement: Triggering a cascade that leads to pathogen lysis.

Question 18

What is the difference between the primary and secondary immune responses?

Answer 18

Primary response: Slow and produces fewer antibodies; occurs during the first exposure to an antigen.

Secondary response: Faster and stronger due to memory cells.

Question 19

What is a vaccine, and how does it work?

Answer 19

A vaccine contains antigens from a pathogen (weakened or inactivated) that stimulate the production of memory cells without causing disease.

Question 20

What is the difference between active and passive immunity?

Answer 20

Active immunity: Produced by the individual’s immune system (e.g., vaccination or natural infection).

Passive immunity: Antibodies are provided from an external source (e.g., maternal antibodies or antibody injection).

Question 21

What are the advantages and disadvantages of active and passive immunity?

Answer 21

Active immunity: Long-lasting but slower to develop.

Passive immunity: Immediate but short-term.

Question 22

What are monoclonal antibodies?

Answer 22

Identical antibodies produced from a single B cell clone, specific to one antigen.

Question 23

Give two uses of monoclonal antibodies in medicine.

Answer 23

Cancer treatment: Delivering drugs to specific cancer cells.

Diagnostic tests: Detecting specific antigens (e.g., in pregnancy tests).

Question 24

What are the ethical issues surrounding monoclonal antibody use?

Answer 24

Use of animals in antibody production, potential side effects, and accessibility concerns.

Question 25

What is antigenic variability, and how does it affect immunity?

Answer 25

Antigenic variability occurs when pathogens change their surface antigens. It makes them harder to recognize, leading to recurring infections and reducing vaccine effectiveness (e.g., flu virus).

Question 26

Why is antigenic variability common in RNA viruses?

Answer 26

RNA viruses lack proofreading enzymes during replication, leading to frequent mutations.

Question 27

What is an autoimmune disease?

Answer 27

A condition where the immune system mistakenly attacks the body’s own cells (e.g., rheumatoid arthritis, type 1 diabetes).

Question 28

How do autoimmune diseases arise?

Answer 28

failure of self-recognition mechanisms, leading to an immune response against self-antigens.

Question 29

How can you test for the presence of a specific antigen in a sample?

Answer 29

Using the ELISA test (enzyme-linked immunosorbent assay).

Question 30

Describe the steps of an ELISA test.

Answer 30

Antigen is bound to a surface.

Add specific antibodies that bind to the antigen.

Add a second antibody with an enzyme attached.

Add substrate for the enzyme, causing a color change if antigen is present.

Question 31

What is the importance of controls in an ELISA test?

Answer 31

To ensure the results are valid by confirming that the observed effects are due to the antigen-antibody reaction.

Question 32

What does a graph of antibody concentration vs. time show during primary and secondary immune responses?

Answer 32

The secondary response shows a faster and larger increase in antibody concentration compared to the primary response

Question 33

How can data from vaccination programs be used to evaluate effectiveness?

Answer 33

By comparing infection rates before and after the introduction of a vaccine and analyzing herd immunity effects.

Question 34

What does the term “herd immunity” mean?

Answer 34

When a large proportion of the population is immune, reducing the spread of a pathogen and protecting individuals who are not immune.