Module 3.2 Adaptive Immunity

Question 1

Describe humoral immunity

Answer 1

• Involves the production and use of antibodies that bind to antigens on infectious agents by b-cells
• Antibodies can directly inactivate a microorganism or active a variety of inflammatory mediators (complement, phagocytes) that will destroy the pathogen.

Question 2

Describe cell-mediated immunity

Answer 2

• Involves T-cells directly reacting with antigens on the surface of infectious agents.
• They can stimulate activities of other leukocytes via cell-to-cell contact or through secretion of cytokines.

Question 3

What is active immunity?

Answer 3

• It is produced by an individual either after natural exposure to an antigen or after immunization.
• Long-lasting, but requires time (1-2 weeks) to develop

Question 4

What is passive immunity?

Answer 4

• It is performed by antibodies or T-lymphocytes that are transferred to a recipient to produce immunity, rapidly developed, but are temporary, e.g. immune globulin administration.
• This can occur naturally as in the passage of maternal antibodies to the fetus.
• Or it can occur artificially as in a clinic using immunotherapy for a specific disease.

Question 5

What are antigens and describe their role in adaptive immunity

Answer 5

• It is a molecule that can react with antibodies or antigen receptors on B & T-cells
• Most are also immunogens - capable of inducing an immune response, resulting in the production of antibodies or functional t-cells
• To function as an antigen, at least a portion of a molecules chemical structure must be recognized by and bound to an antibody or to specific receptors on a lymphocyte.

Question 6

What are antibodies?

Answer 6

• Also known as immunoglobulins, are serum glycoproteins produced by plasma cells (b-cells) in response to a challenge by an immunogen and are specific to that antigen.

Question 7

Describe the 4 main types of immunoglobulins and their functions

Answer 7

• IgG - Most abundant, consisting of 80-85% of the immunoglobulins circulating in the body and account for most of the protective activity against infections
• IgA - Are found in normal body secretions
• IgM - It is the first antibody produced during the initial or primary response to an antigen
• IgE - It appears to function as a mediator of many common allergic responses and in the defense against parasitic infections.

Question 8

How do antibodies fight pathogens?

Answer 8

1. neutralize bacterial toxins
2. neutralizing viruses
3. opsonizing bacteria (promoting phagocytosis)
4. activating components of the inflammatory response.
5. Direct actions of antibodies:
   
   • Agglutination - cause the organisms to clump together.
   • Precipitation - cause the organism to fall out of solution.
   • Neutralization - inactivate the organism.

Question 9

Describe the role of cytokines and their role in the immune response

Answer 9

• A large number of cytokines are secreted by APCs and lymphocytes and provide both positive and negative regulation of the immune response.
• Lymphocytes respond to cytokines by:
  
  • ↑ing the production of proteins, many of which are other cytokines or cytokine receptors.
  • Can cause a lymphocyte proliferation and differentiation

Question 10

What are antigen presenting cells and describe their role in the adaptive immunity?

Answer 10

• Many cells have the capacity to present antigens to T & B lymphocytes, but dendritic cells, macrophages, and B lymphocytes are very efficient at macrophage presentation.
• B-cells present antigens to Th cells that facilitate development of the humoral immune response
• Macrophages are very effective in presenting antigens to memory Th cells in order to initiate a rapid response to antigens
• The dendritic cells are most effective in presenting antigens to naive immunocompetent Th cells. They can carry a processed antigen from a site of inflammation to the T-cell rich areas of the lymph nodes

Question 11

What is the function of cytotoxic T-cells?

Answer 11

cytotoxic T cells mediate the direct, cellular killing of target cells, such as virally infected cells, tumors, or foreign grafts. Prevents infected cells from spreading to neighboring healthy cells (Tc cells)

Question 12

What is the function of Td cells?

Answer 12

They are involved in the inflammatory response and produce soluble mediators (lymphokines) that influence other cells, such as macrophages.

Question 13

What is the function of memory cells?

Answer 13

memory cells are also responsible for the accelerated response to a second antigenic challenge (the secondary immune response).

Question 14

What is the function of helper t-cells?

Answer 14

• These cells help with the antigen-driven maturation of B & T-cells and also enhances B & T-cell responses to antigens
• T cells inhibit both humoral and cell-mediated immune responses.
• Helper t cells bind to antigens, join with macrophages which secretes interleukin I.
• Tolerance involves recognition of self-antigens and active suppression of the immune system by suppressor t-cells

Question 15

How are B-cells activated?

Answer 15

1. When an immunocompetent b-cell encounters an antigen for the 1st time, and the antigen is complementary to its BCR (B-cell receptor), it is stimulated to proliferate and differentiate.
2. The differentiated B-cell becomes a plasma cell and can be found in the blood, spleen, or lymph nodes.
3. Each plasma cell acts as a factory producing antibodies specific for that antigen.

Question 16

Describe the primary immune response to an antigen

Answer 16

• During initial exposure to antigens, there is a latent period, or lag phase, during which b-cell differentiation and proliferation occur.
  
  • During the lag phase the necessary colonial selection, processing and presentation of antigens, induction of Th cells, and interactions between b-cells and Th-cells take place.
• Approx. After 5-7 days IgM antibodies specific for that antigen are produced.

Question 17

Describe the secondary immune response to an antigen

Answer 17

• It is a rapid production of a larger amount of the same antibodies that have been produced by the primary response.
• The response is more rapid due to memory cells that were produced by the primary response
• IgG production is increased considerably during this phasing, making it the predominant antibody class of this response.

Question 18

How are T-cells activated?

Answer 18

• T-cells are activated when an antigen binds to a specific receptor on the t-cell.
• The naive t-cell then proliferates and differentiates into a functional T-cell.
• The activated T-cells:
  
  1. Kill foreign / abnormal cells (carried out by T-cytotoxic cells)
  2. Assist/activate other cells, such as macrophages. (carried out by T-helper cells
  3. Produce T-memory cells.