Topic 4: Adaptive Immunity

Question 1

What are the three types of T lymphocytes

Answer 1

• helper cells
• regulatory cells
• cytotoxic cells

Question 2

What is adaptive immunity?

Answer 2

immune response mediated by B and T lymphocytes to infectious agents and noninfectious molecules

Question 3

What are the differences between innate and adaptive immunity

Answer 3

Innate
- detects common microbial structures
- receptors are encoded in the germline
- same response upon repeat exposure
- immediate response
Adaptive
- detects vast repertoire of molecules -> can be very specific
- receptors generated by somatic recombination
- improved adapted response to repeat exposure
- delayed response

Question 4

What are antigens

Answer 4

• a foreign molecule from a pathogen

Question 5

What types of antigens are recognized by B cells

Answer 5

• proteins
• lipopolysaccharides
• lipids
• nucleic acids

Question 6

What types of antigens are recognized by T cells

Answer 6

• peptides derived from proteins

Question 7

How do T and B cells differ in how they associate with antigens

Answer 7

• T cells require antigen presentation be dedicated antigen presenting cells
• B cells directly recognize its cognate antigen

Question 8

What are the two forms of adaptive immunity

Answer 8

• humoral immunity and cellular immunity

Question 9

What is humoral immunity

Answer 9

-directed against extracellular microbes
- mediated by B lymphocytes
- B lymphocytes secrete antibodies that neutralize and eliminate microbes and microbial toxins

Question 10

What is cellular immunity

Answer 10

• directed against intracellular microbes
• mediated by T lymphocytes
• T lymphocytes activate phagocytes and lymphocytes or kill infected host cells

Question 11

What is the function of Humoral Immunity

Answer 11

use B lymphocytes to block infection and eliminate extracellular microbes

Question 12

What is the function of cell-mediated immunity by helper t cells

Answer 12

activate macrophages to kill phagocytosed microbes

Question 13

What is the function of cell-mediated immunity by cytolytic t cells

Answer 13

kill infected cells and eliminate reservoirs of infection

Question 14

What are the phases of the immune response?

Answer 14

• Recognition
• Activation
• Effector Phase
• Decline
• Memory

Question 15

What is the Recognition phase

Answer 15

naive lymphocytes recognize corresponding antigens

Question 16

What is the Activation phase

Answer 16

lymphocytes differentiate and start clonal expansion

Question 17

What does activation require?

Answer 17

activation requires two signals, antigen receptor binds antigen (signal 1). Microbial or innate immune signals are also required for lymphocyte activation; can be cytokines, chemokines

Question 18

What is clonal expansion

Answer 18

• when a BCR or TCR dectects an antigen the B cell or T cell undergoes multiple rounds of cell division, thereby expanding. Each daughter is identical to the parent cell

Question 19

What is the effector phase?

Answer 19

differentiated lymphocytes initiate microbial elimination

Question 20

What is the decline phase

Answer 20

after microbial elimination the signal for lymphocyte activation disappears. Most of the cells activated by antigen die by a process of programmed cell death (apoptosis)

Question 21

What is the memory phase

Answer 21

remaining cells become memory lymphocytes, which can result in stronger responses to subsequent challenges with the same antigen

Question 22

What are B lymphocytes

Answer 22

• each BCR recognizes a distinct microbial 3-dimensional structure
• naive B cells are activated by antigens and another second signal
• activation leads to proliferation and diffferentation into effector cells that secrete antibodies. BCR productions is now modified that BCR is secreted as an antibody

Question 23

What is an antibody

Answer 23

• released into circulation and mucosal fluids by B cells upon infection
• neutralizes microbes and microbial toxins
• stops microbes from gaining access to host cells
• does not have access to intracellular microbes

Question 24

What are antigen presenting cells

Answer 24

T lymphocytes require antigen presentation from antigen presenting cells (APC). APCs capture, process and present antigens to T lymphocytes in lymphoid tissues

Question 25

What are the two types of T lymphocytes

Answer 25

• CD4 helper T cells
• CD8 cytolytic T cells

Question 26

What are CD4+ helper T cells

Answer 26

• detect antigens presented by professional antigen presenting cells.
• secrete cytokines to activate other components of the immune response (macrophages)
• have class II MHC that help in presentation of antigen to helper T cells

Question 27

What are CD8+ cytolytic T cells

Answer 27

detect microbial antigens presented by all nucleated cells and destroy the presenting cells
- have class I MHC that present cystolic antigen to cytolytic T lymphocytes

Question 28

What is the peripheral lymphoid organs

Answer 28

• lymph nodes
• spleen
• mucosal and cutaneous lymphoid tissues
• concentrate antigens and lymphocytes to optimize interactions

Question 29

What is the lymphatic system

Answer 29

• a network that transports fluids from tissues through lymph nodes and ultimately to the circulatory system (initially to veins)
• excess interstitial fluid is collected by the lymphatic system and is processed by lymph nodes prior to being deposited into the circulatory system
• lymphatic system is not closed and has no central pump

Question 30

How are T lymphocytes activated in the lymph nodes

Answer 30

• APCs drain from peripheral tissues into lymph nodes
• T lymphocytes enter lymph nodes
• APCs activate T lymphocytes
• Lymphocytes exit lymph nodes and enter circulation, then exit circulation into inflamed tissue where they mediate microbial destruction