Topic 3: Linking innate and adaptive immunity

Question 1

Where to antigens in tissue go?

Answer 1

• The lymph nodes

Question 2

Where to antigens in blood go?

Answer 2

• The spleen

Question 3

What happens to a dendritic cell when it encounters a pathogen, how does it become activated?

Answer 3

• The dendritic cell use various membrane receptors to bind to microbe/its antigen
• The dendritic cell will engulf the pathogen or its antigen via phagocytosis whilst at the same time products of the microbe (PAMPs) are stimulating PRRs such as TLRs within the dendritic cell
• The dendritic cell will begin to secrete cytokines such as IL-1 and TNF; these in combination with the TLR signalling cause the dendritic cells to active
• Activation of dendritic cells involves their loss of adhesiveness for epithelia and they begin to express the chemokine receptor CCR7

Question 4

How do activated dendritic cells migrate from tissue to the draining lymph nodes?

Answer 4

• The dendritic cell is activated by cytokines and TLR signalling during antigen capture
• The dendritic cell starts to express CCR7 receptor on its surface
• CCR7 is a chemokine produced by lymphatic endothelium and by stromal cells in the T cell zones of lymph nodes
• The dendritic cell will exit the epithelium and migrate through the lymphatic vessels following the CCR7 chemokine gradient
• During this migration the dendritic cell matures into an APC expressing the antigen in the groove of MHC II
• Naive T cells also express CCR7 receptors so they are also attracted to the same T-cell zones where they can interact with dendritic cells

Question 5

What is the basic time course of an adaptive immune response?

Answer 5

Day 0: antigen presenting cell presents antigen to naive T lymphocyte; Naive B lymphocyte bind to antigen in fluid
Days 1-6: clonal expansion of specific B and T cells with correct receptors
Day 7: differentiation of specific B and T cell clones into effector cells (plasma cells and effector T cells)
Day 7-14: elimination of antigen via humoral and cell-mediated immunity
Day 14-20: contraction of response, apoptosis of cloned cells
Long term: memory T and B cells with receptors for the antigen survive

Question 6

What are the important properties of the adaptive immune response?

Answer 6

• specificity: highly specific
• diversity: can respond to a diverse range of antigens
• memory: leads to rapid and enhanced responses to repeated exposures to the same antigen
• clonal expansion: increases number of antigen specific lymphocytes
• specialisation: generates responses that are optimal for defence against different types of microbes
• contraction and homeostasis
• non-reactivity to self