Immunology Chapter 8 – T-cell mediated immunity
The dendritic cell – innate immune system
• In periphery DC are immature
o Phagocytosis (by CLR uptake)
o No activation of naïve T cells
• DC mature through TLR stimulation
• In lymph nodes DC are mature
o Low phagocytic capacity
o Activate naïve T cell
DC are in tissues (lungs, gut, skin and lymphoid organs) where they take up
pathogens by their dendrites and present them to naïve T cells
2 points where T-cells recognize antigen
1. Activation naïve T cell by DC
a. Extracellular: CD4+ T cell recognize MHC class II
b. Intracellular: CD8+ T cell recognize MHC class I
2. Recognition by effector T-cell
a. Extracellular: helper T-cell
b. Intracellular: cytotoxic T-cell
Activation of naïve T cells by DC
3 signals:
1. Antigen presentation in the context of MHC – activation (signal 1)
Immature DC take up antigen in tissue --> move via the afferent
lymphatic vessel to the lymph node (in lymph nodes DC are
mature) --> they settle in the T-cell areas to found their T-cell
Naïve T cells move via the blood through HEV or via afferent
lymph vessels (not already in round 1!) to the lymph node
Round 1: Naïve T cells enter lymph node via HEV:
• MHC-peptide complex recognition; retention in lymph node for
activation
• No MHC-peptide complex recognition; T cells leave lymph via efferent
lymph vessel and continue search
Round 2: Following unsuccessful round 1 naïve T cells can:
• Enter an upstream lymph node via afferent lymphatics
• Return to the blood circulation and enter a new lymph node via HEV
MHC class II:
• Receptor-mediated endocytosis of bacteria
• Micropinocytosis of bacteria or viruses
MHC class I:
• Viral infection
• Cross-presenting of exogenous viral antigens
The dendritic cell – innate immune system
• In periphery DC are immature
o Phagocytosis (by CLR uptake)
o No activation of naïve T cells
• DC mature through TLR stimulation
• In lymph nodes DC are mature
o Low phagocytic capacity
o Activate naïve T cell
DC are in tissues (lungs, gut, skin and lymphoid organs) where they take up
pathogens by their dendrites and present them to naïve T cells
2 points where T-cells recognize antigen
1. Activation naïve T cell by DC
a. Extracellular: CD4+ T cell recognize MHC class II
b. Intracellular: CD8+ T cell recognize MHC class I
2. Recognition by effector T-cell
a. Extracellular: helper T-cell
b. Intracellular: cytotoxic T-cell
Activation of naïve T cells by DC
3 signals:
1. Antigen presentation in the context of MHC – activation (signal 1)
Immature DC take up antigen in tissue --> move via the afferent
lymphatic vessel to the lymph node (in lymph nodes DC are
mature) --> they settle in the T-cell areas to found their T-cell
Naïve T cells move via the blood through HEV or via afferent
lymph vessels (not already in round 1!) to the lymph node
Round 1: Naïve T cells enter lymph node via HEV:
• MHC-peptide complex recognition; retention in lymph node for
activation
• No MHC-peptide complex recognition; T cells leave lymph via efferent
lymph vessel and continue search
Round 2: Following unsuccessful round 1 naïve T cells can:
• Enter an upstream lymph node via afferent lymphatics
• Return to the blood circulation and enter a new lymph node via HEV
MHC class II:
• Receptor-mediated endocytosis of bacteria
• Micropinocytosis of bacteria or viruses
MHC class I:
• Viral infection
• Cross-presenting of exogenous viral antigens
