BIO 343 Lecture Notes - Lecture 8: Interleukin 2, Cell Membrane, Epithelium

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27 May 2018

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Immunology Chapter 8: T-Cell Mediated Immunity

Hayden Casassa

• T cell Activation (or priming)

o Atiatio of atue aïe T ells  atige peseted to the  APC’s

o Leads to proliferation and differentiation into effector T cells

o This first phase of a primary adaptive immune response occurs in secondary lymphoid tissue

• Properties/Functions of Effector T cells

o Effector T cells are terminally differentiated activated T cells

▪ Examples are CD4, TH1, TH2, TFH, TH17, and CD8 cells

• Antigens present in tissues must be taken to secondary lymphoid tissues

o Antigens in skin and other peripheral tissues go to draining lymph node

o Antigens in blood primarily go to spleen

o Antigens in Respiratory tract go to BALT (or tonsils)

o Antigens in GI System go to GALT (or peyers patches or appendix)

• Antigen capture and initiation of primary immune responses are carried out mainly by Dendritic cells

o Myeloid Dendritic cells: process and present antigen in context of MHC Class 1 or 2

o Dediti Cells ae ette tha APC’s uz the a igate fo ifetio to lphoid tissues

• Macrophages are present in 2nd lymphoid tissue and engulf pathogens entering via afferent lymph

o Play a critical role in preventing pathogens from entering blood

• Immature Myeloid dendritic cells process the antigen

o These cells migrate to T cell area of 2nd lymphoid tissue and differentiate into mature dendritic

cells which present antigen to naïve t cells

o These dendritic cells in the skin are known as Langerhans cells

• Immature dendritic cells are not in lymphoid tissue and have ability to capture and process antigen

o Dendritic cells migrate to lymphoid tissue to mature and MHC I/II expression increases as they

mature

o When matured, they are in secondary lymphoid tissue and can activate T cells and are located

in t cell area of lymph nodes

• Macropinocytosis

o Nospeifi uptake of hatee is aoud hih ould otai ateia, fluid, athig

• Viral (nonlethal) infection

o Dendritic cells can be infected and if not lethal,

• Transfer of Viral Antigen

o If virus is lethal, infected dendritic can migrate to secondary lymphoid tissue and transfer

antigen to healthy dendritic cell who presents it to CD8 T cells

o This is known as cross-presentation

o Cross-priming the immune system. Important if the virus only infects non-APC’s ut euies

CD8 T cells to be activated in 2nd Lymph tissue to eliminate the infection

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TCR

MHC

CD28

• B Cells use BCR to uptake extracellular antigen for processing and presentation via MHC Class 2 to CD4

T cells

o Main antigens they process are small soluble antigens such as toxins.

o B cells are not phagocytic

• Macrophages use phagocytosis and micropinocytosis to uptake extracellular antigens for processing via

Class 2 MHC to CD4 T cells

• Naïve T cells first encounter antigen presented by dendritic cells in secondary lymphoid tissue

o Naïve Mature T cell arrives from blood→ crosses the HEV in the node→ T cell area →mingles

ith dediti ells….

▪ If deditis ae’t pesetig Ag, T ells eit ia effeet

▪ If naïve mature T cells specific for Ag (in blue) are specific for Ag on APC, then they

clonally expand and are activated into effector T cells

• Naïve T cells can enter the lymph nodes from the blood or from afferent lymph coming from an

upstream lymph node

o Circulating Naïve t cells can live for many years in search of antigen

• Activation of naïve T cells require signals from the TCR and a Co-stimulatory Receptor

o Naïve T cells that leave thymus require two major signals to be activated

▪ 1: Binding to MHC/peptide via TCR and CD4/CD8

T cell

APC

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Document Summary

If virus is lethal, infected dendritic can migrate to secondary lymphoid tissue and transfer antigen to healthy dendritic cell who presents it to cd8 t cells: this is known as cross-presentation, cross-priming the immune system. Important if the virus only infects non-apc"s (cid:271)ut (cid:396)e(cid:395)ui(cid:396)es. Cd8 t cells to be activated in 2nd lymph tissue to eliminate the infection: b cells use bcr to uptake extracellular antigen for processing and presentation via mhc class 2 to cd4. T cells: main antigens they process are small soluble antigens such as toxins, b cells are not phagocytic, macrophages use phagocytosis and micropinocytosis to uptake extracellular antigens for processing via. If de(cid:374)d(cid:396)iti(cid:272)s a(cid:396)e(cid:374)"t p(cid:396)ese(cid:374)ti(cid:374)g ag, t (cid:272)ells e(cid:454)it (cid:448)ia effe(cid:396)e(cid:374)t. They need both in order to be activated and signal. Binds il-2 with low/moderate affinity: once activated, t cells express high affinity il-2 receptor and secrete il-2 cytokine, high affinity il-2r consists of a,b,y, chains, secreted il-2 can bind on same cell (autocrine)

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