T cell mediated immunity Overview Antigen presenting cells - - PowerPoint PPT Presentation

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Topics

• T cell mediated immunity

– Overview – Antigen presenting cells – Co-stimulation – Maturation of APC – Interleukine 2 (IL 2) – Clonal expansion

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Development in the thymus Naive T cells Blood Peripheral lymphoid tissue Ag (APC) Armed effector T cells

(Rapid action)

Target Cells

Primary cell- mediated immune response

Immunological memory

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Cell – Cell interactions in the Lymph Node

T cells enter lymph node T cells monitor APC If interaction, T cells proliferate and differentiate If no interaction, T cells leave Fig 8.2

Ag

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Pathogen products are transported to peripheral lymphoid tissues

• Peripheral sites to draining lymph nodes
• Blood to Spleen
• Mucosal surfaces to Peye’s Patches (MALT)
• T cells Enter via High endothelial venules
• Have contact with APC (Sample MHC)
• Receive survival signals
• If not activated they exit back into circulation

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Types of T cells

• Cytotoxic T

lymphocytes

– CD8+ – TCR recognizes

• MHC I
• endogenous peptide

– Killing of self cells

• infected with virus
• tumor cells
• Helper T lymphocytes

(T helper cells)

– CD4+ – TCR recognizes

• MHC II
• exogenous peptide

– Production of cytokines – Activation of macrophages – Immune response regulation

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Antigen Presenting cells

• Immature cells reside in the

tissues i.e Langerhans’ ( low MHC expression, high phagocytic activity)

• Upon activation by infection

they migrate to lymphoid

• rgans (high MHC

expression, no phagocytic activity) Dendritic Cells Macrophages

• Scavengers – innate immune

response

• Can present antigens in

MHC I and II and provide co-stimulation when activated B cells

• Bind to pathogens through surface

receptors

• Display peptides in MHC II
• Express co-stimulatory molecules in

response to stimuli by infection or cytokines

Fig 8.3

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Cell adhesion molecules stabilize cell- cell interactions SELECTINS Leukocyte homing

Fig 8.4

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Cell adhesion molecules stabilize cell-cell interactions INTEGRINS Leukocyte homing & Cell activation

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Adhesion molecules stabilize cell-cell interactions

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Priming Co-stimulation

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Co-stimulation

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Co-stimulation

Fig 8.12

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Improper Co-stimulation

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Activation only by professional APC

Fig 8.13

Activated Anergy

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Maturation of Dendritic cells

Fig 8.14

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B cell Ag presentation

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High affinity IL-2 receptor – Naïve T cells are small resting cells that have long lives – Infrequent divisions – Infrequent apoptosis – Upon activation, T cells enter cell cycle, divide and proliferate – Process mediated by IL-2

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Co-stimulation leads to IL-2 expression

Low affinity IL-2 receptor High affinity IL-2 receptor IL-2

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Clonal expansion

Fig 8.22

Naive T cells Activated T cells –No need for co-stimulation

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Cell-surface Molecule expression changes with activation of T cell