Immunology Ch.10

CD28

critical for antigen activated T cells to synthesize the cytokine IL-2

CD40L

binds CD40 on APCs and B cells

costimulation

second signal that helps activate T cells and allows them to proliferate

Where do T cells mature

thymus

positive selection

ensures that immature thymocytes can recognize self-MHC molecules

What is positive selection essential for?

effective antigen recognition and immune function

What happens to cells unable to recognize self-MHC?

die by neglect

negative selection

eliminates developing T cells with high affinity for self-antigens

What does negative selection ensure?

the immune system doesn’t attack the body own tissues

What kind of cells are eliminated?

cells that bind self-peptide-MHC too strongly

What is negative selection a key step for?

central tolerance

Where do mature CD4 and CD8 T cells circulate?

through lymph nodes and other tissues

signal 1 of naive CD4 T cells

TCR + CD4 recognize peptide-MHC class II on an APC

signal 2 of naive CD4 T cells

costimulation, especially CD28-B7

APC-derived cytokines

influence helper T-cell differentiation

dendritic cells

important for activating naive T-cells

cytokines

short range communication molecules that direct immune responses

What secretes cytokines

activated T helper cells

major CD4 helper subsets

• Th1

• Th2

• Th17

• Treg

• Tfh

Th1

supports macrophage activation and responses to intracellular pathogens

Th2

supports responses to parasites and allergic inflammation

Th17

promotes inflammatory recruitment and defense against extracelluar microbes

Treg

help suppress excessive responses and maintain tolerance

Tfh

provides B-cell help, including CD40L-CD40 interactions

cytotoxic T lymphocytes (CTL)

recognize specific peptide-MHC I on an infected or abnormal target

How do CD8 CTLs kill target cells?

release specific enzymes that trigger apoptosis

What can trigger apoptosis?

• release of granenzymes

• Fas ligands on CTLs engaged on Fas on target cells

What can CD4 and CD8 both do?

• require antigen recognition and activation signals as naive T cells

• generate memory cells

memory T cells

respond more rapidly upon later exposure to the same antigen

NKT cells

respond to lipid antigens presented by CD1d

yD T cells

have a distinct TCR and contribute to early tissue defense