Med. Immunity L2 - Dendritic Cells

Dendritic cell

• Capture and present antigens to T-cells

• The only cells that can activate naive T-cells in vitro and in vivo

What kind of pathways do DC use when sampling/taking up mole.

Complementary endocytic pathways

Macropinocytosis

• Formation of large vesicles from the plasma membrane

• Constantly on immature dendritic cells

• uptakes a large amount of fluid with the antigen

• requires ruffles on DC surface

Dendritic receptors

C-type lectins : recognizes sugars

Fc receptos : antibodies

Scavenger : apoptopic bodies

Heat shock proteins : tumors or infected cells

Phagocytosis

• receptor mediated uptake of large particulate species

• receptor engagement activates phag.

Danger signals trigger dendritic cell maturation

1. Direct signals

   • toll-like receptors signalling bacteria etc

2. Indirect signals

   • molecule secretion from pathogens or responses to tissue damage

Migration of Dendritic cells

• in the perepheral tissue sampling fluid

• capture pathogens

• migrate to lymphoid tissues to present pathogens to t-cells

• travel through lymphatic vessels to where the t-cells are concentrated

Receptors for migration

1. Langerhan cells

2. CCR7 ligands

Antigen presentation by dendritic cells

• adaptive immune system

• only cells known that present to and activate naive t-cells

• t-cells recognize the antigens the chopped up antigen peptides

Do the receptors function in just receptor mediated endocytosis

No, also in phagocytosis

Immature DC

• Found in periphery (skin and mucosa)

• Efficient in capture but inefficient in presentation

Mature DC

• Inefficient in capture but Efficient in presentation

Examples of the complimentary endocytic pathways

Macropinocytosis - sample environment around it

Receptor mediated endocytosis - interact directly with pathogens

Phagocytosis - Capture entire pathogens

the MhC class 1 and 2 activate which t-cells

MHC 1- CD8

MH2 - CD4

what TLRs recognized by direct signals

TLR 2-5

2= Gram +

4-5 = Gram-

3= dsRNA

what is increased after TLR activation

Macropinocytosis

explain MHC 2 pathway

• ER processes MHC classes

• passed off to golgi

• antigen is endocytosized

• antigen peptides are bonded to the MHC

• MHC with peptide is brought to surface of the DC

explain MHC 1

• MHC1 is folded in the ER

• Antigens are processed int he ER

• Peptides are bonded to MHC

• go through golgi

• MHC 1 (heavy chain + B2) with peptide is presented to CD8 cells

What type of DC has high levels of MHC 1

mature

what is cross presentation

• unique to DC cells

• important for initiation of adaptive imm.

• present exogenous antigens on MHC class 1

what MHC is involved with cross presentation

MHC 1

What DC has low MHC 2

immature

What DC has high B7.1 and B7.2

Mature

what recptor on the the T cell is for B7

CD28

What are B7.1/2

stimulatory signals from the DC