Dendritic cells have tentacles but are otherwise unrelated

Follicular Dendritic Cells are associated with daughter B cells in Germinal Centers

Not of bone marrow origin (but mesenchyme)

Nonphagocytic; do not present antigen to T cells (but to B)

Express

–          Fcγ receptor

–          Complement receptors CR1, CR2, CR3

Trap antigens complexed with IgG, C3b, or C3d

In lymphoid follicles (LN, spleen, MALT)

At Germinal centers, present trapped antigen to daughter B cells  to select for high-affinity Fab

Timer starts; B cells must bind the antigen presented by FDC or die

BCRs that bind with high affinity get a survival signal

–          Memory B cells with high affinity BCR

–          Plasma cells that produce strong-binding antibodies

(???) APCs responsible for long-term retention of antigens in some peripheral lymphoid organs

___________________________________________________________________________________

Interdigitating Dendritic Cells are associated with CD4+ T cells at LN paracortex

Class II MHC molecules

Hematopoietic stem cell origin

Immature: Langerhans cells at skin and mucosa

–          Phagocytic but not co-stimulatory

–          Endocytose invading protein antigen

–          As ‘veiled cell’, migrate afferent lymphatic vessel to T cells in LN paracortex

–          Stimulate induction of either TH1 or TH2 subset from naïve CD4+ T cells

Career: Professional APC; nonphagocytic

Constituatively express B7, class II MHC molecules

Thymocyte selection

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