Model of DC differentiation in the mouse spleen.

(1) Access of CD8α⁻ DCs to the marginal zone either from the blood via the marginal sinus (a) or by intrasplenic differentiation from an unknown precursor (b). (2) Transient retention of CD8α⁻ DCs in the marginal zone reticular meshwork. (3) Reversal of CD8α⁻ DC retention in the marginal zone. (4) Migration of CD8α⁻ DCs to the inner white pulp accompanied by the acquisition of the phenotypic and functional features of CD8α⁺ DCs. Finally, CD8α⁺ DCs die in situ or leave the spleen via lymph vessels (see “Discussion” for a detailed explanation). Principal changes accompanying the proposed maturation of CD8α⁻ DCs into CD8α⁺ DCs are indicated. IFN-γ indicates interferon γ.