MATURATION OF PEYER PATCH DENDRITIC CELLS IN-VITRO UPON STIMULATION VIA CYTOKINES OR CD40 TRIGGERING

In mouse Peyer's patches (PP), dendritic cells (DC) are localized in T cell areas as NLDC145(+) CD11c(+) cells, and in the dome and corona r egion of the follicle as NLDC145(-) CD11c(+) cells, respectively, sugg esting the presence of two different DC populations with distinct role s in antigen uptake, processing, and presentation. However, it is not clear how this relates to DC maturation. In this report, we demonstrat e that freshly-isolated CD11c(+) DC have the properties of immature DC since they endocytose soluble antigens, phagocytose particulate mater ial such as latex beads, synthetize major histocompatibility complex ( MHC) class II and invariant chain, but, at the same time, display low stimulatory activity for resting T cells, as shown in mixed-lymphocyte reaction and oxidative mitogenesis assays. When cultured for 24 h in the presence of the cytokines granulocyte-macrophage colony-stimulatin g factor and tumor necrosis factor or anti-CD40, the cells undergo dra matic phenotypic and functional changes characteristic of DC maturatio n. After 24 h stimulation in vitro, CD11c(+) cells lose the ability to take up proteins such as ovalbumin, and in parallel with this decline , the biosynthesis of MHC class II and invariant chain is dramatically down-regulated or eliminated. On the other hand cells treated in vitr o exhibit on the cell surface higher levels of MHC class II, of co-sti mulatory molecules (CD80, CD86), of adhesion molecules (CD44, intercel lular adhesion molecule-1), and acquire expression of the interdigitat ing DC surface marker NLDC145. Concomitantly, the ability to stimulate naive T cells drastically increased after in vitro treatment with bot h stimuli. Taken together, our results indicate that the majority of D C in the PP are immature in terms of their antigen-uptake capacity. Th ese sentinel antigen presenting cells are strategically positioned at the dome region of PP, where antigens are transcytosed via the M cells from the gut lumen. A second population of mature interdigitating NLD C145(+) CD11c(+) DC stimulates naive unprimed T cells in interfollicul ar areas by up-regulation of surface ligands and accessory signals.