Phagocytosis of apoptotic or necrotic cells differentially regulates the transcriptional expression of IL-12 family members in dendritic cells

Uptake of apoptotic cells by DCs is considered to contribute to induction and maintenance of immunological tolerance. TolDCs are sought after as cellular therapy in transplantation and autoimmunity and can be generated in vitro using GCs. In this study, we investigated how uptake of dead cells affects the production and expression of different members of the IL-12 family by immature DCs or TolDCs. We show that compared to regular immature DCs, TolDCs display elevated levels of PS-recognizing bridge molecule receptors αvβ5 and CD36, and have enhanced phagocytic abilities with accelerated uptake of apoptotic cells. We confirm that apoptotic cell uptake results in diminished production of IL-12p40 and IL-12p70 by DCs. We now show that this also results in increased expression of IL-12p35 and Ebi3. TolDCs completely lack expression of IL-12p40 yet have enhanced levels of Ebi3 and IL-12p35. Uptake by TolDCs of apoptotic or necrotic cells does not affect the expression of Ebi3/IL-12p35 and also does not increase IL-12p40. This is distinct from the culture of immature DCs with necrotic cells, which is sufficient to induce IL-12p40 secretion. Conversely, ingestion of apoptotic cells by DCs leads to increased expression of IL-12p35 and Ebi3 without affecting IL-12p40. In conclusion, we have shown that uptake of apoptotic versus necrotic cells by DCs differentially regulates members of the IL-12 family. Apoptotic cells favor expression of Ebi3 and IL-12p35, and we propose that differential regulation of the IL-12 family is an additional mechanism in determining the immune response to dying cells.