Diferenciación y especialización funcional de las células dendríticas de ratón para la inducción de inmunidad innata y adaptativa

Abstract

Research developed in the last years has highlighted the functional specialization of the different subpopulations of dendritic cells (DCs) for the induction of inmune responses to different pathogens, although it remained to be solved some issues related to the identification of the DC subpopulations responsible for the induction of immunity against different virus, bacteria, fungi and parasites, as well as those implicated in anti-tumoral responses or allergy. In this sense, two important issues that remain to be addressed in depth are the cooperation between CD8+ DCs and pDCs in the induction of anti-viral CD8+ T cell responses, and the adquisition of the functional specialization by DCs responsible for the induction of Th2 responses. In the first part of this work we have analized the role of the pDCs in the adquisition of the functional specilization of CD8+ DCs. We have used FLt3L-DCs cultures, were we have found that three subpopulations of DCs, fenotipically very similar to those present in the mouse spleen (pDCs and, CD8+ and CD8- cDCs) can be generated. In contrast to previous published data, we found that the DC subset equivalent to the splenic CD8+ DCs (CD8+-lk DCs) were not able to complete the differentiation process, as evidenced by their defect in regulating CD8 and DEC-205 expression. However, they can cross-present antigens, similar to their in vivo counterparts, the CD8+ DC subset. After stimulation of Flt3L-DCs cultures with CpG, LPS or poly(I:C) we observed the regulation of CD8 and DEC-205 in the CD8+-lk DC subset, but only when stimulated in the presence of pDCs. In this sense, the production of IL-12 by cDCs generated in the Flt3L-DCs cultures in response to CpG or LPS also requires de presence of pDCs. In this regard, we have shown that the mechanism by which pDCs contribute to the regulation of CD8 expression in CD8+-lk DCs is dependent on type I IFN produced by pDCs. Finally, we propose that type I IFN could be responsible not only of the induction of the expression of CD8, but also could play a role in confering to the CD8+ DCs subpopulation the hability to cross-present antigens, to produce fast and efficiently IL-12 in response to microbial stimuli or the expression of the enzyme IDO, this last one responsible for their tolerogenic potential in steady state. In the second part of this work we have analized the effect of IL-4 produced during Th2 inmune responses on DCs derived from monocytes recruited to the infection site, or to the draining lympnodes. In this case we have used a different experimental approach based on the differentiation of DCs from purified monocytes with GM-CSF, in the presence or not of IL-4. The results obtained showed that IL-4 blocks the capacity of the DCs differentiated with GM-CSF+IL-4 to produce proinflamatory cytokines, such as IL-12, in response to LPS or CpG, but not in response to Zymosan. In the case of LPS stimulation, this blockade seems to de dependent of the expression and accumulation of a negative regulator that, based on the results we have obtained, could be SOCS1, which expression its strongly induced at mRNA level in the GM/IL-4 MoDCs. In conclusion, the DCs generated from monocytes recruited to an inflammatory area with a Th2 cytokine profile are not going to be able to produce IL-12 (cytokine essential in the induction of Th1 responses) after estimulation through a Th1 stimulus, derived from the same pathogen or expressed by a different pathogen.