There are differences in immune responses according to gender. Women have stronger responses against pathogens, especially viruses but are also more susceptible to develop autoimmune diseases. These points reflect more robust innate and adaptive responses in women. Plasmacytoid dendritic cells (pDCs) are key actor of innate immune responses through their ability to produce large amounts of type 1 Interferons (IFN1) secondary to stimulation of their toll like receptors (TLR) 7 and 9 by nucleic acids. Thus, pDCs play a major beneficial role in antiviral responses. In autoimmune diseases like Systemic Erythematous Lupus, pDCs also play a role, mostly deleterious, through inappropriate production of IFN1 upon stimulation of their TLR's by self nucleic acids. In these diseases, pDCs from women have been demonstrated to produce more IFN1 as compared to men, a phenomenon that can be linked to both hormonal and genetic factors. Indeed, the investigators research team demonstrated that IFN1 production by human pDCs can be increased by oestradiol through a specific receptor present in pDCs. Regarding genetics, some studies recently shown in a humanized mouse model, that pDCs developing from female hematopoietic precursor cells have an enhanced TLR 7 mediated IFN1 response as compared to male ones. These results indicate that X chromosome dosage could contribute independently to the enhanced TLR 7 mediated response of pDCs from women. Although some genes implicated in IFN1 production are on the X chromosome, including TLR 7, the mechanism underlying this observation are presently unknown.