Stimulatory Lipids Accumulate in the Mouse Liver within 30 min of Contact Sensitization to Facilitate the Activation of Naive iNKT Cells in a CD1d-Dependent Fashion

Natural killer T cells with invariant alpha beta-T cell receptors (TCRs) (iNKT cells) constitute a lipid-responsive arm of the innate immune system that has been implicated in the regulation or promotion of various immune, infectious and neoplastic processes. Contact sensitivity (CS), also known as contact hypersensitivity or allergic contact dermatitis, is one such immune process that begins with topical sensitization to an allergen and culminates in a localized cutaneous inflammatory response after challenge with the same allergen. CS depends on events initiated early in sensitization by hepatic iNKT cells. We have shown previously that these iNKT cells release IL-4 early after skin sensitization to activate B-1 B cells to produce IgM antibodies that aid in local recruitment of the effector T cells. Here, we utilize adoptive transfer techniques in several strains of knockout mice to demonstrate that hepatic lipids isolated 30 min after sensitization are significantly more stimulatory to naive hepatic iNKT cells than hepatic lipids isolated after sham sensitization. These stimulatory hepatic lipids specifically affect iNKT cells and not B-1 B cells. The downstream CS response is abrogated with anti-CD1d-blocking antibodies, suggesting a critical role of CD1d in the activation of hepatic iNKT cells with these lipids. Hepatocytes may not be essential, as donor hepatic iNKT cells can reconstitute CS without migrating to the recipient mouse liver. Rather, CD1d-expressing liver mononuclear cells are sufficient for activation of iNKT cells. In conclusion, stimulatory lipids accumulate in the liver soon after sensitization and facilitate iNKT cell activation in a CD1d-dependent yet potentially hepatocyte-independent manner.