Mast cells and histamine metabolism in skin lesions from MRL/MP-lpr/lpr mice

It is likely that mast cell and histamine metabolism are involved in autoimmune tissue injury such as cutaneous lupus erythematosus (LE) because different histamine receptors can regulate Th1 and Th2 cells. In order to verify the role of the axis of mast cell–histamine metabolism–histamine receptor, the autoimmune mouse has been investigated. The MRL/Mp-lpr/lpr (MRL/lpr) mouse is a good model for the spontaneous development of skin lesions similar to those seen in human LE. In skin lesions from MRL/l mice, there are many infiltrating T cells and mast cells in the dermis and impaired histamine metabolism, in which the low activity of histamine-N-methyltransferase and the related prolonged effects of histamine in the skin tissue seem to play a definite pathological role in the development of spontaneous lupus-like eruptions. The expression of H2R on the mast cell decreases within these skin lesions at 5 months of age. It is interesting that the activity of HMT runs in parallel with the expression of H2R over the time course of the skin changes in MRL/l mice, but the relationship between these two observations remains obscure. The accumulation of mast cells expressing H2R and prolonged effects of histamine may occur to regulate the production of Th1 and Th2 cytokines in the skin lesions of MRL/l mice.