 1. to better characterize the mechanisms underlying such disease and the possible response to the treatment. In particular: i we will investigate the immunophenotypic and histomorphologic features of ECD histiocytes; ii we will gather gene expression data from peripheral blood immune cells to better characterize their functional status, to define their transcriptional fingerprints and their possible modulation as a result of tocilizumab treatment; iii we will assess the production of soluble mediators and the expression of activation molecules by monocytes derived from ECD patients, as well as after stimulation with selected inflammatory cytokines; iv we will investigate the ex vivo and in vitro impact of tocilizumab treatment on those markers, for possible use as a predictor or indicator of response to treatment. 