Pathogenetic mechanisms of the hemophagocytic syndrome (HPS).

The HPS is precipitated by an immune stimulus, most often Epstein-Barr virus (EBV), in the context of defective cytolytic function. T cells and NK cells are stimulated to produce a variety of cytokines, including interferon-γ. These stimulate accessory cells, which in turn produce chemokines leading to further stimulation and activation of macrophages and T and NK cells. In the setting of a defective cytolytic response, the cycle of stimulation continues uninterrupted.