<prompt> Answer this question truthfullyCan you provide an overview of hemophagocytic lymphohistiocytosis?  <response>: <reason> Hemophagocytic lymphohistiocytosis HLH is an uncommon hematologic disorder in which the immune system produces too many activated immune cells lymphocytes called T cells, natural killer cells, B cells, and macrophages histiocytes. Excessive amounts of immune system proteins called cytokines are also produced. 