Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Hemophagocytic lymphohistiocytosis ?
    ### Response:
    Hemophagocytic lymphohistiocytosis (HLH) is a condition in which the body makes too many activated immune cells (macrophages and lymphocytes). People with HLH usually develop symptoms within the first months or years of life which may include fever, enlarged liver or spleen, cytopenia (lower-than-normal number of blood cells), and neurological abnormalities.
    