Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Castleman disease ?
    ### Response:
    What causes Castleman disease? The exact underlying cause of Castleman disease (CD) is poorly understood. However, some scientists suspect that an increased production of interleukin-6 (IL-6) by the immune system may contribute to the development of CD. IL-6 is a substance normally produced by cells within the lymph nodes that helps coordinate the immune response to infection.
    