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What is Malignant histiocytosis and explain in detail?
Malignant histiocytosis  is a rare hereditary disease found in the Bernese Mountain Dog and humans, characterized by histiocytic infiltration of the lungs and lymph nodes.  The liver, spleen, and central nervous system can also be affected.  Histiocytes are a component of the immune system that proliferate abnormally in this disease.  In addition to its importance in veterinary medicine, the condition is also important in human pathology.

Histiocytic disorders
A histiocyte is a differentiated tissue cell that has its origin in the bone marrow.  The source for histiocytes is the monocyte/macrophage line.  Monocytes (found in the blood) and macrophages (found in tissue) are responsible for phagocytosis (ingestion) of foreign material in the body.  Langerhans cells are dendritic cells found in the skin and function by internalizing antigens (foreign particles) and presenting them to T cells