<prompt> Cell of origin of hairy cell leukemia is -B-cellT-cellNK-cellDendritic reticulum cell  <response>: Hairy cell leukaemia is an unusual uncommon form of B cell malignancy characterized by presence of hairy cells in the blood bone marrow splenomegaly.Hairy cells are abnormal mononuclear cells with hairy cytoplasmic projections which are seen in blood,bone marrow spleen.These cells exhibit CD19,CD20 CD22 antigen.Reference: Harsh mohan textbook of pathology 6 th edition pg no 379 