Distribution of histamine among leukocytes and platelets.

M OST OF THE HISTAMINE of human blood is found iii the buffy coat.2 ‘ Earlier attempts to identify the histamine-carrying constituent of this leukocyte-platelet layer have been unsuccessful.4 Because human platelets, lymphocytes in lymph nodes, amid momiocytes from exudates have all been found to contain little histamimie, amid because blood histamine remains normal imi pathological conditions in which these elememit.s are abnormally abundant., histamimie has been assigned, by exclusion, to the gramiulocytes. It has seemed unlikely that neutrophils are rich iii histamine because in leukocytosis blood histamine is miot greater than normal.5 Code stated imi 1937 that “the eosinophil is in most cases a source in blood of the histamine-like activity,” while in 1952 he wrote that “the histamine comitent of the blood may r may not be increased when eosinophils are present.. Ceitainly eosimiophils often do not contain histamine. Sometimes they may.” The comicept of eosimiophils as facultat.ive histamine carriers is also foumid in the somew’hat later publication of Code and Mitchell.6 Because of the high blood level of histamine iii chromiic myelocytic leukemia, immature forms of granulocytes would be thought to comitaili large amoumlts of histamimle if it were not for the low blood histamimie accompanying even greater abumidance of these forms imi acute leukemia, for instance. Until very iecently,m ‘