Presence of the factor increasing monocytopoiesis (FIM) in rabbit peripheral blood during an acute inflammation.

An intraperitoneal injection of latex in rabbits was found to give rise to an increase in the number of macrophages at the site of inflammation and a concomitant monocytosis in the peripheral blood. The results showed that during the initial phase of the inflammatory reaction a humoral factor is present in the circulation of these animals that stimulates the monocyte production in the bone marrow in a concentration-dependent way. This factor has been called the factor increasing monocytopoiesis (FIM), in analogy with the name given to the factor previously found in mice. Rabbit FIM is cell-line specific since it has no effect on granulocyte or lymphocyte production, has an estimated molecular weight of between 10,000 and 25,000 daltons, was found to be sensitive to treatment with proteases, to be unaffected by glycosidases, and to be readily inactivated in vitro at 37 degrees C. Neither rabbit nor mouse FIM is species specific, since rabbit FIM evoked moderate monocytosis in mice and vice versa.