Quantitation of specific myeloid cells in rat bone marrow measured by in vitro 35S-sulphate incorporation

A biochemical measurement which can be used for quantitation of specific early myeloid cells in rat bone marrow has been developed. This measurement consists of a rapid, simple assay for the in vitro quantitation of ³⁵S-sulphate incorporation into rat bone marrow cells. Incubation of bone marrow cells with ³⁵S-sulphate led to a time-dependent increase in radioactivity obtained in perchloric acid insoluble fractions of bone marrow cell suspensions. This incorporation was inhibited by cyanide and puromycin. Autoradiography has demonstrated the radiolabel to be specifically associated with immature cells of the myeloid series. The cells most active in this respect were eosinophils. When rats were treated with endotoxin, the rate of ³⁵S-sulphate incorporation was increased. Cell number measurements, using conventional histopathology and a Coulter Counter, demonstrated that endotoxin caused an initial release of mature granulocytes from the bone marrow. The regeneration of this mature population in the marrow was rapid, and was characterized by an increase in the number of immature cells and a concomitant increase in the rate of ³⁵S-sulphate incorporation measured in preparations of bone marrow cells in vitro. Furthermore, this response to endotoxin has demonstrated that Coulter Counting techniques can be used to distinguish specific populations of cells (e.g. mature granulocytes) within the bone marrow.