Interaction of silkworm larvae expressed monomeric hM-CSF with its receptor on murine bone marrow derived macrophage

Human macrophage colony-stimulating factor (hM-CSF) expressed in the silkworm larvae was monomeric. The nature of the interaction of iodinated monomeric M-CSF with murine bone marrow derived macrophage (BMM) was studied. On incubation with 2 nM [125I]M-CSF at 4 degrees C, approximately 90% of the maximal binding occurred within 15 min with a plateau around 1hr which then gradually declined. Scatchard plot analysis showed that the Kd for the monomeric M-CSF is 5.3 x 10(-10) M and the number of binding sites per cell is 4 x 10(4). Competition experiment indicated that cellular binding of the iodinated monomeric rhM-CSF was almost as effective as the native M-CSF. The results show that the interchain disulfide bond of M-CSF is not essential for the natural folding of active M-CSF.