Developmental regulation of granulocytic cell binding to hemonectin. Hemonectin (HN), a component of the bone marrow (BM) extracellular matrix which promotes adhesion of cells in the granulocytic lineage, was purified to near homogeneity and tested for its ability to mediate attachment of normal and leukemic cells of granulocytic lineage. Purified HN immobilized on plastic substrates promoted serum-free attachment of normal granulocyte/macrophage progenitor cells (CFC-GM), using an in situ attachment assay in which cell attachment is inhibited by specific polyclonal antisera. When unfractionated BM cells were allowed to attach to purified HN and stained in situ, HN preferentially bound cells at earlier stages of granulocytic differentiation. These observations were confirmed using cells of the HL-60 progranulocytic cell line which mirrored this differentiation-stage specific binding to HN. HN promoted attachment of 60% of uninduced HL-60 cells which were arrested at the progranulocyte stage, whereas only 15% of uninduced HL-60 cells attached to uncoated plastic and 4% to attached plastic coated with equal microgram quantities of bovine serum albumin (BSA). When HL-60 cells were induced to differentiate along the granulocytic pathway by incubation with dimethylsulfoxide (DMSO), attachment to hemonectin was reduced. Thus, both primary BM granulocytic cells and a granulocytic cell line show preferential attachment of those cells at earlier stages of differentiation. This developmentally regulated binding suggests a mechanism for release of maturing BM into the peripheral circulation. 