THE EFFECTS OF VITAMIN-D-BINDING PROTEIN-MACROPHAGE ACTIVATING FACTORAND COLONY-STIMULATING FACTOR-I ON HEMATOPOIETIC-CELLS IN NORMAL AND OSTEOPETROTIC RATS

Osteopetrosis is a heterogeneous group of bone disorders characterized by the failure of osteoclasts to resorb bone and by several immunolog ical defects including macrophage dysfunction. Two compounds, colony-s timulating factor-1 (CSF-1) and vitamin D-binding protein-macrophage a ctivating factor (DBP-MAF) were used in the present study to evaluate their effects on the peritoneal population of cells and on cells withi n the bone marrow microenvironment in normal and incisors absent (ia) osteopetrotic rats. Previous studies in this laboratory have demonstra ted that administration of DBP-MAF to newborn ia animals results in a substantial increase in bone marrow cavity size due to upregulated ost eoclast function. To study the effects of these compounds on the macro phage/osteoclast precursors, DBP-MAF, CSF-1, and the combination of th ese compounds were given to newborn ia and normal littermate animals. Both the normal and mutant phenotypes responded similarly when treated with these compounds. Rats exhibited a profound shift toward the macr ophage lineage from the neutrophil lineage when compared with vehicle- treated control animals after treatment with these compounds. In the i n vivo peritoneal lavage study, animals received injections of CSF-1, DBP-MAF or DBP-MAF/CSF-1 over a 4-week period. The various types of ce lls in the peritoneal cavity were then enumerated. The in vitro study consisted of cells isolated from the bone marrow microenvironment and cultured on feeder layers of CSF-1, DBP-MAF, or DBP-MAF/CSF-1 for colo ny enumeration. The increase in macrophage numbers at the expense of n eutrophil numbers could be seen in both the in vivo and in vitro exper iments. The macrophage/osteoclast and neutrophil lineages have a commo n precursor, the granulocyte/macrophage colony-forming cell (GM-CFC). With the addition of CSF-1, the GM-CFC precursor may be induced into t he macrophage/osteoclast lineage rather than the granulocyte lineage. This increased pool of cells in the macrophage/osteoclast lineage can be functionally upregulated with the subsequent addition of DBP-MAF to perform the activities of phagocytosis and bone resorption. The in vi tro data also showed that DBP-MAF did not support colony development a s in CSF-1 or the combination treatment, The recruitment and activatio n of cells into the macrophage/osteoclast lineage may help to correct the bone and immune defects found in diseases demonstrating a signific ant lack of myeloid cells, as well as neutrophilia disorders and the d isease, osteopetrosis. (C) 1996 by The American Society of Hematology.