Partial characterization of a low-molecular-weight, macrophage-derived inhibitor of DNA synthesis: a possible immunoregulatory molecule.
It has been previously reported that tumor-associated macrophages isolated after combination therapy contained an activity that inhibited thymocyte proliferation in the IL-1 comitogenic assay. The present report shows that this macrophage-derived inhibitory factor (MDIF) inhibits DNA synthesis in diverse adherent and nonadherent cells in vitro. The elution pattern seen after chromatography using Bio-Gel P10 or Sephadex G-25 columns indicated a molecular size of 3-6.5 kDa. However, full activity was retained when MDIF was passed through an Amicon filtration membrane having a cut off of 500 Da. It was also seen that other molecules less than 500 Da, such as thymidine, thimerosal, and PGE2, each of which was also shown to be growth inhibitory, eluted in a size range similar to that of MDIF after chromatographic separation. Ion exchange chromatography confirmed that MDIF was distinct from thymidine, and a radioimmunoassay indicated that PGE2 was not responsible for MDIF activity. Little or no inhibitory activity could be detected in macrophages isolated from progressing tumors or from tumors excised after cyclophosphamide treatment of tumor bearers. Given that this inhibitory activity was associated with macrophages derived from tumors induced to regress by combination therapy, the possibility is discussed that MDIF may play an important role during the regulation of immune reactions at the tumor site.
Evans
R
R
Jackson Laboratory, Bar Harbor, Maine 04609.
Duffy
T M
TM
Coleman
D L
DL
Tai
H H
HH
D000276:Adjuvants, Immunologic / Q000302:isolation & purification / Q000494:pharmacology*; D000818:Animals; D003520:Cyclophosphamide / Q000378:metabolism / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis*; D015232:Dinoprostone / Q000032:analysis / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D008264:Macrophages / Q000032:analysis*; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D008970:Molecular Weight; D009374:Neoplasms, Experimental / Q000276:immunology; D013849:Thimerosal / Q000032:analysis; D013936:Thymidine / Q000032:analysis / Q000378:metabolism
D000276:Adjuvants, Immunologic; D013849:Thimerosal; D003520:Cyclophosphamide; D004247:DNA; D015232:Dinoprostone; D013936:Thymidine