title: Enhancement of the biologic effects of interleukin-3 in vivo by anti-interleukin-3 antibodies.
abstract: Interleukin-3 (IL-3) has been shown to be a promising agent in the stimulation of bone marrow regeneration following myeloablative therapy. The biologic half-life of this agent is very short (5 to 15 minutes), which limits the effectiveness of low-dose therapy. Here we show that the biologic effects of low-dose IL-3 in mice may be enhanced by concurrent use of polyclonal anti-IL-3 antibodies. The biologic effects of IL-3 in vivo were enhanced dramatically by the combination of the cytokine and polyclonal rabbit anti-IL-3 antibodies, which recognized a peptide comprising the first 29 amino acids of the IL-3 molecule. Enhancing effects were not apparent in vitro, where weak neutralizing properties were observed for these antibodies. The mechanism of this enhancement by the antibody appears to be via a ninefold reduction in the total-body clearance of the cytokine in vivo. The apparent volumes of distribution for IL-3 and for the IL-3/antibody complex were surprisingly similar and exceeded the expected intravascular volume. The prolonged biologic half-life of IL-3 was reproducibly associated with a threefold to fivefold increase in splenic mast-cell precursors over levels observed in mice treated with IL-3 alone; increases in the numbers of mature mucosal-type mast cells in the spleen, but not in the jejunum or lung; increases in IL-3-dependent colony-forming unit-cell in the spleen; and an apparent redistribution of mast cells away from the bone marrow. These experiments demonstrate that antibodies to a cytokine can enhance the biologic activity of that cytokine in vivo.
authors.affiliation: Biomedical Research Centre, University of British Columbia, Vancouver, Canada.
authors.forename: A T
authors.initials: AT
authors.lastname: Jones
authors.forename: H J
authors.initials: HJ
authors.lastname: Ziltener
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology*; D000936:Antigen-Antibody Complex; D002850:Chromatography, Gel; D003114:Colony-Forming Units Assay; D006207:Half-Life; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D007377:Interleukin-3 / Q000737:chemistry / Q000276:immunology / Q000493:pharmacokinetics / Q000494:pharmacology*; D008407:Mast Cells / Q000166:cytology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008811:Mice, Inbred DBA; D008970:Molecular Weight; D011817:Rabbits; D013154:Spleen / Q000166:cytology
chemical_list: D000906:Antibodies; D000936:Antigen-Antibody Complex; D007377:Interleukin-3