Monocyte-derived recruiting activity: kinetics of production and effects of
endotoxin
E McCall and GC Bagby
Cultured monocytes release a factor, monocyte-derived recruiting activity
(MRA), which stimulates fibroblasts, endothelial cells, and T lymphocytes
to produce colony-stimulating activity (CSA). We studied the kinetics of
MRA production using a technique in which MRA levels were measured in a two
stage bioassay. We used umbilical vein endothelial cells as the
MRA-responsive (CSA-producing) cells, and normal colony-forming unit
granulocyte-macrophage (CFU-GM)-enriched bone marrow cells (T lymphocyte-
and monocyte-depleted, low density bone marrow cells) as the CSA-responsive
cells. MRA stimulated a 30- fold increase in CSA production by endothelial
cells. MRA production was detected in supernatants from as few as 10(3)
monocytes per milliliter, required the presence of fetal calf serum, and
was inhibited by cycloheximide (10 to 100 micrograms/mL) and puromycin (10
to 50 micrograms/mL). Production was detectable after 24 hours of monocyte
incubation, was maintained for three days, and fell to undetectable levels
by seven days. With the addition of bacterial endotoxin (lipopolysaccharide
[LPS]) (50 micrograms per 10(6) cells), MRA was detectable after only three
hours of incubation, and levels peaked at 24 hours. Further, maximum MRA
levels in the supernatants of LPS-stimulated monocytes were up to ten times
greater than peak levels in the supernatants of unstimulated monocytes.
Endotoxin augmented monocyte production of MRA to a greater extent than it
did CSA production, indicating that the stimulation of CSA production by
endotoxin may be at least partly indirect. The responsiveness of MRA
production to endotoxin in vitro is consistent with the notion that MRA may
be a biologically relevant regulator of CSA production by cells of the
hematopoietic microenvironment.
Volume 65,
Issue 3,
pp. 689-695,
03/01/1985
Copyright © 1985 by The American Society of Hematology
