Macrophages and translymphatic absorption represent the first line of host defense of the peritoneal cavity
D. L. Dunn, R. A. Barke, D. C. Ewald and R. L. Simmons
To quantitate the host defenses of the rat peritoneal cavity, nonviable
radiolabeled Escherichia coli were injected intraperitoneally and
clearance, leukocyte influx, and phagocytosis were examined. Macrophages
(MCs) were present initially and remained relatively constant in number.
The polymorphonuclear leukocyte (PMN) response began at one to two hours
and was maximal at 24 to 72 hours. A previously unidentified
inoculum-dependent PMN response was defined. Clearance and phagocytosis
were extremely rapid, and few (less than 3%) free bacteria were present
after two hours. Phagocytic activity of MCs and PMNs was identical, but MCs
were numerically predominant initially and thus accounted for the majority
of early phagocytosis. Thus, MC phagocytosis and clearance represent the
primary line of host peritoneal defenses. We hypothesize that the
subsequent inoculum-dependent PMN response may have evolved to cope with
those larger inocula for which this initial response is inadequate.
