Jean E. Rinaldo

Role of alveolar macrophages in endotoxin-induced neutrophilic alveolitis in rats

Although bacterial endotoxins have potent effects on blood monocytes and tissue macrophages, the role of alveolar macrophages in regulating intrapulmonary neutrophil traffic following endotoxemia has not been studied previously. We have previously reported that a single intraperitoneal injection of endotoxin from Escherichia coli serotype 055B5 causes acute lung inflammation by neutrophils (PMN) in rats. The factors which influence the migration of PMN in the lung in this model are unknown. To determine whether macrophage-derived products could play a role in directing migration, we enumerated neutrophils in histologic sections and employed electron microscopy to document the location of neutrophils in the lung in vivo following endotoxin. We also cultured the alveolar macrophages recovered by lung lavage to measure the effect of their culture supernatants on neutrophil migration in vitro. In the first 6 hr following endotoxin, and also 24 hr later, there was an increase in the number of PMN enumerated in the lung parenchyma by light microscopy. Electron microscopy showed the location of the neutrophils to be exclusively intravascular at 6 hr. By contrast, neutrophils were observed in both interstitial and bronchoalveolar spaces at 24 hr, confirming that transvascular migration was active at that time. The pulmonary macrophages which were recovered by lung lavage from groups of rats sacrificed at 4 and at 15 hr following the administration of endotoxin were assayed for the release into culture media of migration-stimulatory activity for neutrophils. Macrophages from animals sacrificed 4 hr following endotoxin released less migration-stimulating activity into media than macrophages from controls. These macrophages could be stimulated to release migration-stimulating activity into culture media at levels comparable to macrophages from controls by the addition of opsonized Zymosan to the culture media. By contrast, macrophages from animals sacrificed 15 hr after endotoxin spontaneously released more migration-stimulating activity for neutrophils than did macrophages from controls. Thus, in this model, a specific increase in the synthesis or release by alveolar macrophages of factors which stimulate the migration of neutrophils in vitro coincided with a transition from intravascular to extravascular alveolar inflammation by neutrophils in vivo. These observations are consistent with the hypothesis that pulmonary alveolar macrophages may contribute to the regulation of alveolar inflammation following endotoxemia by releasing factors which influence the migration of neutrophils.

Shift in subfractions of rat alveolar macrophages in vivo during endotoxin-induced alveolitis.

To elucidate changes in alveolar macrophages that accompany sepsis‐induced lung injury, this study analyzed the subfractions of alveolar macrophages (AM) recovered by lung lavage during the onset of endotoxin‐induced acute neutrophilic alveolar inflammation in the rat model. Centrifugation on continuous self‐generated density gradients of Percoll was used to fractionate AM into subpopulations between density limits 1.012 and 1.130. Two‐thirds of AM recovered from pathogen‐free control rats (group C) were in a fraction with a density range of 1.058‐1.078 [“normal” density fraction, (ND)]. Only 6% were located in a very low density (VLD) fraction 1.037‐1.048. Neutrophils accounted for less than 1% of recovered cells and usually were found in the fraction with density range of 1.079‐1.130. By contrast, if rats underwent lung lavage 15 hours after the administration of endotoxin (group E), only 38% of macrophages were recovered in the “normal” density fraction, whereas 26% of the AM recovered were in the VLD fraction. This shift in the relative sizes of the density based subpopulations coincided with the onset of acute bronchoalveolar inflammation as indicated by the recovery of neutrophils by bronchoalveolar lavage (PMN = 7 × 104 in C, vs. 9.4 × 105 in E, p < .001). The macrophages on the low density subfractions showed functional impairment: they were less viable in culture and migrated poorly in response to endotoxin‐activated serum compared to macrophages in the “normal” density fraction from the endotoxin‐treated animals. The rapid emergence of the low density population after endotoxin could represent an influx of new cells, but more likely indicates that injury to or previous activation of resident macrophages has caused their density to decrease. We speculate that the emergence of a population of AM in airspaces with low density and impaired function could weaken pulmonary host defense following endotoxemia.

An Internist's View—Multiple Organ System Failure: The Intensivist as a Bewildered New Biologist

Practicing critical care medicine was never easy, even when we had the luxury of thinking about patients one organ at a time. Students and interns on rounds were trained to summarize problems “by systems.” The problems of the heart, lung, kidney, liver, and blood seemed discrete. Those days are nearly gone. In this issue of the Jotu-iirrl, Heard and Fink [I] have taken on the unenviable task of reviewing multiple organ failure syndrome (RIOFS), the ovemhelmingly complex unifj-ing diagnosis that many if not most critically ill patients are now presumed to hrive. So all-encompassing as to defy a satisfying definition, diagnostic criteria, or understanding of mechanism, hlOFS sometimes seems to be a syndrome defined by lumpers from hell. How did this happen to us, most of us having started out as gas exchange, lung water, and hemodynamically oriented pulmonologists? General surgeons, being practical people who for the most part lack a subspecialist’s organ-system bias, seemed to have recognized the obvious first. For intensivists trained in internal medicine, many of whom are pulmonogists, I believe the perception evolved slowly and painfully, largely in futile pursuit of a successful therapeutic approach to the adult respiratory distress syndrome (AIDS), a “pulmonary disease.” Initially, AKDS was perceived as a problem of too much water in the lungs and n’;ls approached confidently with diuretics, Swan-Ganz catheters, positive end-expiratory pressure, and the like. When the results were not edifying, it became fashionable to import from our colleagues in hematology a facile immunological explanation: blame the neutrophil[2]. Ofcourse, it turned out that the logical therapy for a neutrophil-mediated disorder, megadoses of corticosteroids, did not really work either [3]. hiore significantly, I’andora’s box was open: We had left the lung and crept into the netherworld of systemic phenomena and immunlogical cascades. Then when studies from Bell and colleagues [4] , hlontgomery and colleagues [5], and others appeared in the pulmonar). literature, scholarly pulmonologists discovered what surgeons and medical housestaff knew all along: Patients with “AIZDS” had a lot more wrong with them, often got infections, usually died if they seemed intractably “septic,” and did not die of respirator). failure. Now there is no turning back. We are stuck with a “multisystem” disorder of unfathomable complexity. I, and I suspect many others, feel vulnerable. I admit that I cannot really grasp this new disease MOFS (aka. Multiple-system organ failure [RISOF]). I think part of my confusion arises from the fact that there are several different overlapping phenomena going o n all at once. Here are some examples. Epidemiologically, a new category of patient with ovemvhelming immunodeficiency now crowds the intensive care units (ICUs) of university medical centers: patients with acquired immunodeficiency syndrome (AIDS), transplant patients, and recipients of aggressive combinations of chemotherapeutic agents. Their propensity to infection and multisystem failure may be an order of magnitude different from the patients with ARDS Ashbaugh and co-workers [b] described in 1967. They are sprinkled liberally throughout our clinical studies of ARDS-sepsisRIOSF syndromes, but they have not been clearly identified and tracked as a subset. There are other multisystem iatrogenic problems mixed in: Patients who develop nephrotoxicity From aminoglycosides, then suffer pulmonary edema from intractable volume overload, then septicemia from vascular access for dialysis will probably appear in some clinical study as more patients with “multiple-system failure.” Finally, the lumpers not withstanding, all organs are not alike. When for whatever reason certain ones fail utterly, like the liver in a patient awaiting transplant [7] or the gastrointestinal barrier in a surgical patient with chronic anastomotic breakdown, a multisystem disa t e r is inevitable. Iiuman survival requires that the liver remove waste, toxins, and sundry bioactive mediators, and that the gastrointestinal niucosa stand behveen us and our fecal effluvium. Abnormalities of these diverse phenomena often arc