Ultrastructural and cytochemical evaluation of sepsis‐induced changes in the rat pulmonary intravascular mononuclear phagocytes

Abstract

Sepsis stimulates an increase in the number and activity of mononuclear phagocytes in systemic host-defence organs. The present study was conducted to define the ultrastructural and cytochemical characteristics of the mononuclear phagocytes that sequester in the lung microvasculature of septic rats. Fourteen rats were challenged with a single intraperitoneal injection of saline (0n5 ml\100 g), E. coli (2i10(\100 g) or glucan (4 mg\100 g), and euthanased 2, 4, or 7 d later. The lungs were inflation fixed and processed for transmission electron microscopy. Cellular morphology was used to identify the intravascular mononuclear phagocytes and acid phosphatase (AcPase) expression was monitored as an index of cellular differentiation and activation. Control rats contained a limited number of monocytes in the pulmonary vasculature. In contrast, large numbers of activated mononuclear phagocytes were seen in the microvasculature within 48 h of treatment with either microbial product. The recruited pulmonary intravascular mononuclear phagocytes (PIMP) exhibited AcPase-reactive Golgi complexes, accumulation of secretory vesicles and other features of cell activation consistent with enhanced biosynthetic activity. Subsequent electron microscopy, conducted 4 and 7 d posttreatment, suggested that a progressive decline in the number and activity of PIMPs then occurred. In order to quantify the sepsis-induced accumulation of AcPase-positive PIMP, the experimental challenges were repeated in 11 rats and, 48 h later, tissue samples were evaluated by light microscopy for tartrate-insensitive acid phosphatase. Control rats exhibited 0n148p0n107 AcPase-positive PIMP\alveoli. E. coli and glucan challenged animals exhibited significant (P 0n01) increases in AcPase-positive mononuclear phagocytes, with 0n782p0n073 and 0n636p0n170 PIMP\alveoli respectively. The results demonstrate that focal sepsis stimulates a significant, but transient, recruitment of activated mononuclear phagocytes into the rat pulmonary microvasculature.

Pulmonary intravascular monocytes/macrophages in a rat model of sepsis

“…Although it is accepted that monocytes/macrophages enter alveoli following a multistep paradigm that includes vascular margination and effacements, very little attention has been paid to the recruitment and functions of intravascular monocytes/macrophages in lung inflammation. Previously we have reported ultrastructural evidence that a single challenge with E. coli induces recruitment of PIMMs by 48 hr, followed by their disappearance at 96 hr (Singh et al, 1998). Now we have used light and electron microscopic immunocytochemistry to show that recruited PIMMs in the rat react with ED-1 antibody.…”

“…We have previously shown that recruited PIMMs represent a transient population and their numbers peak at 48 hr in our model (Singh et al, 1998). To determine their contributions to lung inflammation, we challenged rats with E. coli LPS at 48 hr post-E. coli infection and compared lung inflamma- Fig.…”

“…Roles of neutrophils and monocytes/macrophages recruited into the alveoli in sepsis-induced lung injury have been addressed by various studies (Cox et al, 1995;Ishii et al, 1998;Ellaban et al, 2004;Lomas-Neira et al, 2006). However, there is morphologic evidence for recruitment of pulmonary intravascular monocytes/macrophages (PIMMs) in a rat model of E. coli-induced sepsis (Singh et al, 1998). Also, there is some evidence that marginated monocytes in the vasculature of endotoxemic mouse lung modulate the lung inflammation through TNF-a-dependent upregulation of adhesion molecules on the endothelium (O'Dea et al, 2005).…”

Pulmonary intravascular macrophages: prime suspects as cellular mediators of porcine CARPA

“…In species where PIMs are not found at birth, their appearance in the lung can be induced by different effects, for example stimulation with lipopolysaccharides (LPS) or infectious agents, or by changes in the general condition of the organism, such as the presence of hepatic cirrhosis, tumors, hematologic diseases or experimental ligation of the bile duct (12,13). Pulmonary induction of PIM cells in the lung was described in rats, mice, hamsters, rabbits, chicken, dogs and macaques (14)(15)(16).…”

Pulmonary intravascular macrophages and lung health: What are we missing?

“…The globular surface coat of PIMs, probably anchored via a glycosyl-phosphatidyl inositol anchor, complexes with blood-borne materials such as tracer particles and endotoxins and mediates their endocytosis (3,43,46). PIM colonization of the lung occurs either early after birth in some species (constitutive PIMs) (28,65), later upon stimulation with lipopolysaccharide (LPS) and bacteria, or in conditions such as cirrhosis (induced PIMs) (11,13,45). Of the animals tested, the orders Artiodactyla (pigs, sheep, goats, llamas, reindeer, water buffalo) and Perissodactyla (horse; Fig.…”