Presence of pulmonary intravascular macrophages in the equine lung: some structuro-functional properties

A critical assessment of the cellular defences of the avian respiratory system: are birds in general and poultry in particular relatively more susceptible to pulmonary infections/afflictions?

In commercial poultry farming, respiratory diseases cause high morbidities and mortalities, begetting colossal economic losses. Without empirical evidence, early observations led to the supposition that birds in general, and poultry in particular, have weak innate and adaptive pulmonary defences and are therefore highly susceptible to injury by pathogens. Recent findings have, however, shown that birds possess notably efficient pulmonary defences that include: (i) a structurally complex three-tiered airway arrangement with aerodynamically intricate air-flow dynamics that provide efficient filtration of inhaled air; (ii) a specialised airway mucosal lining that comprises air-filtering (ciliated) cells and various resident phagocytic cells such as surface and tissue macrophages, dendritic cells and lymphocytes; (iii) an exceptionally efficient mucociliary escalator system that efficiently removes trapped foreign agents; (iv) phagocytotic atrial and infundibular epithelial cells; (v) phagocytically competent surface macrophages that destroy pathogens and injurious particulates; (vi) pulmonary intravascular macrophages that protect the lung from the vascular side; and (vii) proficiently phagocytic pulmonary extravasated erythrocytes. Additionally, the avian respiratory system rapidly translocates phagocytic cells onto the respiratory surface, ostensibly from the subepithelial space and the circulatory system: the mobilised cells complement the surface macrophages in destroying foreign agents. Further studies are needed to determine whether the posited weak defence of the avian respiratory system is a global avian feature or is exclusive to poultry. This review argues that any inadequacies of pulmonary defences in poultry may have derived from exacting genetic manipulation(s) for traits such as rapid weight gain from efficient conversion of food into meat and eggs and the harsh environmental conditions and severe husbandry operations in modern poultry farming. To reduce pulmonary diseases and their severity, greater effort must be directed at establishment of optimal poultry housing conditions and use of more humane husbandry practices.

Lung Inflammation Associated With Clinical Acute Necrotizing Pancreatitis in Dogs

Although dogs with acute necrotizing pancreatitis (ANP) can develop respiratory complications, there are no data describing lung injury in clinical cases of ANP in dogs. Therefore, we conducted a study to characterize lung injury and determine if pulmonary intravascular macrophages (PIMs) are induced in dogs with ANP ( n = 21) compared with control dogs ( n = 6). Two pathologists independently graded histologic sections of pancreas from clinical cases to characterize the severity of ANP (total scores of 3–10) compared with controls showing histologically normal pancreas (total scores of 0). Based on histological grading, lungs from dogs with ANP showed inflammation (median score, 1.5; range, 0–3), but the scores did not differ statistically from the control lungs (median score, 0.5; range, 0–2). A grid intersects-counting method showed an increase in the numbers of MAC387-positive alveolar septal mononuclear phagocyte profiles in lungs of dogs with ANP (ratio median, 0.0243; range, 0.0093–0.0734, with 2 outliers at 0.1523 and 0.1978) compared with controls (ratio median, 0.0019; range, 0.0017–0.0031; P < .0001). Only dogs with ANP showed labeling for von Willebrand factor in alveolar septal capillary endothelial cells, septal inflammatory cells, and alveolar macrophages. Toll-like receptor 4 and interleukin 6 were variably expressed in alveolar macrophages and septal inflammatory cells in lungs from both ANP and control dogs. Inducible nitric oxide synthase was detected in alveolar macrophages of dogs with ANP only. These data show that dogs with ANP have lung inflammation, including the recruitment of PIMs and expression of inflammatory mediators.

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

Pulmonary intravascular macrophages (PIMs) are constitutively found in species such as cattle, horse, pig, sheep, goat, cats, and whales and can be induced in species such as rats, which normally lack them. It is believed that human lung lacks PIMs, but there are previous suggestions of their induction in patients suffering from liver dysfunction. Recent data show induction of PIMs in bile-duct ligated rats and humans suffering from hepato-pulmonary syndrome. Because constitutive and induced PIMs are pro-inflammatory in response to endotoxins and bacteria, there is a need to study their biology in inflammatory lung diseases such as sepsis, asthma, chronic obstructive pulmonary diseases, or hepato-pulmonary syndrome. We provide a review of PIM biology to make an argument for increased emphasis and better focus on the study of human PIMs to better understand their potential role in the pathophysiology and mechanisms of pulmonary diseases.

Tissue and Cell Tropism of African Horse Sickness Virus Demonstrated by Immunoperoxidase Labeling in Natural and Experimental Infection in Horses in South Africa

Tissues from 196 experimental and confirmed natural cases of African horse sickness (all 9 serotypes) were examined with a standardized and validated immunohistochemical assay for detection of the causative virus. The study confirmed that heart and lung are the main target tissues for African horse sickness virus (across all serotypes), followed closely by spleen. It also indicated that microvascular endothelial cells and monocyte–macrophages are the main target cells for virus replication. The importance of monocytes as target cells was emphasized, with relatively few tissue macrophages containing antigen in the lung and spleen, respectively. The results were largely in agreement with those of previous studies, but the large number of cases examined permitted more precise description of the location and distribution of antigen in different tissues. Comparison with descriptions of tissue and cell tropism of other orbiviruses indicated similarity with African horse sickness. Immunohistochemistry was shown to be a useful and consistent technique for demonstrating target cells, but the difficulty of identifying cell types—in particular, different types of monocyte–macrophages—is a limitation.

Thin and strong! The bioengineering dilemma in the structural and functional design of the blood-gas barrier

In gas exchangers, the tissue barrier, the partition that separates the respiratory media (water/air and hemolymph/blood), is exceptional for its remarkable thinness, striking strength, and vast surface area. These properties formed to meet conflicting roles: thinness was essential for efficient flux of oxygen by passive diffusion, and strength was crucial for maintaining structural integrity. What we have designated as "three-ply" or "laminated tripartite" architecture of the barrier appeared very early in the evolution of the vertebrate gas exchanger. The design is conspicuous in the water-blood barrier of the fish gills through the lungs of air-breathing vertebrates, where the plan first appeared in lungfishes (Dipnoi) some 400 million years ago. The similarity of the structural design of the barrier in respiratory organs of animals that remarkably differ phylogenetically, behaviorally, and ecologically shows that the construction has been highly conserved both vertically and horizontally, i.e., along and across the evolutionary continuum. It is conceivable that the blueprint may have been the only practical construction that could simultaneously grant satisfactory strength and promote gas exchange. In view of the very narrow allometric range of the thickness of the blood-gas barrier in the lungs of different-sized vertebrate groups, the measurement has seemingly been optimized. There is convincing, though indirect, evidence that the extracellular matrix and particularly the type IV collagen in the lamina densa of the basement membrane is the main stress-bearing component of the blood-gas barrier. Under extreme conditions of operation and in some disease states, the barrier fails with serious consequences. The lamina densa which in many parts of the blood-gas barrier is <50 nm thin is a lifeline in the true sense of the word.

In vivo interaction of pulmonary intravascular macrophages with activated platelets in microvessels of equine lung after multiple exposures to halothane, isoflurane, and thiamylal: A comparative ultrastructural and cytochemical study

The pulmonary intravascular macrophages (PIMs) of equines contain a unique electron-dense surface coat that is predominantly composed of lipoproteins. A single exposure of inhalatory halothane causes mobilization of the surface coat into the endocytotic system of the PIMs, followed by expansion of the Golgi apparatus and its enrichment with acid phosphatase. Simultaneously, the cells of the lymphocytic series show hyperplasia in the form of mitotic changes inside the microvascular compartment of the lung. Halothane is known to cause acute and chronic hepatotoxicity because of its biotransformation into trifluoroacytelated polypeptides. The present study was designed to examine the comparative effects of reexposures of inhalatory doses of halothane, isoflurane, and the intravenous barbiturate thiamylal sodium in ponies to evoke a stronger response in the PIMs after four exposures at increasing intervals of 1, 2, and 6 weeks. Ultrastructural and cytochemical evidence is presented that halothane induced translocation of the surface coat into the vacuolar system of the PIMs, followed by expansion of the Golgi apparatus and its enrichment with acid phosphatase. The cell membrane was thrown into extraordinary lamellipodial extensions, which enabled the PIMs to interact with platelets within the narrow confines of the pulmonary capillaries. The relationship between PIMs and platelets developed into large platelet aggregates. Isoflurane and thiamylal sodium did not affect the circulating platelets, although the surface coat was translocated into the endolysosomes in both situations. Although isoflurane is a lipid-soluble inhalant anesthetic similar to halothane, it is subject to very little biotransformation after use and in the present model demonstrates no immune response.

Some recent advances on the study and understanding of the functional design of the avian lung: morphological and morphometric perspectives

The small highly aerobic avian species have morphometrically superior lungs while the large flightless ones have less well-refined lungs. Two parabronchial systems, i.e. the paleopulmo and neopulmo, occur in the lungs of relatively advanced birds. Although their evolution and development are not clear, understanding their presence is physiologically important particularly since the air- and blood flow patterns in them are different. Geometrically, the bulk air flow in the parabronchial lumen, i.e. in the longitudinal direction, and the flow of deoxygenated blood from the periphery, i.e. in a centripetal direction, are perpendicularly arranged to produce a cross-current relationship. Functionally, the blood capillaries in the avian lung constitute a multicapillary serial arterialization system. The amount of oxygen and carbon dioxide exchanged arises from many modest transactions that occur where air- and blood capillaries interface along the parabronchial lengths, an additive process that greatly enhances the respiratory efficiency. In some species of birds, an epithelial tumescence occurs at the terminal part of the extrapulmonary primary bronchi (EPPB). The swelling narrows the EPPB, conceivably allowing the shunting of inspired air across the openings of the medioventral secondary bronchi, i.e. inspiratory aerodynamic valving. The defence stratagems in the avian lung differ from those of mammals: fewer surface (free) macrophages (SMs) occur, the epithelial cells that line the atria and infundibula are phagocytic, a large population of subepithelial macrophages is present and pulmonary intravascular macrophages exist. This complex defence inventory may explain the paucity of SMs in the avian lung.

In situ heparin-induced peroxisomal reticulum and biogenesis of peroxisomes in pulmonary intravascular macrophages (PIMs) of caprine lung: an ultrastructural and cytochemical study

Pulmonary intravascular macrophages (PIMs) contain a unique electron-dense globular surface-coat which is sensitive to heparin treatment, halothane anesthesia, and the digestive effect of lipolytic lipase (LPL), suggesting that the coat is predominantly composed of lipoproteins. In the present study, evidence is presented that heparin, when administered intravenously in goats, potentiated both the translocation of the surface-coat into the vacuolar system and the expansion of the Golgi apparatus. Sequentially, these changes were followed by proliferation of peroxisomes in combination with peroxisomal reticulum (PR), a transient precursor of this organelle. The peroxisomes, as well as PR, reacted positively for catalase after aldehyde fixation and 3,3'-diaminobenzidine (DAB) staining. In addition to their role as phagocytes, the ultrastructural and cytochemical detection of peroxisomes suggests a functional capacity of the PIMs, which may be adaptable to the circulating level of free fatty acids (FAAs).

Ultrastructural response of pulmonary intravascular macrophages to exogenous oestrogen in the bovine lung: translocation of the surface-coat and enhanced cell membrane plasticity and angiogenesis

The pulmonary intravascular macrophages (PIMs) of domestic ungulates are recognised by their specific surface coat, consisting of linearly arranged globules along the external leaf of the plasma membrane. The coat is sensitive to in vitro digestion with lipolytic lipase (LPL), intravenous heparin and clinical exposure to halothane anaesthesia. The sensitivity to these experimental manipulations suggests that the globules of the coat are predominantly composed of lipoproteins (LDL). The present administration of oestradiol proprionate in castrated male calves potentiated the translocation of the surface coat into the endocytotic pathway of the PIMs. Concurrently with mobilisation of the coat, the plasma membrane was thrown into prominent arrays of lamellipodial extensions. The sprawling macrophages made extensive adhesive contacts with the lining endothelium of the capillaries. Consequently, the endothelial cells were highly attenuated and precariously maintained the integrity of the vascular wall. At some focal points, the vascular wall was penetrated by the filopodial processes of PIMs, which protruded into the perivascular space. Furthermore, there were signs of neovascularisation in the form of overt mitotic changes, sprouting and precursor capillary formation. It is conceivable that the evolving profile of angiogenesis is due to the vascular endothelial growth factor (VEGF) paracrine function of PIMs. Endothelial cell specificity has been considered an important advantage of VEGF for neovascularisation. It allows pleotrophic response of endothelial cells to proliferate and to assemble into endothelial tubes.

Estrogen-induced microvilli and microvillar channels and entrapment of surfactant-lipids by alveolar type I cells of bovine lung

The ATI cells are simple, flat squamous epithelial cells, which are evolved to function as a component of the alveolar-capillary membrane, ideally designed for gaseous exchange. They inherently lack an active metabolic machinery and lead a precarious existence in the face of hostile environment. On the other hand, the ATI cells of the lung of ruminating animals are endowed with structure-functional properties which enable them to exert a selective barrier function against a wide range of osmotic pressure gradients at their luminal surface. Such gradients are created by a complex gaseous homeostasis due to expectoration of several gases and volatile fatty acids originating from the complex stomach of the ruminants. The purpose of this study is to examine the effect of estradiol propionate on the ultrastructure of the ATI cells and their interaction with the surfactant lipids. The lungs of estrogen and dexamethasone treated male calves were harvested for electromicroscopic examination. The evidence is presented that estradiol induced the formation of microvilli and microvillar channels at the luminal surface. At these regional modifications, intense interactions with the surfactant lipids and their entrapment into the pathways of endocytosis, took place in the squamous part of the ATI cells. Concurrently, large basal protrusions ended up as long lamellipods deep into the alveolar interstitium. The filamentous cytoskeletal network and microtubules intermixed with the translocated organelles such as Golgi apparatus and associated coated and uncoated vesicles. The results of this study support the hypothesis that estrogen regulate the selective barrier-function of the ATI cells. The entrapment of surfactant lipids under the influence of estrogen by ATI cells is a significant change perhaps in response to extracellular stimuli and expression of transmembrane receptors. It implies that these epithelial cells are specially evolved to adapt to a complex gaseous homeostasis in the lung of the ruminating ungulates.

Quantifying rat pulmonary intravascular mononuclear phagocytes

Cells of the mononuclear phagocyte system (MPS) protect the host by clearing effete and foreign particulates from the circulation. The current study was designed to identify, quantify, harvest, and provide a partial functional characterization of the systemic host-defense cell located in the pulmonary microvasculature of the rat. Critical colloid doses of test particulates (monastral blue B [MBB] or polystyrene beads) were infused intra-arterially into anesthetized rats so that phagocytically active pulmonary intravascular phagocytes could be identified. Morphologic characterization of in situ phagocytes was performed using electron microscopy. The number of active phagocytes was then determined using tissue samples processed for light microscopy. Finally, sequential perfusion of the pulmonary vasculature with buffer, chelating agent, and collagenase allowed elution and preliminary functional characterization of the pulmonary intravascular mononuclear phagocyte (PIMP). Electron microscopy demonstrated that both mononuclear phagocytes and neutrophils contributed to pulmonary sequestration of circulating particulates. Light microscopy showed that the microvasculature of each alveolus contained 0.50+/-0.19 active mononuclear phagocytes and 0.14+/-0.12 active neutrophils. A chelation/collagenase elution technique was then used to harvest the PIMP. Histologic evaluation of the postperfusion lungs indicated that 80% of the active phagocytes were removed by the technique. In total, the elution fluids contained 2.63+/-1.04 x 10(7) cells, with 1.60+/-0.78 x 10(7), 0.49+/-0.17 x 10(7), and 0.54+/-0.26 x 10(7) of those cells being mononuclear phagocytes, neutrophils, and lymphocytes, respectively. Functionally, the mononuclear phagocyte population exhibited a spectrum of phagocytic activities, with 51.5+/-19.5% of the cells being inactive, 33.9+/-13.4% exhibiting moderate phagocytic activity, and 14.6+/-9.8% demonstrating intensive phagocytic capacity. The current study provides the first quantified demonstration that mononuclear phagocytes are primarily responsible for sequestering blood-borne foreign particulates in the pulmonary circulation of the rat. Approximately 2 x 10(7) PIMP existed in the lungs of 300 gram rats. The functionally heterogeneous mononuclear phagocytes exhibited phagocytic capacities ranging from avidly phagocytic (14.6+/-9.8%) through moderately active (33.9+/-13.4%) to inactive. The lung microvasculature's large pool of inactive mononuclear phagocytes may provide a recruitable mechanism to allow significant increases in clearance of circulating particulates. A resident pool of activatable mononuclear phagocytes might explain previous clinical observations of increased particulate localization in the lung microvasculature of septic patients.

Acute pulmonary lesions in sheep experimentally infected with bovine viral diarrhoea virus

Six sheep, aged 6-8 months and seronegative for pestivirus, were inoculated intranasally, through the tracheal wall, and intrabronchially with a non-cytopathogenic isolate of bovine viral diarrhoea virus (ncpBVDV). Infected sheep were killed in pairs on post-inoculation day (PID) 2, 4 and 6. They all exhibited transient leucopenia or lymphopenia, or both. Platelet counts decreased but remained within normal limits. BVDV was isolated from buffy coats and tissues of all sheep inoculated with ncpBVDV but not from two uninfected control animals. Pulmonary lesions, evident in ncpBVDV-inoculated sheep, consisted of moderate oedema with multifocal alveolar septal necrosis and haemorrhage, infiltrates of mononuclear inflammatory cells, and degenerative changes in alveolar epithelium, endothelium and pulmonary intravascular macrophages. Additionally, there was morphological evidence of platelet activation and pulmonary intravascular macrophage stimulation. Lesions were not observed in the two control sheep.

Structural responses of pulmonary intravascular macrophages in lentivirus-infected and/or recombinant ovine interferon-tau-treated lambs

Ovine lentivirus (OvLV), a retrovirus, infects and disseminates to various tissue organs via monocytes. The differentiation of infected monocytes into macrophages is a prerequisite for viral replication, and the presence of infected macrophages in tissue organs induces chronic immunopathology such as lymphoid interstitial pneumonia. The pulmonary intravascular macrophage (PIM) is a recently identified mononuclear phagocyte in domestic animal species, including sheep. Recombinant ovine interferon-tau (roIFN-tau), a type I IFN originally named as the ovine trophoblast protein, has potent antiviral activity against OvLV and human immunodeficiency virus and prevents the development of OvLV-associated lung pathology. We investigated and compared the structural features of PIMs in OvLV-infected and/or roIFN-tau-treated 1-month-old lambs using transmission electron microscopy. The PIMs' numerical counts were performed in toluidine blue-stained sections of Epoxy-embedded lung tissues. A reduction in the number of PIMs was observed with OvLV infection and/or roIFN-tau treatment of lambs as compared to the control group (P < or = 0.05). The majority of the PIMs in OvLV-infected and/or roIFN-tau-treated groups were devoid of their surface coat. The PIMs of OvLV-infected lambs exhibited signs of biosynthetic activation such as expanded rough endoplasmic reticulum, prominent Golgi complexes, and accumulation of secretory vesicles. A few PIMs contained OvLV-like structures. In roIFN-tau-treated OvLV-infected lambs, the lymphocytes had ruffled plasma membranes and were in intimate contact with the PIMs, as is observed during cytotoxic cell-mediated killing of target cells. Most of the PIMs in roIFN-tau-treated OvLV-infected lambs appeared smaller in size. Ovine lentivirus and roIFN-tau, individually or in combination, alter the integrity of the surface coat of PIMs and cause their disappearance from the lungs. Ovine lentivirus infection induces morphological changes that correlate with cytotoxic cell behavior between lymphocytes and PIMs in roIFN-tau-treated or placebo-treated lambs. The loss of PIMs, probably infected with OvLV, either through direct killing by roIFN-tau or indirectly by roIFN-tau-activated cytotoxic T lymphocytes may represent different aspects of therapeutic actions of this cytokine.

Ultrastructural and immunocytochemical study of the pulmonary intravascular macrophages of Escherichia coli lipopolysaccharide-treated sheep

BACKGROUND

Pulmonary intravascular macrophages (PIMs) of sheep, cattle, goats, and horses have a novel heparin-sensitive chain of globules, called a surface coat, on their plasma membrane. The globules are arranged at a distance of 32-39 nm from the plasma membrane of PIMs. Intravascular nonbiological tracer particles complex with these globules prior to their endocytosis by the PIMs.

METHODS

We conducted a preliminary in vivo time-course study in sheep to investigate responses of the coat globules to a single dose of Escherichia coli lipopolysaccharide (E. coli LPS). Six sheep (6-9 months of age) were used in this study, and five of them were intravenously injected with E. coli (1 microgram/kg body weight) and euthanised at 3, 8, 10, 30, and 180 min (n = 1 each) after treatment. One sheep injected with saline solution served as the control. Acid phosphatase (AcPase) cytochemistry and immunocytochemistry using a polyclonal antibody were employed to localize secretory activity and E. coli LPS respectively in the PIMs.

RESULTS

The surface coat of PIMs disappeared rapidly following the LPS administration. Escherichia coli LPS micelles and coat globules were colocalized as a complex in the endosomes of PIMs. At 8-10 min following the treatment, endosomal and the other membranes were disrupted, and the LPS was identified in cytoplasm and nuclear matrix of PIMs simultaneously with the development of pulmonary interstitial edema. Progression of AcPase reactivity along the nucleus-Golgi complex axis coupled with intense buildup of coated transport vesicles within 30 min of the LPS injection suggested enhanced biosynthetic activity in the PIMs.

CONCLUSIONS

This study provides initial data on the sensitivity of the coat globules and their possible role in the endocytosis of E. coli LPS by the PIMs. Rapid biosynthetic activation of PIMs concurrent with loss of the coat and treatment with the LPS probably results in the secretion of inflammatory substances and contributes to the enhanced susceptibility of sheep to endotoxin-induced lung pathology.

Surface coat of sheep pulmonary intravascular macrophages: reconstitution, and implication of a glycosyl-phosphatidylinositol anchor

BACKGROUND

Pulmonary intravascular macrophages (PIMs) of sheep have a globular surface coat that facilitates endocytosis of tracer particles and Escherichia coli lipopolysaccharide, and is disrupted by the heparin and Brefeldin A treatments. The present study investigated the in vivo dynamics of the coat globules following heparin-mediated removal, and the mechanism of globule organization on the plasma membrane of PIMs in vitro.

METHODS

Sheep were administered heparin at a dose of 50 IU/kg body weight IV, and euthanised at 30 min, 3, 6, 12, 48, and 120 hr (n = 2 for each treatment) after the treatment. Control sheep (n = 2) were injected with normal saline solution. The tissues were processed for an ultrastructural examination and acid phosphatase (ACPase) cytochemistry. Heparin-treated lungs were subjected to morphometric analysis of the coat globules. Lung tissues from normal sheep (n = 2) were incubated with phosphatidylinositol-specific-phospholipase C (PIPLC; 2 IU/ml PBS) in vitro for 30 and 75 min.

RESULTS

Heparin study: The ultrastructural and morphometric data showed that the coat globules were removed at 30 min and reconstituted within 48 hr of the treatment. The PIMs showed prominent Golgi complexes associated with secretory vesicles, microtubules, and centriole between 3-12 hr of heparin treatment. Acid phosphatase cytochemistry also demonstrated secretory activity in the Golgi complexes of PIMs during the coat reconstitution. PIPLC study: The coat globules of PIMs were removed in a time-dependent mode by the PIPLC treatment without damage to other cell organelles.

CONCLUSIONS

This study demonstrates a time-dependent reconstitution of the coat of PIMs in conjunction with secretory activity following heparin-mediated removal, probably through sequestration of the globules from blood. This ability is of functional significance as the coat mediates particle endocytosis by the PIMs. The results also suggest the presence of a glycosyl-phosphatidylinositol (GPI) anchor in tethering of globules on the plasma membrane of PIMs to offer a structural basis for their integrity in pulmonary vascular flow.

Technetium 99m sulfur colloid scintigraphy to evaluate reticuloendothelial system function in dogs with portasystemic shunts

In a retrospective study, technetium 99m sulfur colloid scintigraphy was used to evaluate reticuloendothelial system function in 61 dogs with single congenital and 40 dogs with multiple acquired portasystemic shunts. Whole body reticuloendothelial function was measured by calculating the plasma clearance rate constant from a dynamic study of liver uptake of 99mTc sulfur colloid. Relative liver, spleen, and lung uptake, and a ratio of hepatic:extrahepatic uptake were measured on static equilibrium images. Results were compared with those of a group of 26 normal dogs. Compared with values for the group of normal dogs, the plasma clearance rate constant, relative liver uptake, and hepatic:extrahepatic uptake ratio were significantly decreased, and relative spleen and lung uptake were significantly increased in dogs with portasystemic shunts (P < .0001). The only significant difference between dogs with single congenital versus multiple acquired shunts was that the relative splenic uptake was higher in the former group (P < .0002). Based on these results, we concluded that dogs with portasystemic shunts have significantly impaired reticuloendothelial function. The primary cause of this dysfunction is likely a reduction in effective liver blood flow. Increases in spleen and lung reticuloendothelial activity did occur, but only partially compensated for the reduction of liver reticuloendothelial activity. Possible mechanisms for the increased spleen and lung uptake are discussed.

Pulmonary intravascular macrophages in the pathogenesis of bovine pulmonary lesions caused by Actinomyces pyogenes

Rabbit antisera raised against somatic antigens from two strains of Actinomyces pyogenes reacted specifically in a peroxidase anti-peroxidase technique which was developed for the location of the bacteria in formalin-fixed tissues. The technique was applied on experimental murine and spontaneous bovine lesions caused by A. pyogenes. By electron microscopy and immunohistochemistry it was demonstrated that pulmonary intravascular macrophages play a role in the uptake of A. pyogenes from the blood, and in the production of pyaemic pulmonary lesions.