Developmental changes in pleural liquid protein concentration in sheep

Proteomic characterization of pleural effusion, a specific host niche of Mycoplasma mycoides subsp. mycoides from cattle with contagious bovine pleuropneumonia (CBPP)

Mycoplasma mycoides subsp. mycoides (Mmm) is the causative agent of contagious bovine pleuropneumonia (CBPP), a severe pleuropneumonia in cattle. The abnormal accumulation of pleural fluid, called pleural effusion (PE), is one of the characteristics of this disease. We performed a proteomic analysis of seven PE samples from experimentally infected cattle and characterized their composition with respect to bovine and Mmm proteins. We detected a total of 963 different bovine proteins. Further analysis indicated a strong enrichment of proteins involved in antigen processing, platelet activation and degranulation and apoptosis and an increased abundance of acute phase proteins.With regard to the pathogen, up to 108 viable mycoplasma cells per ml were detected in the PE supernatant. The proteomic analysis revealed 350 mycoplasma proteins, including proteins involved in virulence-associated processes like hydrogen peroxide (H2O2) production and capsule synthesis. The bovine proteins detected will aid to characterize the inflammasome during an acute pleuropneumonia in cattle and the identified mycoplasma proteins will serve as baseline data to be compared with in vitro studies to improve our understanding of pathogenicity mechanisms. Based on our results, we named the pleural effusion an “in vivo niche” of Mmm during the acute phase of CBPP. Biological significance: This is the first study on bovine pleural effusions derived from an infectious disease and the first approach to characterize the proteome of Mycoplasma mycoides in vivo. This study revealed a high number of viable Mmm cells in the pleural effusion. The bovine pleural effusion proteome during Mmm infection is qualitatively similar to plasma, but differs with respect to high abundance of acute phase proteins. On the other hand,Mmm in its natural host produces proteins involved in capsule synthesis, H2O2 production and induction of inflammatory response, supporting previous knowledge on mechanisms underlying the survival and virulence of this pathogen while inside the natural host. This knowledge forms a profound basis for testing the identified protein candidates for diagnostics or vaccines.

Pleural liquid and its exchanges

After an account on morphological features of visceral and parietal pleura, mechanical coupling between lung and chest wall is outlined. Volume of pleural liquid is considered along with its thickness in various regions, and its composition. Pleural liquid pressure (P(liq)) and pressure exerted by lung recoil in various species and postures are then compared, and the vertical gradient of P(liq) considered. Implications of lower P(liq) in the lung zone than in the costo-phrenic sinus at iso-height are pointed out. Mesothelial permeability to H(2)O, Cl(-), Na(+), mannitol, sucrose, inulin, albumin, and various size dextrans is provided, along with paracellular "pore" radius of mesothelium. Pleural liquid is produced by filtration from parietal pleura capillaries according to Starling forces. It is removed by absorption in visceral pleura capillaries according to Starling forces (at least in some species), lymphatic drainage through stomata of parietal mesothelium (essential to remove cells, particles, and large macromolecules), solute-coupled liquid absorption, and transcytosis through mesothelium.

Transdiaphragmatic transport of tracer albumin from peritoneal to pleural liquid measured in rats

In conscious Wistar-Kyoto rats, we studied the uptake of radioactive tracer (125)I-albumin into the pleural space and circulation after intraperitoneal (IP) injections with 1 or 5 ml of Ringer solution (3 g/dl albumin). Postmortem, we sampled pleural liquid, peritoneal liquid, and blood plasma 2-48 h after IP injection and measured their radioactivity and protein concentration. Tracer concentration was greater in pleural liquid than in plasma approximately 3 h after injection with both IP injection volumes. This behavior indicated transport of tracer through the diaphragm into the pleural space. A dynamic analysis of the tracer uptake with 5-ml IP injections showed that at least 50% of the total pleural flow was via the diaphragm. A similar estimate was derived from an analysis of total protein concentrations. Both estimates were based on restricted pleural capillary filtration and unrestricted transdiaphragmatic transport. The 5-ml IP injections did not change plasma protein concentration but increased pleural and peritoneal protein concentrations from control values by 22 and 30%, respectively. These changes were consistent with a small (approximately 8%) increase in capillary filtration and a small (approximately 20%) reduction in transdiaphragmatic flow from control values, consistent with the small (3%) decrease in hydration measured in diaphragm muscle. Thus the pleural uptake of tracer via the diaphragm with the IP injections occurred by the near-normal transport of liquid and protein.

Pleural mechanics and fluid exchange

The pleural space separating the lung and chest wall of mammals contains a small amount of liquid that lubricates the pleural surfaces during breathing. Recent studies have pointed to a conceptual understanding of the pleural space that is different from the one advocated some 30 years ago in this journal. The fundamental concept is that pleural surface pressure, the result of the opposing recoils of the lung and chest wall, is the major determinant of the pressure in the pleural liquid. Pleural liquid is not in hydrostatic equilibrium because the vertical gradient in pleural liquid pressure, determined by the vertical gradient in pleural surface pressure, does not equal the hydrostatic gradient. As a result, a viscous flow of pleural liquid occurs in the pleural space. Ventilatory and cardiogenic motions serve to redistribute pleural liquid and minimize contact between the pleural surfaces. Pleural liquid is a microvascular filtrate from parietal pleural capillaries in the chest wall. Homeostasis in pleural liquid volume is achieved by an adjustment of the pleural liquid thickness to the filtration rate that is matched by an outflow via lymphatic stomata.

Normal volume and cellular contents of pleural fluid

The pleural space in healthy humans was thought to contain a few milliliters of fluid, based on extrapolation from animal studies. However, because of the obvious technical difficulties in atraumatically retrieving such a small volume of fluid, the exact volume and cellular content of human pleural fluid has not been known. Development of a minimally invasive pleural lavage technique has allowed, for the first time, the measurement of volume and cellular content of the pleural fluid in healthy humans.

Mechanical coupling and liquid exchanges in the pleural space

The pleural space provides the mechanical coupling between lung and chest wall: two views about this coupling are reported and discussed. Information on volume, composition, thickness, and pressure of the pleural liquid under physiologic conditions in a few species is provided. The Starling pressures of the parietal pleura filtering liquid into pleural space, and those of the visceral pleura absorbing liquid from the space are considered along with the permeability of the mesothelium. Information on the lymphatic drainage through the parietal pleura and on the solute-coupled liquid absorption from the pleural space under physiologic conditions and with various kinds of hydrothorax are provided.

Characterization of proteoglycans produced by rat pleural mesothelial cells in vitro

The mesothelial cell envelopes the surface of the parietal and visceral pleura. These cells are known to synthesize most of the protein constituents of the pleural basement membrane and interstitium. This study examined the ability of a rat pleural mesothelial cell line to synthesize proteoglycans in vitro. Cells were labeled with inorganic 35SO4 to label the glycosaminoglycan moiety of proteoglycans. The medium and combined cell membrane/extracellular matrix fractions contained 73 and 25% of the proteoglycan radioactivity, respectively. The medium contained a single chondroitin/dermatan sulfate proteoglycan of approximately 190 kDa, consistent with biglycan. As determined by Northern analysis of steady-state levels of messenger RNA, the cells contained message for biglycan. Stimulation of the cells with epidermal growth factor resulted in the appearance of a second chondroitin/dermatan sulfate proteoglycan of approximately 97 kDa, characteristic of decorin. The cell membrane/matrix contained a biglycan-like chondroitin/dermatan proteoglycan and several heparan sulfate proteoglycans. Pleural mesothelial cells in vitro are capable of synthesizing a variety of interstitial and basement membrane proteoglycans.