Ultrastructural observations of Pneumocystis carinii attachment to rat lung

A Molecular Window into the Biology and Epidemiology of Pneumocystis spp

Pneumocystis, a unique atypical fungus with an elusive lifestyle, has had an important medical history. It came to prominence as an opportunistic pathogen that not only can cause life-threatening pneumonia in patients with HIV infection and other immunodeficiencies but also can colonize the lungs of healthy individuals from a very early age. The genus Pneumocystis includes a group of closely related but heterogeneous organisms that have a worldwide distribution, have been detected in multiple mammalian species, are highly host species specific, inhabit the lungs almost exclusively, and have never convincingly been cultured in vitro, making Pneumocystis a fascinating but difficult-to-study organism. Improved molecular biologic methodologies have opened a new window into the biology and epidemiology of Pneumocystis. Advances include an improved taxonomic classification, identification of an extremely reduced genome and concomitant inability to metabolize and grow independent of the host lungs, insights into its transmission mode, recognition of its widespread colonization in both immunocompetent and immunodeficient hosts, and utilization of strain variation to study drug resistance, epidemiology, and outbreaks of infection among transplant patients. This review summarizes these advances and also identifies some major questions and challenges that need to be addressed to better understand Pneumocystis biology and its relevance to clinical care.

Fundamental technical elements of freeze-fracture/freeze-etch in biological electron microscopy

Freeze-fracture/freeze-etch describes a process whereby specimens, typically biological or nanomaterial in nature, are frozen, fractured, and replicated to generate a carbon/platinum "cast" intended for examination by transmission electron microscopy. Specimens are subjected to ultrarapid freezing rates, often in the presence of cryoprotective agents to limit ice crystal formation, with subsequent fracturing of the specimen at liquid nitrogen cooled temperatures under high vacuum. The resultant fractured surface is replicated and stabilized by evaporation of carbon and platinum from an angle that confers surface three-dimensional detail to the cast. This technique has proved particularly enlightening for the investigation of cell membranes and their specializations and has contributed considerably to the understanding of cellular form to related cell function. In this report, we survey the instrument requirements and technical protocol for performing freeze-fracture, the associated nomenclature and characteristics of fracture planes, variations on the conventional procedure, and criteria for interpretation of freeze-fracture images. This technique has been widely used for ultrastructural investigation in many areas of cell biology and holds promise as an emerging imaging technique for molecular, nanotechnology, and materials science studies.

Management of Pneumocystis Jirovecii pneumonia in HIV infected patients: current options, challenges and future directions

The discovery of the Human Immunodeficiency Virus (HIV) was led by the merge of clustered cases of Pneumocystis jirovecii Pneumonia (PCP) in otherwise healthy people in the early 80’s.1,2 In the face of sophisticated treatment now available for HIV infection, life expectancy approaches normal limits. It has dramatically changed the natural course of HIV from a nearly fatal infection to a chronic disease.3–5 However, PCP still remains a relatively common presentation of uncontrolled HIV. Despite the knowledge and advances gained in the prevention and management of PCP infection, it continues to have high morbidity and mortality rates. Trimethoprim-sulfamethoxazole (TMP-SMZ) remains as the recommended first-line treatment. Alternatives include pentamidine, dapsone plus trimethoprim, clindamycin administered with primaquine, and atovaquone. For optimal management, clinicians need to be familiar with the advantages and disadvantages of the available drugs. The parameters used to classify severity of infection are also important, as it is well known that the adjunctive use of steroids in moderate to severe cases have been shown to significantly improve outcome. Evolving management practices, such as the successful institution of early antiretroviral therapy, may further enhance overall survival rates.

Alveolar damage in AIDS-related Pneumocystis carinii pneumonia

OBJECTIVE

Pneumocystis carinii pneumonia is the most common and serious of the pulmonary complications of AIDS. Despite this, many basic aspects in the pathogenesis of HIV-associated P carinii pneumonia are unknown. We therefore undertook a light and electron microscopic study of transbronchial biopsy specimens to compare pathologic features of P carinii pneumonia and other HIV-related lung diseases.

DESIGN AND PATIENTS

Thirty-seven consecutive HIV-infected patients undergoing a diagnostic bronchoscopy.

RESULTS

P carinii pneumonia was characterized by an increase in inflammation, edema, exudate, fibrosts, type II pneumocyte proliferation, and cellular infiltration of the alveolar wall when compared with other lung diseases (all p < 0.05). Electron microscopy showed apposition of the trophozoite to the type I pneumocyte. Erosion of type I pneumocytes was observed in 13 of 15 patients with P carinii pneumonia, whereas none without P carinii pneumonia had this finding (p < 0.05). Erosion of the type II pneumocyte was not observed.

CONCLUSION

Inflammation, interstitial fibrosis, and alveolar epithelial erosion are characteristic features of P carinii pneumonia. The changes may form the pathologic basis for the respiratory failure seen in patients with P carinii pneumonia. Electron microscopy did not show any diagnostie advantage over conventional light microscopy using routine stains.

Pneumocystis carinii: an atypical fungal micro-organism

The purpose of this review is to assist mycologists in having a better understanding of Pneumocystis carinii and the disease that it causes. Now considered to be a fungus, P. carinii is unusual in its life cycle and relationship with the host. P. carinii pneumonia (PCP) pathogenesis, immunology and host defence mechanisms are examined, as well as epidemiological and control strategies. Most pneumocystosis pathophysiological changes result from the parasite's attachment and proliferation in the lungs, resulting in a filling of the alveoli with masses of the micro-organism. Pathological changes include an increase in alveolar capillary membrane permeability and injury to the alveolar epithelium, which may be mediated by the release of degradative enzymes from the pathogen. A host response takes place by hypertrophy, and hyperplasia involving type II epithelial alveolar cells. P carinii interacts with pulmonary surfactants by binding to the hydrophilic proteins A and D, and by modifying their phospholipid composition. Alveolar macrophages and CD4+ T cells play a key role in the host's defence against Pneumocystis. The epidemiology of PCP remains poorly understood. Airborne transmission has been established, but the actual infective form and its source remains unknown. Studies concerning P. carinii genetic diversity have shown that the parasite polymorphism is related, at least partially, to the host species. A strong host-species specificity in P. carinii has been found. From an epidemiological perspective, there appears to be no animal reservoir for the agent of human PCP. Thus, this disease should not be considered to be zoonotic. Although a significant decrease in the incidence of pneumocystosis has been obtained when employing chemoprophylaxis, anti-P. carinii drugs are not completely successful, often inducing deleterious side-effects. For these reasons, new prophylactic and therapeutic strategies need to be developed. One approach could be based on the anti-P. carinii effect of yeast killer toxins and antibiotic anti-idiotypic antibodies.

Pneumocystis carinii attachment increases expression of fibronectin-binding integrins on cultured lung cells

Pneumocystis carinii is an extracellular pathogen which requires attachment to alveolar epithelial cells for growth and replication. Previous studies have demonstrated that the extracellular matrix protein fibronectin (Fn) facilitates attachment of P. carinii to lung cells. This study addresses the role of cell surface Fn receptors (integrins) as mediators of P. carinii attachment and demonstrates the effect of P. carinii attachment on integrin expression on cultured lung cells. To determine the role of Fn-binding integrins in P. carinii attachment, attachment of 51Cr-labelled P. carinii organisms to the lung epithelial cell line A549 was quantified in the presence or absence of anti-integrin antibodies. Antibodies to the alpha v and alpha 5 integrin subunits significantly inhibited P. carinii attachment, while addition of antibody to the alpha subunit of a non-Fn-binding integrin, alpha 2, did not affect P. carinii attachment. To further investigate the role of Fn-binding integrins in P. carinii attachment, the effect of P. carinii attachment on expression of the alpha v and alpha 5 integrin subunits was determined. A549 cells incubated with either P. carinii organisms or with the P. carinii major surface glycoprotein gp120 demonstrated a 3- to 10-fold increase in expression of the alpha 5 integrin subunit; however, neither P. carinii nor gp120 affected the expression of alpha v integrin. Furthermore, the effects of P. carinii on A549 cell alpha 5 integrin expression were attenuated by the addition of an anti-gp120 antibody which blocks P. carinii attachment to A549 cells. Therefore, P. carinii attachment to lung epithelial cells appears to be mediated by alpha v- and alpha 5-containing integrins expressed on the epithelial cell surface, and P. carinii attachment results in increased expression of the alpha 5 integrin subunit.

Incorporation of fatty acids and amino acids by cultured Pneumocystis carinii

Cultured P. carinii rapidly took up a variety of fatty acids. The relative rates of uptake for four fatty acids were 18:1 >> 16:0 approximately equal to 18:0 approximately equal to 18:2. Fatty acids were primarily incorporated into phospholipids and the uptake process was specifically inhibited by 2.2 and 22 microM primaquine, a concentration having no effect on host cells. Amino acids were also taken up by cultured P. carinii in a primaquine sensitive process. Radiolabeled leucine was incorporated into the major surface glycoprotein of P. carinii. The formation of radioactive P. carinii-specific proteins indicated that the cultured organisms carried out transcription and translation and that the incorporation of amino acids was dependent upon P. carinii rather than rare HEL human embryonic lung cells. The spinner flask culture system provides convenient access to P. carinii for metabolic studies in defined medium for a period of 5-14 days after inoculation.

The yeast killer phenomenon: a hypothetical way to control Pneumocystis carinii pneumonia

Pneumocystis carinii is an important agent of pneumonia in immunocompromised individuals, especially in acquired immunodeficiency syndrome AIDS patients P. carinii attaches specifically to type 1 pneumocytes. Although this phenomenon must play a marked role in pneumocystosis pathophysiology, no therapeutic molecules able to inhibit specifically the parasite attachment were found. A killer toxin, secreted by the yeast Pichia anomala, induced a significant decrease in P. carinii in vitro attachment and inhibited the parasite infectivity in SCID mice. Killer toxins cannot be used as systemic antibiotics. However, it was possible to produce antiidiotypic antibodies against a monoclonal antibody specific of the toxin active site. These antilds were shown to mimic the in vitro killer effect for the toxin and were called 'antibiobodies'. The susceptibility of P. carinii to the antimicrobial activity of the killer toxin made it possible to hypothesize that the killer phenomenon could constitute a new way for the treatment and prophylaxis of P. carinii infections.

Ultrastructural observation of Pneumocystis carinii in bronchoalveolar lavage fluid from non-AIDS patients with P carinii pneumonia

To investigate the morphology of Pneumocystis carinii in vivo, we studied the ultrastructure of P carinii in bronchoalveolar lavage fluid (BALF) obtained from four non-AIDS patients with P carinii pneumonia (PCP), and observed the morphologic changes after treatment in one patient. Every form recognized in the normal life cycle of P carinii, ie, thick-walled cysts, crescent-shaped cysts, and trophozoites, was detected in the pretreatment BALF specimens. In the posttreatment BALF, P carinii revealed marked ultrastructural changes such as the elongation of thick-walled cysts, the degeneration of intracystic bodies, and the disappearance of trophozoites. Massive debris derived from P carinii was still found in the BALF even after the treatment. Examination of P carinii in BALF, including ultrastructural observations, might help us to evaluate the disease status and the effect of treatment in patients with PCP.

Nude rats as a model of natural Pneumocystis carinii pneumonia: sequential morphological study of lung lesions

A spontaneous infection with Pneumocystis carinii (P.c.) caused enzootic fatal pneumonia in a long-term experiment with athymic Rowett Nude (Han:RNU rnu/rnu) and New Zealand Nude (Han:NZNU rnuN/rnuN) rats. In order to reproduce the infection and to characterize the early pathogenesis of lung lesions, 13 young athymic Han:RNU and Han:NZNU rats from P.c.-free breeding colonies were housed together in one room with chronically P.c.-infected rats. They were killed after 8, 12, 16, 20 or 24 weeks, and their lungs were examined for P.c. infection by means of light microscopy, immunohistochemistry and transmission electron microscopy. Lung lesions progressed from a mild interstitial pneumonia with scattered alveolar macrophages (8 weeks) to a severe diffuse interstitial pneumonia with widespread areas of distended alveoli, filled with foamy material. In all lungs, P.c. antigen was detected immunohistochemically, developing from small intra-alveolar aggregations of organisms into large multifocal clusters. Ultrastructurally, P.c. trophozoites and cysts were seen attached to type I pneumocytes and lying free in the alveolar lumen. Chronic severe P.c. pneumonia (20 and 24 weeks) was characterized by masses of P.c. trophozoites in the alveoli and alveolar walls, extensive proliferation of type II pneumocytes and interstitial fibrosis. The easy and consistent horizontal transmission of spontaneous P.c. pneumonia to previously non-infected athymic Han:RNU and Han:NZNU rats and the similarity of the disease to human infection demonstrate both rat strains to be excellent models for studying pulmonary pneumocystosis of immunodeficient human patients.

Influence of Pneumocystis carinii pneumonia on serum and tissue concentrations of pentamidine administered to rats by tracheal injections

Pentamidine isethionate was administered by the tracheal route to control rats and immunodepressed rats with Pneumocystis carinii pneumonia (PCP). The serum concentration of pentamidine base 20 min after the administration was higher in the PCP rats (309 +/- 165 ng/ml) than in the control animals (71 +/- 36 mg/ml; p less than 0.001); 90 min after the injection the proportion of the pentamidine administered was lower in the right lung of the PCP rats (29 +/- 15%) than in the control rats (57 +/- 23%; p = 0.038); the proportion of pentamidine in the left kidney was higher in the PCP rats (14 +/- 4%) than in the control animals (4 +/- 2%; p less than 0.001). Respiratory clearance of 99mTc-DTPA, an index of the permeability of the respiratory epithelium, was higher in the PCP rats (1.84 +/- 0.42 %/min) than in the controls (0.44 +/- 0.11 %/min; p less than 0.001). We conclude that the more rapid diffusion of pentamidine from the alveolar lumen to the pulmonary circulation is explained by the increased alveolocapillary permeability as a result of pneumocystosis.

Is Pneumocystis carinii a deep mycosis-like agent?

Pneumocystis carinii is a widespread eukaryotic microorganism found in the lungs of healthy mammals, including humans. It is able to proliferate extensively in the alveoli, becoming an important agent of severe pneumonitis in immunosuppressed hosts, especially in persons suffering from AIDS. The taxonomic position of P. carinii is uncertain. Typical cytoplasmic organelles of eukaryotic cells have been found and described in the parasite. Biochemical research is hindered by the lack of an efficient in vitro culture system. Results of comparative study of nucleic acid sequences suggest that Pneumocystis is a fungus. However, ultrastructural, biochemical and nucleic acid homology insights appear as clearly insufficient to class Pneumocystis. Pneumocystis infection might be acquired, as deep mycoses, from environmental sources through the respiratory tract. Thus, the hypothesis of an environmental stage of the parasite must be considered. Pneumocystis might be seen as a widespread pathogenic dimorphous fungus. As fungal agents, P. carinii is able to disseminate from the infected lung to other organs. However, deep mycoses and pneumocystosis induce different histopathological changes in the host. Furthermore, deep fungal infections, unlike pneumocystosis, cannot be transmitted from one infested host to another one. Beside these two aspects, pneumocystosis shares many features with deep mycoses. Research on the epidemiology of pneumocystosis is needed.

Serum carcinoembryonic antigen: a prognostic marker in HIV-related Pneumocystis carinii pneumonia

Serum concentrations of carcinoembryonic antigen (CEA) were measured in 43 consecutive patients with HIV-related Pneumocystis carinii pneumonia (PCP). The subjects were divided into 2 groups according to the severity of the PCP:PaO2 in ambient air (AA) less than or equal to 50 mmHg on admission (n = 22, group 1) and PaO2 greater than 50 mmHg (n = 21, group 2). In addition, 57 HIV patients with either non-PCP pulmonary diseases (n = 34, group 3) or extrapulmonary disease (n = 23, group 4) were studied. Mean CEA levels (ng/ml) were 13 +/- 10 in group 1 and 4.9 +/- 5.5 in group 2 (p less than 0.001). The corresponding values in groups 3 and 4 were much lower (2.7 +/- 1.8 and 2.4 +/- 1.8, respectively). In group 1, mean initial CEA levels were higher (p less than 0.001) in the patients who died (n = 6; 23.5 +/- 11) than in the survivors (n = 16; 8.9 +/- 7), although the initial mean PaO2 were identical (39 +/- 7 and 39 +/- 8 mmHg, respectively) and the initial mean LDH levels were not significantly different (1544 +/- 530 and 1200 +/- 457 IU/l). CEA levels fell during specific anti-PCP therapy associated with corticosteroids but returned to normal only in the survivors. We conclude that CEA levels are increased in patients with PCP and acute respiratory distress. Among the patients with PaO2 levels of less than or equal to 50 mmHg before treatment, only high levels of CEA (greater than 20 ng/ml) were associated with a fatal outcome, regardless of anti-PCP therapy associated with corticosteroids.(ABSTRACT TRUNCATED AT 250 WORDS)

High osmotic pressure enables fine ultrastructural and cytochemical studies on Pneumocystis carinii. I. Epon embedding

High osmotic pressure was used to preserve the ultrastructure of rabbit-, SCID mouse-, and rat-derived Pneumocystis carinii organisms from osmotic stress during fixation. Organelles and cytosol were well preserved within the tonicity range of 850-1,300 mosmol. Under these experimental conditions, we determined that the endoplasmic reticulum was well developed in all parasite stages and could observe the Golgi complex, autophagic vacuoles, dense bodies, type II endoplasmic saccules, and the recently described outer surface membrane, which was found in all parasite stages. The biological implications of these findings are discussed.

Pneumocystis carinii attachment to cultured lung cells by pneumocystis gp 120, a fibronectin binding protein

Pneumocystis carinii is an extracellular organism which is thought to require attachment to alveolar epithelial cells for its growth and replication in humans. Fibronectin (Fn) binding to P. carinii is essential for optimal P. carinii attachment. This study demonstrates that gp120, a 110-120-kD membrane glycoprotein on P. carinii, mediates attachment of the organism to cultured lung cells and is the site of Fn binding to P. carinii. A 51Cr-labeled P. carinii binding assay was used to quantify attachment of the organism to the alveolar epithelial cell line A549. Addition of free gp120, purified from whole P. carinii organisms, caused a significant decrease in attachment of P. carinii to A549 cells from 44.2 +/- 5.5% to 22.4 +/- 4.2% (P less than 0.01). Preincubation of the P. carinii organisms with a polyclonal antibody to gp120 also resulted in a marked decrease in P. carinii attachment to A549 cells from 46.8% +/- 5.2% to 21.3 +/- 4.8% (P less than 0.01). Furthermore, addition of free gp120 to P. carinii organisms caused a significant reduction in specific binding of 125I-Fn to P. carinii (from 83.3 +/- 8.5 ng to 47.1 +/- 5.9 ng, P less than 0.01). Similarly, anti-gp 120 antibody decreased specific Fn binding to P. carinii from 74.3 +/- 8.4 ng to 25.5 +/- 5.3 ng (P less than 0.001). Solubilized P. carinii organisms separated by gel electrophoresis and blotted with 125I-Fn demonstrated specific binding of the 125I-Fn to gp120. In addition, a specific anti-beta 1-integrin antiserum reacted with gp120 by Western blot, suggesting structural homology between gp120 and the beta-subunit of integrins. Thus, the data suggest that the P. carinii membrane glycoprotein gp120 functions as a Fn binding protein and is required for optimal P. carinii attachment to alveolar epithelial cells.

Pneumocystis carinii pneumonia in simian immunodeficiency virus infection: immunohistological and scanning and transmission electron microscopical studies

Pneumocystis carinii pneumonia occurred in 6 of 17 rhesus monkeys infected with simian immunodeficiency virus and was studied by immunohistochemistry and by scanning and transmission electron microscopy. A monoclonal antibody/streptavidin-biotin-peroxidase staining method was highly sensitive for detecting the organisms in small, early lesions and was much more sensitive and specific than traditional silver impregnation methods. Reprocessing of paraffin wax-embedded lung tissue for scanning electron microscopy and use of a video printer to produce a photographic montage of light microscopic lesions allowed the same areas of tissue to be examined and compared by both methods. The ultrastructural morphology of P. carinii in the rhesus monkey was identical to that in man, as were the histological and electron microscopic lesions, including pulmonary fibrosis. Trophozoites were seen attached to alveolar type I epithelium mainly by intimate apposition to the plasma membrane, but scanning electron microscopy also showed attachment by elongated filopodia. Few macrophages were present in infected alveoli, and though phagocytosis followed by digestion of P. carinii trophozoites was observed, it appeared to occur at a very low level.

Continuous positive airway pressure ventilation for respiratory failure associated with Pneumocystis carinii pneumonia

The value of continuous positive airway pressure (CPAP) ventilation via a tight fitting face mask was assessed in eight HIV-1 antibody-positive patients with Pneumocystis carinii pneumonia who were in hypoxaemic respiratory failure. All patients were conscious, able to protect their airway and not hypercapnic. Treatment was effective in seven patients. Prior to CPAP, mean (range) arterial oxygen tension was 6.7 (4.7-10.5) kPa in seven patients breathing oxygen via a face mask (FiO2 = 0.6), 6.1 kPa in one patient breathing room air and rose to 9.9 (6.8-12.8) kPa with CPAP (FiO2 = 0.6 and PEEP = 1.3 kPa in six patients and 2.6 kPa in one patient); the mean increase in PaO2 was 3.1 kPa (P less than 0.02). These seven patients experienced a rapid reduction in dyspnoea and their respiratory rate fell from a mean of 40 breaths min-1 to 32 breaths min-1 (P less than 0.001). One patient deteriorated rapidly on CPAP and died: no other complications were seen with this technique. CPAP was continued for a mean of 4.5 days and the seven responders all survived the episode of P. carinii pneumonia. We conclude that mask CPAP provides an effective means of improving oxygenation in severely hypoxaemic patients with P. carinii pneumonia.

Biodistribution, tissue reaction, and lung retention of pentamidine aerosolized as three different salts

Aerosolized pentamidine isoethionate is retained in the lung and appears to prevent Pneumocystis carinii pneumonia (PCP) in many AIDS patients. We evaluated alternative formulations of pentamidine that might reduce the airway irritation associated with aerosolized pentamidine isoethionate. Specifically, we assessed the biodistribution, histologic response, and lung retention of the isoethionate, gluconate, and lactate salts of pentamidine after aerosol administration to mice. For each of the three aerosolized salts tested, greater than 50% of the pentamidine initially recovered from the lungs after one dose was still retained there 14 days later. Thus, significant levels of pentamidine, aerosolized as three different salts, are retained in the lung for at least 2 wk after a single dose. The three salts of pentamidine each produced high lung to extrapulmonary drug ratios, the converse of that produced by intravenous injection of pentamidine isoethionate. At very high aerosol doses, the ability of the lung to retain pentamidine appeared saturable. Even aerosolized daily for 2 wk at very high doses, none of the three pentamidine salts produced histologic evidence of organ toxicity. A Phase 1 trial of aerosolized pentamidine gluconate in AIDS-PCP patients is now in progress to determine if this approach can reduce airway irritation.

Pulmonary disease in AIDS patients

Pulmonary disease remains a major complication of the human immunodeficiency virus (HIV). Over the past decade several changes in the pattern of disease have occurred. Pneumocystis carinii pneumonia (PCP) remains the most common opportunistic pathogen in AIDS patients, though its incidence on bronchoscopy has declined and empiric therapy often occurs without a specific diagnosis. Changes in the management of patients with PCP have included different dosages and routes of administration for chemotherapy, improved overall survival, and a recent increase in the number of patients surviving episodes of respiratory failure. In addition, infection with mycobacteria tuberculosis (M.Tb.) has emerged as a major public health problem. The pattern of M.Tb. is distinct from non-immunocompromised patients though response to therapy usually occurs.

Pneumocystis carinii: inhibition of lung cell growth mediated by parasite attachment

Pneumocystis carinii pneumonia is a significant cause of mortality in immunocompromised patients. Current concepts suggest that attachment of P. carinii to alveolar epithelium is required for development of pneumonia. We examined the mechanism of P. carinii adherence to cultured A549 cells, a permanent cell line derived from human alveolar epithelium. P. carinii adherence was quantified by measuring attachment of 51Cr-labeled P. carinii to cultured A549 cells. After 8 h of incubation, 37.4 +/- 4.2% of P. carinii were adherent to A549 cells. In the presence of agents known to impair cytoskeletal function, including 10(-5) M cytochalasin B, 10(-5) M colchicine, and 10(-5) M trimethylcolchicinic acid (TMCA), adherence was decreased from 57.4 +/- 4.2% to 9.3 +/- 3.4%, 12.5 +/- 3.6%, and 21.5 +/- 3.6%, respectively (P less than 0.01, all comparisons). Secondly, we examined the effect of P. carinii on the function of A549 cells. P. carinii resulted in significant impairment of A549 cell growth, indicating P. carinii adversely affected the function of target lung cells. A P. carinii:A549 cell ratio of 50:1 resulted in 43.5 +/- 2.9% inhibition of A549 cell growth (P less than 0.001). Additionally, TMCA, which significantly prevented attachment of P. carinii, reversed the impairment of A549 cell growth. These data demonstrate that P. carinii attachment to cultured lung cells can be quantified, is dependent on intact cytoskeletal function and is necessary for impairment of lung cell replication.

Role of fibronectin in Pneumocystis carinii attachment to cultured lung cells

Attachment of pathogens to host cells is a prerequisite for the development of many infections. Pneumocystis carinii (PC) pneumonia is characterized by attachment of PC trophozoites to the alveolar epithelium. The mechanism of this process is unknown. Fibronectin (Fn) is a glycoprotein present in the alveolar space known to mediate cell-cell attachment, including the attachment of certain pathogens to host epithelial cells. In this study the binding of Fn to PC trophozoites has been characterized in vitro using 125I-Fn. Fn binds saturably and specifically to 6.4 x 10(5) binding sites per organism with an apparent binding constant, Kd, of 1.2 x 10(-8) M. Fn binding to PC was inhibited by the addition of Arg-Gly-Asp-Ser (RGDS), a tetrapeptide containing the active site of the cell-binding domain of Fn. PC attachment to an alveolar epithelial cell line was quantified using 51Cr-labeled PC trophozoites. Attachment was decreased from 24 +/- 1.9% to 12.1 +/- 1% (P less than 0.01) by the addition of an anti-Fn antibody, an effect that could be overcome by the addition of excess free Fn. It is concluded that binding of Fn to PC may be an important initial step in the attachment of the organism to alveolar epithelial cells. Furthermore, it appears that PC recognizes and binds to the RGDS cell attachment site of Fn.

Silver staining of Pneumocystis carinii in the rat's lung

The backscattered electron imaging mode of the scanning electron microscope was used to study the ontogenetic acquisition of argyrophilia in Pneumocystis carinii in rats. Silver staining continually increased from the late trophozoite to the mature cyst stage. The silver uptake began with a fine outline at the surface of the bodies of the late trophozoites; their cellular extensions, however, did not stain. The oblate precyst forms acquired the silver in heterogeneous patches. On spherical cysts the silver staining became more uniform and intense with at least one dense spot. The spherical and collapsed cysts also had short silver staining projections that may represent microvilli. Collapsed forms were paler than spherical ones and appear to be cysts that have undergone partial or complete release of sporozoites. These cell surface observations confirm and amplify previous transmission electron microscopical and histochemical studies indicating that silver staining correlates with the acquisition of the cell pellicle.

Alveolar-capillary block in patients with AIDS and Pneumocystis carinii pneumonia

To determine the value of subdividing diffusing capacity for carbon monoxide (DL) in diagnosing and monitoring the course of Pneumocystis carinii pneumonia (PCP), we measured DL, membrane diffusing capacity (DM), and pulmonary capillary blood volume (VC) in 20 control subjects, 20 patients with a low DL (less than 75% predicted) and newly diagnosed PCP, and 16 patients with a low DL in most of whom PCP had been suspected and excluded. Ten patients with PCP were restudied approximately 60 days after treatment. When clinically indicated, lung biopsies were obtained for histologic examination. Compared with mean values in control subjects (DL = 92%, DM = 101%, and VC = 35 ml/m2), all values were decreased (p less than 0.01) in patients with PCP (DL = 58%, DM = 33%, and VC = 26 ml/m2) and in those without PCP (DL = 61%, DM = 56%, and VC = 22 ml/m2). Values of DM were significantly less (p less than 0.05) in patients with, than in those without, PCP. Analysis of lung biopsies by light and electron microscopy showed overlapping morphologic abnormalities in the 2 groups of patients. In the 10 patients with PCP restudied after successful treatment, the mean DL increased from 60 to 80% (p less than 0.0005), the DM increased from 35 to 108% (p less than 0.006), and the VC did not change. These results suggest that in contrast to most disorders in which DL is decreased, PCP causes reversible alveolar-capillary block.

Successful treatment with aerosolized pentamidine of Pneumocystis carinii pneumonia in rats

We examined both the therapeutic efficacy and tissue distribution of aerosolized pentamidine in immunosuppressed rats with Pneumocystis carinii pneumonia. In rats immunosuppressed by 5 weeks of pretreatment with dexamethasone, a 2-week course of 5 mg of aerosolized pentamidine per kg per day, administered free or encapsulated in the drug carrier system (liposomes), eradicated P. carinii pneumonia in 75% of treated animals. At this dose, extrapulmonary drug uptake as measured by a sensitive high-pressure liquid chromatography assay was negligible. No significant differences in tissue distribution were noted between aerosolized free and liposome-encapsulated pentamidine. In rats receiving dexamethasone for 6 weeks prior to treatment with pentamidine, both lung uptake and therapeutic efficacy of aerosolized pentamidine (5 mg/kg per day) were substantially reduced. Aerosolized pentamidine appears to be an effective therapy for P. carinii pneumonia in rats and produces significantly lower extrapulmonary drug deposition than parenteral administration. The severity of P. carinii involvement at the time of treatment influences both the level of drug delivery to the lung and the response to aerosolized pentamidine therapy.