Advances in pneumocystis biology

Prophylactic effect of FK463, a novel antifungal lipopeptide, against Pneumocystis carinii infection in mice

The prophylactic effect of FK463, a new water-soluble echinocandin-like lipopeptide with inhibitory activity against 1, 3-beta-D-glucan synthase, against Pneumocystis carinii infection was investigated with the severe combined immunodeficient (SCID) mouse model. Treatment with FK463, pentamidine, and saline only was performed for 6 weeks from the day after the SCID mice were inoculated intranasally with infected lung homogenates. FK463 at 0.2 or 1.0 mg/kg of body weight, pentamidine at 4 mg/kg, or saline was subcutaneously administered daily into the backs of the SCID mice. The effects of the drugs were evaluated by detection of P. carinii cysts in mouse lung homogenates by toluidine blue O staining, lung histology, and PCR amplification of a P. carinii-specific DNA fragment from the lungs. P. carinii cysts were detected in the lungs of all mice administered saline. In contrast, no cysts were detected in mice administered both doses of FK463 and pentamidine. A specific DNA fragment was amplified from all mice administered saline and at least half or more of the mice administered FK463 and pentamidine. These results indicate that FK463 acts on cyst wall formation but not on trophozoite proliferation and is extremely effective in preventing P. carinii-associated pneumonia. These results suggest that FK463 is potentially useful as a prophylactic agent against P. carinii infection.

EB9, a new antibody for the detection of trophozoites of Pneumocystis carinii in bronchoalveolar lavage specimens in AIDS

AIM

To prepare a monoclonal antibody (EB9) against the trophozoite form of Pneumocystis carinii and to test its efficacy for detecting infection with this organism.

METHOD

The sensitivity and specificity of the EB9 antibody were assessed by comparing it with other conventional stains (Papanicolaou, Giemsa and Grocott) and 3F6 antibody in 33 bronchoalveolar lavage specimens from HIV positive patients suspected of having P carinii pneumonia.

RESULTS

P carinii infection was detected in 15 of 33 patients. In 14 cases the organism was detected by two or more of the staining methods used; however, EB9 failed to detect infection in two cases which were positive by other staining techniques. In one case P carinii infection was detected by EB9 only.

CONCLUSION

The results of this study suggest that P carinii infection in the lung may occur in two forms: the cyst form and the trophozoite form, which may explain the observed variation in response to treatment.

Genetic stability and diversity of Pneumocystis carinii infecting rat colonies

There is increasing molecular and antigenic evidence that Pneumocystis carinii organisms isolated from humans, ferrets, and rats are different species. In contrast, little is known about the extent of genetic diversity among P. carinii strains found within a single mammalian species. In the present study, electrophoretic karyotypes were obtained from P. carinii prepared from 10 chronically immunosuppressed rat colonies to investigate diversity at the chromosomal level. Most organism preparations produced patterns with 13 to 15 bands, but as many as 24 bands were observed in a few preparations. All bands separated between 700 and 300 kbp. Four distinct karyotype forms emerged from among the 13- to 15-band karyotypes of the 10 colonies sampled. Form 1 was shared by five rat strains from two vendors; form 2 was shared by two rat strains from the same vendor; and forms 3 and 4 were unique to their vendor colonies. Within a given rat colony, most rats harbored the same P. carinii karyotype. A survey of selected rat colonies showed that the karyotype within a vendor colony could remain stable over a period of 2 to 3 years. Hybridization of the blotted karyotypes with a repetitive DNA element isolated from rat-derived P. carinii and with single-copy gene probes showed that every chromosome in the karyotypes contained some repetitive DNA, and there was a general size concordance among the chromosomes carrying the unique gene loci. Differences in gene sequences, electrophoretic karyotypes, and hybridization profiles suggested that the immunosuppressed rats were infected by genetically distinct P. carinii strains. A provisional system of nomenclature for P. carinii that will permit differentiation of P. carinii organisms from the same mammalian host is discussed. These data show that all rats were not infected by a single type of P. carinii, that pulsed-field gradient electrophoresis can detect sufficient genetic diversity among the organism preparations to allow for characterization of the organisms, and that the genome of the organism within the rat host is relatively stable over time.

Evidence for two genetic variants of Pneumocystis carinii coinfecting laboratory rats

Pneumocystis carinii pneumonia is an oftentimes fatal infection for hosts in an immunocompromised state. The disease occurs in a wide variety of mammals, but the etiologic agent of this disease has been referred to as P. carinii regardless of the host species. However, even within a single host species, such as laboratory rats, distinct varieties of P. carinii have been identified from differences in the electrophoretic migration of chromosomes in agarose gels. Here we present evidence indicating that some laboratory rats can contain two different genetic variants of P. carinii that differ not only in electrophoretic karyotype but also in the presence of a particular repeated DNA sequence, in the presence of an intron in the 18S ribosomal RNA gene, and in the sequence of part of the 18S rRNA gene. Most of the rat colonies studied were infected with P. carinii that contained the repeated DNA and the 18S rRNA gene intron. The other type of rat-derived P. carinii, which lacked the repeated DNA and the intron in the 18S rRNA gene, was found as a coinfection with the first. Parasite populations from different coinfected rats contained the two variants in different proportions.

Use of the UV ParaLens adapter as an alternative to conventional fluorescence microscopy for detection of Pneumocystis carinii in direct immunofluorescent monoclonal antibody-stained pulmonary specimens

The UV ParaLens light microscope adapter offers a useful and cost-effective alternative to conventional fluorescence microscopy for Pneumocystis carinii identification, particularly in AIDS patients. In a blinded study, in which 153 pulmonary specimens were examined for P. carinii by direct immunofluorescence, 40 of 42 specimens positive by fluorescence microscopy were also positive by ParaLens. No false positives were observed.

Application of 3-d computer-aided reconstruction in parasitology

Three-dimensional (3-D) reconstruction is sometimes useful to describe the fine morphology of the subcellular organization of parasites. Francois Polluoult, Bruno Pietrzyk, Eduardo Dei-Cas and Daniel Camus show how computer-aided reconstruction from serial sections is done.

Analysis of Pneumocystis carinii cyst wall. I. Evidence for an outer surface membrane

It has long been thought that the cyst form of Pneumocystis carinii, which can resist host defenses and antimicrobial drugs, is responsible for relapses of P. carinii pneumonia. The thick wall of the cyst is immunogenic and rich in glucosyl/mannosyl and N-acetyl-D-glucosamine residues. In this study we have demonstrated the presence of a hitherto unreported outer membrane in the cyst wall of P. carinii. This membrane was detected by a combination of techniques, including transmission electron microscopy, freeze-fracture electron microscopy, and membrane labeling with fluorescent lipid analogs following treatment of P. carinii cysts from infected rats for 30 min with Zymolyase, a beta-1-3 glucanase. As in gram-negative bacteria and blue-green algae, this 2nd membrane may have an important role in osmoregulation and nutrient utilization; it may also mediate the interaction of P. carinii with its host and serve as a target for drug therapy.

Phylogenetic association of Pneumocystis carinii with the 'Rhizopoda/Myxomycota/Zygomycota group' indicated by comparison of 5S ribosomal RNA sequences

The cytoplasmic 5S ribosomal RNA (5S rRNA) sequence from Pneumocystis carinii was determined. A sequence comparison matrix of 382 eukaryote 5S rRNA sequences and an evolutionary tree were constructed to establish the phylogenetic position of Pneumocystis. The data suggest that Pneumocystis is associated with the Rhizopoda/Myxomycota/Zygomycota group (= 'Protista fungi') but not with common fungi, such as Ascomycota or Basidiomycota, nor with other protozoa.

Yeast glucan in the cyst wall of Pneumocystis carinii

Ultrastructurally, the cyst wall of Pneumocystis carinii consists of an electron-dense outer layer, an electron-lucent middle layer, and an innermost plasmalemma. This is similar in appearance to the cell wall of some yeasts, e.g. Saccharomyces cerevisiae, which consists of an outer dense layer of mannan, a middle lucent layer of beta-1,3-glucan (yeast glucan) and an innermost plasmalemma. The cyst wall of P. carinii, as well as the cell wall of S. cerevisiae, can be labeled by a variety of methods which stain polysaccharides, such as Gomori's methenamine silver (GMS) and by Aniline blue, a dye which selectively stains beta-1,3-glucan. The treatment of P. carinii cysts with Zymolyase, which the key enzyme is beta-1,3-glucan laminaripentaohydrolase, results in lysis of the outer 2 layers of the cyst wall and the loss of positive staining by both GMS and Aniline blue. The lysis of elements of the cyst wall of P. carinii is achieved under the same conditions and concentration at which Zymolyase lyses the outer 2 layers of the cell wall of viable cells of S. cerevisiae. These observations indicate that a major component of the cyst wall of P. carinii is beta-1,3-glucan.

Detection of Pneumocystis carinii in lung-derived samples using monoclonal antibodies to an 82 kDa parasite component

Monoclonal antibodies against Pneumocystis carinii (PC) antigenic epitopes resistant to denaturing procedures were developed by immunization of mice with isolated parasites and a urea extract of infected human lung tissue. Paraffin sections of infected lung tissue were used as antigen in the screening for reactive clones. The target antigen was identified as an 82 kDa parasite specific component in immunoblotting. The antibody showed no cross-reactivity with human lung tissue and various rat tissues and failed to react with a number of parasites and fungi. The antigenic epitope recognized by the anti-82 kDa component was resistant to denaturing procedures involved in fixation and processing of tissues for histology. The antibodies could be used for identification of both cysts and trophozoites in fixed smears of infected lung tissue and bronchoalveolar lavage fluid from infected individuals.

Freeze-fracture studies on Pneumocystis carinii. III. Fine structure of the precyst and the cyst

The ultrastructure of the precyst and cyst of Pneumocystis carinii was investigated by the freeze-fracture method. The most interesting point in this study is the alteration in the number of intramembranous particles (IMPs) of the plasma membrane during the formation of intracystic bodies. The IMP density of delimiting membrane originating from the precyst plasma membrane, which later becomes the plasma membrane of the intracystic body, was low. In contrast, that of the plasma membrane of the intracystic body was as high as that of a typical trophozoite. These results suggest that the protein content of the plasma membrane increases rapidly when the delimiting membranes fuse and intracystic bodies are organized. The plasma membrane of the ruptured cyst, on the other hand, showed lower density and heterogeneous distribution of IMPs. Since all other stages of P. carinii showed homogeneous distribution of IMPs, the denaturation of the plasma membrane after excystation of intracystic bodies is indicated.

Production of a monoclonal antibody with specificity for the pellicle of Pneumocystis carinii by hybridoma

This study reports the establishment of cloned hybridomas between mouse myeloma cells (P3-X63-Ag8, 6.5.3) and spleen cells from BALB/c mice immunized with lung homogenates of nude mice (BALB/c nu/nu) heavily infected with Pneumocystis carinii. A hybridoma subclone, designated 1E12-8, produced antibodies of an IgG1 subclass. Using indirect immunofluorescent antibody techniques, the monoclonal antibody was found to be directed toward the pellicle antigen of air-dried P. carinii both in trophozoite and cyst forms, and to recognize the P. carinii antigen not only from nude mice but also from rats. The antibody did not cross-react with other components of the infected host lung tissue and showed little cross-reactivity with fungi examined. The monoclonal antibody should be useful in the isolation and identification of corresponding antigenic substances of P. carinii and may provide a useful tool in epidemiology, taxonomy, and diagnosis of this organism.

Pneumocystis infection in macaque monkeys: Macaca fuscata fuscata and Macaca fascicularis

Retrospective examination of lungs from 128 monkey necropsies was attempted for Pneumocystis infection using special strains, including toluidine blue-O and Gomori's methenamine silver nitrate. Four Japanese monkeys (7.7%), Macaca fuscata fuscata, and one crab-eating monkey (7.7%), Macaca fascicularis, were found to have Pneumocystis infection. The organism was found in young and infant animals. At the time of death, one infant and two young monkeys were debilitated and/or emaciated. Pneumocystis infection was considered an important lesion which could have caused reduced respiratory function in two of the Japanese monkeys, but constituted only an incidental finding in the others.