Pneumocystis carinii exhibits a conserved meiotic control pathway

Retracing the evolution of Pneumocystis species, with a focus on the human pathogen Pneumocystis jirovecii

SUMMARYEvery human being is presumed to be infected by the fungus Pneumocystis jirovecii at least once in his or her lifetime. This fungus belongs to a large group of species that appear to exclusively infect mammals, with P. jirovecii being the only one known to cause disease in humans. The mystery of P. jirovecii origin and speciation is just beginning to unravel. Here, we provide a review of the major steps of P. jirovecii evolution. The Pneumocystis genus likely originated from soil or plant-associated organisms during the period of Cretaceous ~165 million years ago and successfully shifted to mammals. The transition coincided with a substantial loss of genes, many of which are related to the synthesis of nutrients that can be scavenged from hosts or cell wall components that could be targeted by the mammalian immune system. Following the transition, the Pneumocystis genus cospeciated with mammals. Each species specialized at infecting its own host. Host specialization is presumably built at least partially upon surface glycoproteins, whose protogene was acquired prior to the genus formation. P. jirovecii appeared at ~65 million years ago, overlapping with the emergence of the first primates. P. jirovecii and its sister species P. macacae, which infects macaques nowadays, may have had overlapping host ranges in the distant past. Clues from molecular clocks suggest that P. jirovecii did not cospeciate with humans. Molecular evidence suggests that Pneumocystis speciation involved chromosomal rearrangements and the mounting of genetic barriers that inhibit gene flow among species.

Pneumocystis Mating-Type Locus and Sexual Cycle during Infection

Pneumocystis species colonize mammalian lungs and cause deadly pneumonia if the immune system of the host weakens. Each species presents a specificity for a single mammalian host species. Pneumocystis jirovecii infects humans and provokes pneumonia, which is among the most frequent invasive fungal infections. The lack of in vitro culture methods for these fungi complicates their study. Recently, high-throughput sequencing technologies followed by comparative genomics have allowed a better understanding of the mechanisms involved in the sexuality of Pneumocystis organisms. The structure of their mating-type locus corresponding to a fusion of two loci, Plus and Minus, and the concomitant expression of the three mating-type genes revealed that their mode of sexual reproduction is primarily homothallism. This mode is favored by microbial pathogens and involves a single self-compatible mating type that can enter into the sexual cycle on its own. Pneumocystis sexuality is obligatory within the host's lungs during pneumonia in adults, primary infection in children, and possibly colonization. This sexuality participates in cell proliferation, airborne transmission to new hosts, and probably antigenic variation, processes that are crucial to ensure the survival of the fungus. Thus, sexuality is central in the Pneumocystis life cycle. The obligate biotrophic parasitism with obligate sexuality of Pneumocystis is unique among fungi pathogenic to humans. Pneumocystis organisms are similar to the plant fungal obligate biotrophs that complete their entire life cycle within their hosts, including sex, and that are also difficult to grow in vitro.

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.

Characterization of N-Acetylglucosamine Biosynthesis in Pneumocystis species. A New Potential Target for Therapy

N-acetylglucosamine (GlcNAc) serves as an essential structural sugar on the cell surface of organisms. For example, GlcNAc is a major component of bacterial peptidoglycan, it is an important building block of fungal cell walls, including a major constituent of chitin and mannoproteins, and it is also required for extracellular matrix generation by animal cells. Herein, we provide evidence for a uridine diphospho (UDP)-GlcNAc pathway in Pneumocystis species. Using an in silico search of the Pneumocystis jirovecii and P. murina (Pm) genomic databases, we determined the presence of at least four proteins implicated in the Saccharomyces cerevisiae UDP-GlcNAc biosynthetic pathway. These genes, termed GFA1, GNA1, AGM1, and UDP-GlcNAc pyrophosphorylase (UAP1), were either confirmed to be present in the Pneumocystis genomes by PCR, or, in the case of Pm uap1 (Pmuap1), functionally confirmed by direct enzymatic activity assay. Expression analysis using quantitative PCR of Pneumocystis pneumonia in mice demonstrated abundant expression of the Pm uap1 transcript. A GlcNAc-binding recombinant protein and a novel GlcNAc-binding immune detection method both verified the presence of GlcNAc in P. carinii (Pc) lysates. Studies of Pc cell wall fractions using high-performance gas chromatography/mass spectrometry documented the presence of GlcNAc glycosyl residues. Pc was shown to synthesize GlcNAc in vitro. The competitive UDP-GlcNAc substrate synthetic inhibitor, nikkomycin Z, suppressed incorporation of GlcNAc by Pc preparations. Finally, treatment of rats with Pneumocystis pneumonia using nikkomycin Z significantly reduced organism burdens. Taken together, these data support an important role for GlcNAc generation in the cell surface of Pneumocystis organisms.

Evidence for a Pneumocystis carinii Flo8-like transcription factor: insights into organism adhesion

Pneumocystis carinii (Pc) adhesion to alveolar epithelial cells is well established and is thought to be a prerequisite for the initiation of Pneumocystis pneumonia. Pc binding events occur in part through the major Pc surface glycoprotein Msg, as well as an integrin-like molecule termed PcInt1. Recent data from the Pc sequencing project also demonstrate DNA sequences homologous to other genes important in Candida spp. binding to mammalian host cells, as well as organism binding to polystyrene surfaces and in biofilm formation. One of these genes, flo8, a transcription factor needed for downstream cAMP/PKA-pathway-mediated activation of the major adhesion/flocculin Flo11 in yeast, was cloned from a Pc cDNA library utilizing a partial sequence available in the Pc genome database. A CHEF blot of Pc genomic DNA yielded a single band providing evidence this gene is present in the organism. BLASTP analysis of the predicted protein demonstrated 41 % homology to the Saccharomyces cerevisiae Flo8. Northern blotting demonstrated greatest expression at pH 6.0-8.0, pH comparable to reported fungal biofilm milieu. Western blot and immunoprecipitation assays of PcFlo8 protein in isolated cyst and tropic life forms confirmed the presence of the cognate protein in these Pc life forms. Heterologous expression of Pcflo8 cDNA in flo8Δ-deficient yeast strains demonstrated that the Pcflo8 was able to restore yeast binding to polystyrene and invasive growth of yeast flo8Δ cells. Furthermore, Pcflo8 promoted yeast binding to HEK293 human epithelial cells, strengthening its functional classification as a Flo8 transcription factor. Taken together, these data suggest that PcFlo8 is expressed by Pc and may exert activity in organism adhesion and biofilm formation.

Comparative genomics suggests primary homothallism of Pneumocystis species

Pneumocystis species are fungal parasites of mammal lungs showing host specificity. Pneumocystis jirovecii colonizes humans and causes severe pneumonia in immunosuppressed individuals. In the absence of in vitro cultures, the life cycle of these fungi remains poorly known. Sexual reproduction probably occurs, but the system of this process and the mating type (MAT) genes involved are not characterized. In the present study, we used comparative genomics to investigate the issue in P. jirovecii and Pneumocystis carinii, the species infecting rats, as well as in their relative Taphrina deformans. We searched sex-related genes using 103 sequences from the relative Schizosaccharomyces pombe as queries. Genes homologous to several sex-related role categories were identified in all species investigated, further supporting sexuality in these organisms. Extensive in silico searches identified only three putative MAT genes in each species investigated (matMc, matMi, and matPi). In P. jirovecii, these genes clustered on the same contig, proving their contiguity in the genome. This organization seems compatible neither with heterothallism, because two different MAT loci on separate DNA molecules would have been detected, nor with secondary homothallism, because the latter involves generally more MAT genes. Consistently, we did not detect cis-acting sequences for mating type switching in secondary homothallism, and PCR revealed identical MAT genes in P. jirovecii isolates from six patients. A strong synteny of the genomic region surrounding the putative MAT genes exists between the two Pneumocystis species. Our results suggest the hypothesis that primary homothallism is the system of reproduction of Pneumocystis species and T. deformans.

Importance   Sexual reproduction among fungi can involve a single partner (homothallism) or two compatible partners (heterothallism). We investigated the issue in three pathogenic fungal relatives: Pneumocystis jirovecii, which causes severe pneumonia in immunocompromised humans; Pneumocystis carinii, which infects rats; and the plant pathogen Taphrina deformans. The nature, the number, and the organization within the genome of the genes involved in sexual reproduction were determined. The three species appeared to harbor a single genomic region gathering only three genes involved in sexual differentiation, an organization which is compatible with sexual reproduction involving a single partner. These findings illuminate the strategy adopted by fungal pathogens to infect their hosts.

Sexual reproduction among fungi can involve a single partner (homothallism) or two compatible partners (heterothallism). We investigated the issue in three pathogenic fungal relatives: Pneumocystis jirovecii, which causes severe pneumonia in immunocompromised humans; Pneumocystis carinii, which infects rats; and the plant pathogen Taphrina deformans. The nature, the number, and the organization within the genome of the genes involved in sexual reproduction were determined. The three species appeared to harbor a single genomic region gathering only three genes involved in sexual differentiation, an organization which is compatible with sexual reproduction involving a single partner. These findings illuminate the strategy adopted by fungal pathogens to infect their hosts.

Pneumocystis

Since its initial misidentification as a trypanosome some 100 years ago, Pneumocystis has remained recalcitrant to study. Although we have learned much, we still do not have definitive answers to such basic questions as, where is the reservoir of infection, how does Pneumocystis reproduce, what is the mechanism of infection, and are there true species of Pneumocystis? The goal of this review is to provide the reader the most up to date information available about the biology of Pneumocystis and the disease it produces.

The Pneumocystis Ace2 transcription factor regulates cell wall-remodeling genes and organism virulence

Pneumocystis carinii (Pc) β-glucans are major components of the organism cell wall; yet, the regulation of Pc cell wall genesis and remodeling is not well understood. Ace2 transcription factors, which are present in many fungi, regulate glucanases and other enzymes needed for cell wall remodeling. The cloning and heterologous expression of PcAce2 in ace2Δ Saccharomyces cerevisiae demonstrated that PcAce2 can restore the defective glucanase and endochitinase gene expression of the mutant as well as regulate cell wall β-glucan biosynthetic genes. Furthermore, when a reconstructed yeast system was used, PcAce2 activated the transcription of the Pneumocystis gsc1 β-glucan synthetase, confirming the activity of a Pc transcription factor on a native Pneumocystis promoter and gene for the first time. We further observed that Pneumocystis binding to host extracellular matrix proteins and lung epithelial cells induced the phosphorylation (activation) of the PcAce2 transcription factor. Finally, we present a novel method that confirms the role of PcAce2 in modulating organism virulence using ace2Δ Candida glabrata infection in neutropenic mice. Together, these results indicate that the adherence of Pc to lung matrix proteins and epithelial cells leads to the activation of the Ace2 transcription factor, which regulates cell wall degradation and biosynthesis genes that are required for cell wall remodeling.

Substrate analysis of the Pneumocystis carinii protein kinases PcCbk1 and PcSte20 using yeast proteome microarrays provides a novel method for Pneumocystis signalling biology

Pneumocystis carinii (Pc) undergoes morphological transitions between cysts and trophic forms. We have previously described two Pc serine/threonine kinases, termed PcCbk1 and PcSte20, with PcSte20 belonging to a family of kinases involved in yeast mating, while PcCbk1 is a member of a group of protein kinases involved in regulation of cell cycle, shape, and proliferation. As Pc remains genetically intractable, knowledge on specific substrates phosphorylated by these kinases remains limited. Utilizing the phylogenetic relatedness of Pc to Saccharomyces cerevisiae, we interrogated a yeast proteome microarray containing >4000 purified protein based peptides, leading to the identification of 18 potential PcCbk1 and 15 PcSte20 substrates (Z-score > 3.0). A number of these potential protein substrates are involved in bud site selection, polarized growth, and response to mating α factor and pseudohyphal and invasive growth. Full-length open reading frames suggested by the PcCbk1 and PcSte20 protoarrays were amplified and expressed. These five proteins were used as substrates for PcCbk1 or PcSte20, with each being highly phosphorylated by the respective kinase. Finally, to demonstrate the utility of this method to identify novel PcCbk1 and PcSte20 substrates, we analysed DNA sequence data from the partially complete Pc genome database and detected partial sequence information of potential PcCbk1 kinase substrates PcPxl1 and PcInt1. We additionally identified the potential PcSte20 kinase substrate PcBdf2. Full-length Pc substrates were cloned and expressed in yeast, and shown to be phosphorylated by the respective Pc kinases. In conclusion, the yeast protein microarray represents a novel crossover technique for identifying unique potential Pc kinase substrates.

Cutting edge: critical role of intracellular osteopontin in antifungal innate immune responses

We found that absence of osteopontin (OPN) in immunocompromised Rag2(-/-) mice, which lack T and B cells, made the mice extremely susceptible to an opportunistic fungus Pneumocystis, although immunocompetent OPN-deficient mice could clear Pneumocystis as well as wild-type mice. OPN has been studied as an extracellular protein, and the role of an intracellular isoform of OPN (iOPN) is still largely unknown. In this study, we elucidated the mechanism by which iOPN was involved in antifungal innate immunity. First, iOPN was essential for cluster formation of fungal receptors that detect Pneumocystis, including dectin-1, TLR2, and mannose receptor. Second, iOPN played a role as an adaptor molecule in TLR2 and dectin-1 signaling pathways and mediated ERK activation and cytokine production by zymosan, which simultaneously activates TLR2 and dectin-1 pathways. Third, iOPN enhanced phagocytosis and clearance of Pneumocystis. Our study suggests the critical involvement of iOPN in antifungal innate immunity.

Pneumocystis: from a doubtful unique entity to a group of highly diversified fungal species

At the end of the 20th century the unique taxonomically enigmatic entity called Pneumocystis carinii was identified as a heterogeneous group of microscopic Fungi, constituted of multiple stenoxenic biological entities largely spread across ecosystems, closely adapted to, and coevolving in parallel with, mammal species. The discoveries and reasoning that led to the current conceptions about the taxonomy of Pneumocystis at the species level are examined here. The present review also focuses on the biological, morphological and phylogenetical features of Pneumocystis jirovecii, Pneumocystis oryctolagi, Pneumocystis murina, P. carinii and Pneumocystis wakefieldiae, the five Pneumocystis species described until now, mainly on the basis of the phylogenetic species concept. Interestingly, Pneumocystis organisms exhibit a successful adaptation enabling them to dwell and replicate in the lungs of both immunocompromised and healthy mammals, which can act as infection reservoirs. The role of healthy carriers in aerial disease transmission is nowadays recognized as a major contribution to Pneumocystis circulation, and Pneumocystis infection of nonimmunosuppressed hosts has emerged as a public health issue. More studies need to be undertaken both on the clinical consequences of the presence of Pneumocystis in healthy carriers and on the intricate Pneumocystis life cycle to better define its epidemiology, to adapt existing therapies to each clinical context and to discover new drug targets.

Characterization of the meiosis-specific recombinase Dmc1 of pneumocystis

The life cycle of Pneumocystis, which causes life-threatening pneumonia in immunosuppressed patients, remains poorly defined. In the present study, we have identified and characterized an orthologue of dmc1, a gene specific for meiotic recombination in yeast, in 3 species of Pneumocystis. dmc1 is a single-copy gene that is transcribed as ∼1.2-kb messenger RNA, which encodes a protein of 336-337 amino acids. Pneumocystis Dmc1 was 61%-70% identical to those from yeast. Confocal microscopy results indicated that the expression of Dmc1 is primarily confined to the cyst form of Pneumocystis. By sequence analysis of 2 single-copy regions of the human Pneumocystis jirovecii genome, we can infer multiple recombination events, which are consistent with meiotic recombination in this primarily haploid organism. Taken together, these studies support the occurrence of a sexual phase in the life cycle of Pneumocystis.

Update on the diagnosis and treatment of Pneumocystis pneumonia

Pneumocystis is an opportunistic fungal pathogen that causes an often-lethal pneumonia in immunocompromised hosts. Although the organism was discovered in the early 1900s, the first cases of Pneumocystis pneumonia in humans were initially recognized in Central Europe after the Second World War in premature and malnourished infants. This unusual lung infection was known as plasma cellular interstitial pneumonitis of the newborn, and was characterized by severe respiratory distress and cyanosis with little or no fever and no pathognomic physical signs. At that time, only anecdotal cases were reported in adults and usually these patients had a baseline malignancy that led to a malnourished state. In the 1960-1970s additional cases were described in adults and children with hematological malignancies, but Pneumocystis pneumonia was still considered a rare disease. However, in the 1980s, with the onset of the HIV epidemic, Pneumocystis prevalence increased dramatically and became widely recognized as an opportunistic infection that caused potentially life-treating pneumonia in patients with impaired immunity. During this time period, prophylaxis against this organism was more generally instituted in high-risk patients. In the 1990s, with widespread use of prophylaxis and the initiation of highly active antiretroviral therapy (HAART) in the treatment of HIV-infected patients, the number of cases in this specific population decreased. However, Pneumocystis pneumonia still remains an important cause of severe pneumonia in patients with HIV infection and is still considered a principal AIDS-defining illness. Despite the decreased number of cases among HIV-infected patients over the past decade, Pneumocystis pneumonia continues to be a serious problem in immunodeficient patients with other immunosuppressive conditions. This is mostly due to increased use of immunosuppressive medications to treat patients with autoimmune diseases, following bone marrow and solid organ transplantation, and in patients with hematological and solid malignancies. Patients with hematologic disorders and solid organ and hematopoietic stem cell transplantation are currently the most vulnerable groups at risk for developing this infection. However, any patient with an impaired immunity, such as those receiving moderate doses of oral steroids for greater than 4 weeks or those receiving other immunosuppressive medications are at also at significant risk.

Pneumocystis carinii expresses an active Rtt109 histone acetyltransferase

Species in the genus Pneumocystis can cause severe pneumonia in immune-compromised hosts. The identification of specific targets present in Pneumocystis species, but lacking in mammalian hosts, is paramount to developing new means to treat this infection. One such potential protein is Rtt109, which is a type of histone acetyltransferase (HAT) required for DNA replication in fungi, but not found in mammals. Sequence orthologues of Rtt109 are present in other fungi, but are absent in mammals, making it a potential pan-specific target against medically relevant fungi. Accordingly, we sought to identify the presence of an Rtt109 in P. carinii. A Pneumocystis carinii (Pc) Rtt109 165-bp partial sequence was initially identified from the incomplete P. carinii genome database. Subsequently, a full-length, 1,128-bp cDNA with homology to Saccharomyces cerevisiae Rtt109 (39% Basic Local Alignment Search Tool (BLASTP)) was cloned and characterized. Sequence analysis of PcRtt109 indicated that the P. carinii molecule contains the putative catalytic aspartate present in yeast. We further demonstrated that the PcRtt109 expressed in rtt109Δ S. cerevisiae cells restored H3-K56 acetylation and the sensitivity toward DNA-damaging agents of rtt109Δ mutant cells. Purified PcRtt109 had the ability to acetylate lysine-56 of histone H3, similar to the ability of Schizosaccharomyces pombe Rtt109 protein. The site-directed mutagenesis of PcRtt109 D84A, a potential regulatory site in the Rtt109 HAT family, abolished H3 acetylation, whereas a DD218/219AA mutation that compromised the activity of ScRtt109 had little effect, demonstrating similarities and differences in Pneumocystis PcRtt109 compared with yeast Saccharomyces cerevisiae Rtt109. These results indicate that P. carinii contains an Rtt109 HAT molecule, and represent the complete identification and characterization of a HAT molecule from this important opportunistic fungal pathogen.

Characterization of PCEng2, a {beta}-1,3-endoglucanase homolog in Pneumocystis carinii with activity in cell wall regulation

Pneumocystis jirovecii pneumonia is an opportunistic fungal infection that causes severe respiratory impairment in immunocompromised patients. The viability of Pneumocystis organisms is dependent on the cyst cell wall, a structural feature that is regulated by essential cell wall-associated enzymes. The formation of the glucan-rich cystic wall has been previously characterized, but glucan degradation in the organism-specifically, degradation during trophic excystment-is not yet fully understood. Most studies of basic Pneumocystis biology have been conducted in Pneumocystis carinii or Pneumocystis murina, the varieties of this genus that infect rats and mice, respectively. Furthermore, all known treatments for P. jirovecii were initially discovered through studies of P. carinii. Accordingly, in this study, we have identified a P. carinii beta-1,3-endoglucanase gene (PCEng2) that is demonstrated to play a significant role in cell wall regulation. The cDNA sequence contained a 2.2-kb open reading frame with conserved amino acid domains homologous to similar fungal glycosyl hydrolases (GH family 81). The gene transcript showed up-regulation in cystic isolates, and the expressed protein was detected within both cyst and trophic forms. Complementation assays in Eng2-deleted Saccharomyces cerevisiae strains showed restoration of the cell wall separation defect during proliferation, demonstrating the importance of PCEng2 protein. during fungal growth. These findings suggest that regulation of cyst cell wall beta-glucans is a fundamental process during completion of the Pneumocystis life cycle.

Characterization of a novel ADAM protease expressed by Pneumocystis carinii

Pneumocystis species are opportunistic fungal pathogens that cause severe pneumonia in immunocompromised hosts. Recent evidence has suggested that unidentified proteases are involved in Pneumocystis life cycle regulation. Proteolytically active ADAM (named for "a disintegrin and metalloprotease") family molecules have been identified in some fungal organisms, such as Aspergillus fumigatus and Schizosaccharomyces pombe, and some have been shown to participate in life cycle regulation. Accordingly, we sought to characterize ADAM-like molecules in the fungal opportunistic pathogen, Pneumocystis carinii (PcADAM). After an in silico search of the P. carinii genomic sequencing project identified a 329-bp partial sequence with homology to known ADAM proteins, the full-length PcADAM sequence was obtained by PCR extension cloning, yielding a final coding sequence of 1,650 bp. Sequence analysis detected the presence of a typical ADAM catalytic active site (HEXXHXXGXXHD). Expression of PcADAM over the Pneumocystis life cycle was analyzed by Northern blot. Southern and contour-clamped homogenous electronic field blot analysis demonstrated its presence in the P. carinii genome. Expression of PcADAM was observed to be increased in Pneumocystis cysts compared to trophic forms. The full-length gene was subsequently cloned and heterologously expressed in Saccharomyces cerevisiae. Purified PcADAMp protein was proteolytically active in casein zymography, requiring divalent zinc. Furthermore, native PcADAMp extracted directly from freshly isolated Pneumocystis organisms also exhibited protease activity. This is the first report of protease activity attributable to a specific, characterized protein in the clinically important opportunistic fungal pathogen Pneumocystis.

Serum markers in interstitial pneumonia with and without Pneumocystis jirovecii colonization: a prospective study

Background

In patients with chronic respiratory disease, Pneumocystis jirovecii (P. jirovecii) colonization is observed, and may influence disease progression and systemic inflammation. Pneumocystis pneumonia causes interstitial changes, so making a diagnosis of PCP in patients who have interstitial pneumonia (IP) with P. jirovecii colonization is sometimes difficult based on radiography.

Methods

This study investigated the prevalence of P. jirovecii colonization in IP patients and assessed pulmonary injury due to P. jirovecii colonization by measurement of serum markers (KL-6, SP-A, SP-D, and (1→3) β-D-glucan (β-D-glucan)) and the peripheral lymphocyte counts, prospectively. A total of 75 patients with idiopathic pulmonary fibrosis (n = 29), collagen vascular-related interstitial pneumonia (n = 19), chronic bronchitis or pneumonia (n = 20), and Pneumocystis pneumonia (n = 7) were enrolled in this prospective study. P. jirovecii DNA was detected in sputum samples, while serum markers and the lymphocyte count were measured in the peripheral blood.

Results

IP patients (idiopathic pulmonary fibrosis and collagen vascular-related IP) who received oral corticosteroids had a high prevalence of P. jirovecii colonization (23.3%). In IP patients, oral corticosteroid therapy was a significant risk factor for P. jirovecii colonization (P < 0.05). Serum markers did not show differences between IP patients with and without P. jirovecii colonization. The β-D-glucan level and lymphocyte count differed between patients with Pneumocystis pneumonia or P. jirovecii colonization.

Conclusion

Serum levels of KL-6, SP-A, SP-D, and β-D-glucan were not useful for detecting P. jirovecii colonization in IP patients. However, the serum β-D-glucan level and lymphocyte count were useful for distinguishing P. jirovecii colonization from pneumocystis pneumonia in IP patients.

The Pneumocystis meiotic PCRan1p kinase exhibits unique temperature-regulated activity

Pneumocystis organisms are opportunistic fungal pathogens that cause significant pneumonia in immune-compromised hosts. Recent evidence has suggested that Pneumocystis carinii exists as separate mating types, and expresses and regulates proteins that govern meiosis and progression of the life cycle. This study was undertaken to investigate the activity of three life cycle-regulatory proteins in Pneumocystis, including two proteins essential in mating signaling, and a putative meiotic regulator, to determine the conditions under which they are most active. This study used V5/HIS-tagged PCRan1p, PCSte20p, and PCCbk1, purified from Saccharomyces cerevisiae strain, INVSC, as well as an in vitro Escherichia coli protein expression system to determine the optimal expression conditions of each protein in the presence of varying pH, temperature, and metal ions. These studies demonstrate an atypical enzymatic activity in PCRan1p, whereby the kinase was most active in the environmental conditions between 10 and 25 degrees C, compared with a dramatic reduction in activity above 30 degrees C, temperatures typically found within mammalian hosts. Circular dichroism and fluorescence spectroscopy suggest that PCRan1p becomes partially unfolded at 25 degrees C, leading to its most active conformation, whereas continued unfolding as temperature increases results in strongly suppressed activity. These studies suggest that, in vivo, while under conditions within the mammalian lung (typically 37 degrees C), PCRan1p kinase activity is largely suppressed, allowing better conditions for the activation of meiosis, whereas in ex vivo environments, PCRan1p kinase activity increases to arrest progression of the life cycle until conditions become more favorable.