Western immunoblot analysis of protein antigens of Penicillium marneffei

Antibody screening reveals antigenic proteins involved in Talaromyces marneffei and human interaction

Talaromycosis is a fungal infection that generally affects immunocompromised hosts and is one of the most frequent systemic mycoses in HIV patients, especially in endemic areas such as Southeast Asia. Talaromyces marneffei, the causative agent of talaromycosis, grows as a mold in the environment but adapts to the human body and host niches by transitioning from conidia to yeast-like cells. Knowledge of the human host and T. marneffei interaction has a direct impact on the diagnosis, yet studies are still lacking. The morbidity and mortality rates are high in taloromycosis patients if the diagnosis and treatments are delayed. Immunogenic proteins are excellent candidates for developing detection tools. Previously, we identified antigenic proteins that were recognized by antibodies from talaromycosis sera. Three of these identified proteins have been previously characterized in detail, while the others have not been explored. To expedite the progress of antigen discovery, the complete list of antigenic proteins and their features was fully reported in this study. Functional annotation and Gene Ontology examination revealed that these proteins showed a high association with membrane trafficking. Further bioinformatics analyses were performed to search for antigenic protein characteristics, including functional domains, critical residues, subcellular localization, secretory signals, and epitope peptide sequences. Expression profiling of these antigenic encoding genes was investigated using quantitative real-time PCR. The results demonstrated that most genes were expressed at low levels in the mold form, but were highly upregulated in the pathogenic yeast phase, consistent with the antigenic role of these genes during the human-host interaction. Most transcripts accumulated in the conidia, suggesting a role during phase transition. The collection of all antigen-encoding DNA sequences described here is freely accessible at GenBank, which could be useful for the research community to develop into biomarkers, diagnostic tests, research detection tools, and even vaccines.

An Overlooked and Underrated Endemic Mycosis-Talaromycosis and the Pathogenic Fungus Talaromyces marneffei

Talaromycosis is an invasive mycosis endemic in tropical and subtropical Asia and is caused by the pathogenic fungus Talaromyces marneffei. Approximately 17,300 cases of T. marneffei infection are diagnosed annually, and the reported mortality rate is extremely high (~1/3). Despite the devastating impact of talaromycosis on immunocompromised individuals, particularly HIV-positive persons, and the increase in reported occurrences in HIV-uninfected persons, diagnostic and therapeutic approaches for talaromycosis have received far too little attention worldwide. In 2021, scientists living in countries where talaromycosis is endemic raised a global demand for it to be recognized as a neglected tropical disease. Therefore, T. marneffei and the infectious disease induced by this fungus must be treated with concern. T. marneffei is a thermally dimorphic saprophytic fungus with a complicated mycological growth process that may produce various cell types in its life cycle, including conidia, hyphae, and yeast, all of which are associated with its pathogenicity. However, understanding of the pathogenic mechanism of T. marneffei has been limited until recently. To achieve a holistic view of T. marneffei and talaromycosis, the current knowledge about talaromycosis and research breakthroughs regarding T. marneffei growth biology are discussed in this review, along with the interaction of the fungus with environmental stimuli and the host immune response to fungal infection. Importantly, the future research directions required for understanding this serious infection and its causative pathogenic fungus are also emphasized to identify solutions that will alleviate the suffering of susceptible individuals worldwide.

Diagnostic laboratory immunology for talaromycosis (penicilliosis): review from the bench-top techniques to the point-of-care testing

The pathogenic fungus Talaromyces (formerly Penicillium) marneffei is a thermally dimorphic fungus that can cause disseminated infection in patients with secondary immunodeficiency syndrome, in particular in the setting of advanced HIV infection. The areas of highest incidence are in Southeast Asia, Southern China, and Indian subcontinents. Talaromycosis (formerly penicilliosis) is identified as an AIDS-defining illness, and it has recently been recognized in non-HIV-associated patients with impaired cellular-mediated immunity. Microbiological culture is the gold standard method for the diagnosis of T. marneffei infection and usually requires up to 2-4 weeks for detectable growth to occur, which may result in a delay of appropriate treatment. Immunodiagnosis has become an alternative method for confirming talaromycosis. This article reviews various immunological tests for the diagnosis of talaromycosis, including a proposed novel rapid point-of-care assay using a new T. marneffei yeast phase-specific monoclonal antibody.

Characterization of an MPLP6, a gene coding for a yeast phase specific, antigenic mannoprotein in Penicillium marneffei

A gene encoding an antigenic mannoprotein of Penicillium marneffei, MPLP6, was isolated by an antibody screening approach and characterized. The polypeptide chain containing deduced 220 amino acids has a predicted molecular mass of 24 kDa. It has high similarity to Mp1p, the first mannoprotein antigen isolated from P. marneffei. The polypeptide sequence presents the property of cell wall mannoproteins by containing a putative N-terminal signal peptide and potential O-linked glycosylation sites. However, absence of a GPI-anchored signal sequence suggested that this protein is secreted. The MPLP6 transcript was present specifically in the pathogenic yeast form. The transcript was completely absent in the mold phase and conidia. The fusion protein produced in E. coli was Western immunoblotted with P. marneffei-infected human sera and 95% of the patients' sera were positive in the assay. None of the sera obtained from patients with aspergillosis, tuberculosis, histoplasmosis or cryptococcosis tested positive. These results suggest that Mplp6 can be used as a marker in a serodiagnostic assay.

Penicillium marneffei infection and recent advances in the epidemiology and molecular biology aspects

Penicillium marneffei infection is an important emerging public health problem, especially among patients infected with human immunodeficiency virus in the areas of endemicity in southeast Asia, India, and China. Within these regions, P. marneffei infection is regarded as an AIDS-defining illness, and the severity of the disease depends on the immunological status of the infected individual. Early diagnosis by serologic and molecular assay-based methods have been developed and are proving to be important in diagnosing infection. The occurrence of natural reservoirs and the molecular epidemiology of P. marneffei have been studied; however, the natural history and mode of transmission of the organism remain unclear. Soil exposure, especially during the rainy season, has been suggested to be a critical risk factor. Using a highly discriminatory molecular technique, multilocus microsatellite typing, to characterize this fungus, several isolates from bamboo rats and humans were shown to share identical multilocus genotypes. These data suggest either that transmission of P. marneffei may occur from rodents to humans or that rodents and humans are coinfected from common environmental sources. These putative natural cycles of P. marneffei infection need further investigation. Studies on the fungal genetics of P. marneffei have been focused on the characterization of genetic determinants that may play important roles in asexual development, mycelial-to-yeast phase transition, and the expression of antigenic determinants. Molecular studies have identified several genes involved in germination, hyphal development, conidiogenesis, and yeast cell polarity. A number of functionally important genes, such as the malate synthase- and catalase-peroxidase protein-encoding genes, have been identified as being upregulated in the yeast phase. Future investigations pertaining to the roles of these genes in host-fungus interactions may provide the key knowledge to understanding the pathogenicity of P. marneffei.

Development and evaluation of rapid urinary antigen detection tests for diagnosis of penicilliosis marneffei

Penicilliosis, caused by the dimorphic fungus Penicillium marneffei, is an important opportunistic systemic fungal infection affecting immunocompromised individuals living in areas where penicilliosis is endemic. We have demonstrated previously that a urinary enzyme-linked immunosorbent assay (ELISA) with purified rabbit polyclonal antibody against killed whole-fission-form arthroconidia of P. marneffei was specific and highly sensitive for the diagnosis of penicilliosis. In this study, a dot blot ELISA and a latex agglutination (LA) test were developed with the same polyclonal antibody and compared with the ELISA for the detection of P. marneffei urinary antigen. Urine specimens from 37 patients with culture-proven penicilliosis and 300 controls (52 healthy subjects and 248 hospitalized patients without penicilliosis) were tested. Antigen was detected in urine from all 37 (100%) penicilliosis patients by the LA test, 35 (94.6%) penicilliosis patients by the dot blot ELISA, and 36 (97.3%) penicilliosis patients by the ELISA. False-positive results were found by the three assays for 2 (0.7%), 8 (2.7%), and 6 (2%) of 300 controls, respectively. The overall sensitivities of the diagnostic tests were as follows: dot blot ELISA, 94.6%; ELISA, 97.3%; and LA test, 100% (specificities, 97.3, 98, and 99.3%, respectively). The LA test is simple, robust, rapid, and convenient and should prove to be an important addition to the existing diagnostic tests for penicilliosis.

Rapid identification of Penicillium marneffei by PCR-based detection of specific sequences on the rRNA gene

An emerging pathogenic dimorphic fungus, Penicillium marneffei, is one of the major causes of morbidity in patients with human immunodeficiency virus infection in Southeast Asia. A PCR-hybridization assay has been developed to identify this pathogen. This study describes the use of single and nested PCR methods for the rapid identification of P. marneffei. Two sets of oligonucleotide primers were derived from the sequence of 18S rRNA genes of P. marneffei. The outer primers (RRF1 and RRH1) were fungus specific. The inner primers (Pm1 and Pm2) were specific for P. marneffei and were used in nested or single PCR. The specific fragment of approximately 400-bp was amplified from both mold and yeast forms of 13 P. marneffei human isolates, 12 bamboo rat isolates, and 1 soil isolate, but not from other fungi, bacteria, and human DNA. The amplified products were analyzed by agarose gel electrophoresis followed by ethidium bromide staining. The sensitivities of the single PCR and nested PCR were 1.0 pg/microl and 1.8 fg/microl, respectively. The assay is useful for rapid identification of P. marneffei cultures. Very young culture of P. marneffei (2-day-old filamentous colony, 2 mm in diameter) could be performed by this assay. The species was identified within 7 h (single PCR) or 10 h (nested PCR), compared to 4 to 7 days for confirmation of dimorphism. The application of these PCR methods for early diagnosis of the disease needs to be studied further.

Cutaneous manifestations of Penicillium marneffei infection

From an almost unknown disease 15 years ago, Penicillium marneffei has emerged to become one of the most common opportunistic fungal pathogens among HIV-infected patients in the endemic area of southern China and northern Thailand. The mode of infection is primarily airborne, with the reticuloendothelial system as the main target. Penicilliosis is a fatal disease and systemic antifungals are the mainstay of therapy. Direct and mycological examinations are sufficient to make a diagnosis and to differentiate P. marneffei from other opportunistic fungi, although advances in serodiagnosis may potentially enhance understanding of the pathogenesis and identification of early asymptomatic cases.

Analysis of the enzymatic activity of mycelial and yeast phases of Penicillium marneffei

The cell-associated and extracellular enzymatic activities were examined in a total of 10 Penicillium marneffei isolates. Both mycelia and yeast expressed alkaline phosphatase, acid phosphatase and naphthol-AS-BI-phosphohydrolase activities, whereas a variety of other enzyme activities, including trypsin, chymotrypsin and alpha-fucosidase were absent. There was some inter-isolate variation in both mycelia and yeast in the activities of other enzymes such as esterases and galactosidases. Enzyme activities did not change significantly over the course of culturing in three representative isolates.

Role of superoxide anion in the fungicidal activity of murine peritoneal exudate macrophages against Penicillium marneffei

Penicillium marneffei is an important opportunistic fungal pathogen. The mechanisms of host defense against P. marneffei are not fully understood. In the present study, we, for the first time, investigated the role of superoxide anion (O2-) in the killing of two forms of P. marneffei, yeast cells and conidia, and the role of this killing mediator in the fungicidal activity of IFN-gamma-stimulated murine peritoneal macrophages. P. marneffei yeast cells were susceptible to the killing effect of activated macrophages and chemically generated O2, while conidia were not. These results suggested that O2- played some role in the fungicidal activity of macrophages. However, an oxygen radical scavenger, superoxide dismutase (SOD), did not suppress, but rather enhanced the fungicidal activity of IFN-gamma-stimulated macrophages against P. marneffei yeast cells. This inconsistency was explained by the release of insufficient concentrations of O2- by activated macrophages as compared with the amount of O2- necessary for the killing of yeast cells, which was predicted in a chemical generating system. On the other hand, SOD enhanced the production of nitric oxide (NO) by IFN-gamma-activated macrophages, and their increased fungicidal activity was significantly inhibited by N(G)-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO synthase. Our results suggested that O2- does not function as the killing mediator of macrophages against P. marneffei, but rather plays an important role in the regulation of the NO-mediated killing system by suppressing NO production.

Detection of specific antibodies to an antigenic mannoprotein for diagnosis of Penicillium marneffei penicilliosis

The disseminated and progressive fungal disease Penicillium marneffei penicilliosis is one of the most common infectious diseases in AIDS patients in Southeast Asia. To diagnose systemic penicilliosis, we developed an enzyme-linked immunosorbent assay (ELISA)-based antibody test with Mp1p, a purified recombinant antigenic mannoprotein of P. marneffei. Evaluation of the test with guinea pig sera against P. marneffei and other pathogenic fungi indicated that this assay was specific for P. marneffei. Clinical evaluation revealed that high levels of specific antibody were detected in two immunocompetent penicilliosis patients. Furthermore, approximately 80% (14 of 17) of the documented penicilliosis patients with human immunodeficiency virus tested positive for the specific antibody. No false-positive results were found for serum samples from 90 healthy blood donors, 20 patients with typhoid fever, and 55 patients with tuberculosis, indicating a high specificity of the test. Thus, this ELISA-based test for the detection of anti-Mp1p antibody can be of significant value as a diagnostic for penicilliosis.

Epidemiology and management of penicilliosis in human immunodeficiency virus-infected patients

Penicillium marneffei is a dimorphic fungus that can cause systemic mycosis in humans. It is endemic in Southeast Asia, the Guangxi province of China, Hong Kong, and Taiwan. Prior to the epidemic of human immunodeficiency virus (HIV), penicilliosis was a rare event. The incidence of this fungal infection has increased markedly during the past few years, paralleling the incidence of HIV infection. The patients usually present with fever, anemia, weight loss, skin lesions, generalized lymphadenopathy, and hepatomegaly. The skin lesions are most commonly papules with central necrotic umbilication. The average number of CD4+ T lymphocytes at presentation is 64 cells/mm3. The fungus is usually sensitive to amphotericin B, itraconazole, and ketoconazole. The response to antifungal treatment is good if the treatment is started early. After the initial treatment the patient may need to take an antifungal drug as secondary prophylaxis for life. New tests for the laboratory diagnosis of penicilliosis have been reported. Further studies of these tests, as well as the epidemiology, natural history, and management of this potentially fatal systemic fungal infection are needed.

Identification and purification of specific Penicillium marneffei antigens and their recognition by human immune sera

Disseminated infection with the dimorphic pathogenic fungus Penicillium marneffei is increasingly seen among patients with AIDS in southeast Asian countries. Previous studies have demonstrated the presence of humoral immune responses to this fungus in patient sera; we have confirmed this work using sera from P. marneffei-infected patients (n = 21) to develop Western blots of P. marneffei cytoplasmic yeast antigen (CYA). P. marneffei CYA was then partially purified by liquid isoelectric focusing, and fractions were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Immunoenzyme development of the Western blots with pooled sera from patients with P. marneffei infection and with pooled sera from patients with aspergillosis (n = 20), candidiasis (n = 10), cryptococcosis (n = 9), and histoplasmosis (n = 11) revealed three antigens with relative molecular masses of 61, 54, and 50 kDa. These antigens were specifically recognized by the pooled sera from the P. marneffei-infected patients. The 61- and 54-kDa antigens were subsequently purified to homogeneity by preparative gel electrophoresis, and the 50-kDa antigen was partially purified by the same technique. N-terminal amino acid sequencing revealed that the 61-kDa antigen had a strong homology (87% identity) with the antioxidant enzyme catalase. The three antigens were then subjected to SDS-PAGE and Western blotting and to immunoenzyme development with individual patient sera; sera from 86% of P. marneffei-infected patients recognized the 61-kDa antigen, sera from 71% recognized the 54-kDa antigen, and sera from 48% recognized the 50-kDa antigen. These specifically recognized antigens are the first to be purified from P. marneffei and can be used either singly or in combination to detect antibody responses in a large percentage of individuals infected with P. marneffei.