Mp1p homologues as virulence factors in Aspergillus fumigatus

Recently, we showed that Mp1p is an important virulence factor of Talaromyces marneffei, a dimorphic fungus phylogenetically closely related to Aspergillus fumigatus. In this study, we investigated the virulence properties of the four Mp1p homologues (Afmp1p, Afmp2p, Afmp3p, and Afmp4p) in A. fumigatus using a mouse model. All mice died 7 days after challenge with wild-type A. fumigatus QC5096, AFMP1 knockdown mutant, AFMP2 knockdown mutant and AFMP3 knockdown mutant and 28 days after challenge with AFMP4 knockdown mutant (P<.0001). Only 11% of mice died 30 days after challenge with AFMP1-4 knockdown mutant (P<.0001). For mice challenge with AFMP1-4 knockdown mutant, lower abundance of fungal elements was observed in brains, kidneys, and spleens compared to mice challenge with QC5096 at day 4 post-infection. Fungal counts in brains of mice challenge with QC5096 or AFMP4 knockdown mutant were significantly higher than those challenge with AFMP1-4 knockdown mutant (P<.01 and P<.05). Fungal counts in kidneys of mice challenge with QC5096 or AFMP4 knockdown mutant were significantly higher than those challenge with AFMP1-4 knockdown mutant (P<.001 and P<.001) and those of mice challenge with QC5096 were significantly higher than those challenge with AFMP4 knockdown mutant (P<.05). There is no difference among the survival rates of wild-type A. fumigatus, AFMP4 knockdown mutant and AFMP1-4 knockdown mutant, suggesting that Mp1p homologues in A. fumigatus do not mediate its virulence via improving its survival in macrophage as in the case in T. marneffei. Afmp1p, Afmp2p, Afmp3p, and Afmp4p in combination are important virulence factors of A. fumigatus.

Mp1p Is a Virulence Factor in Talaromyces (Penicillium) marneffei

Background

Talaromyces marneffei is an opportunistic dimorphic fungus prevalent in Southeast Asia. We previously demonstrated that Mp1p is an immunogenic surface and secretory mannoprotein of T. marneffei. Since Mp1p is a surface protein that can generate protective immunity, we hypothesized that Mp1p and/or its homologs are virulence factors.

Methodology/Principal Findings

We examined the pathogenic roles of Mp1p and its homologs in a mouse model. All mice died 21 and 30 days after challenge with wild-type T. marneffei PM1 and MP1 complemented mutant respectively. None of the mice died 60 days after challenge with MP1 knockout mutant (P<0.0001). Seventy percent of mice died 60 days after challenge with MP1 knockdown mutant (P<0.0001). All mice died after challenge with MPLP1 to MPLP13 knockdown mutants, suggesting that only Mp1p plays a significant role in virulence. The mean fungal loads of PM1 and MP1 complemented mutant in the liver, lung, kidney and spleen were significantly higher than those of the MP1 knockout mutant. Similarly, the mean load of PM1 in the liver, lung and spleen were significantly higher than that of the MP1 knockdown mutant. Histopathological studies showed an abundance of yeast in the kidney, spleen, liver and lung with more marked hepatic and splenic necrosis in mice challenged with PM1 compared to MP1 knockout and MP1 knockdown mutants. Likewise, a higher abundance of yeast was observed in the liver and spleen of mice challenged with MP1 complemented mutant compared to MP1 knockout mutant. PM1 and MP1 complemented mutant survived significantly better than MP1 knockout mutant in macrophages at 48 hours (P<0.01) post-infection. The mean fungal counts of Pichia pastoris GS115-MP1 in the liver (P<0.001) and spleen (P<0.05) of mice were significantly higher than those of GS115 at 24 hours post-challenge.

Conclusions/Significance

Mp1p is a key virulence factor of T. marneffei. Mp1p mediates virulence by improving the survival of T. marneffei in macrophages.

Talaromyces (Penicillium) marneffei is an opportunistic thermal dimorphic fungus most prevalent in Southeast Asia. Our team has previously shown that Mp1p, a protein encoded by the MP1 gene, is an immunogenic surface and secretory protein of T. marneffei. In this study, we showed that mice challenged with T. marneffei with the MP1 gene died but those challenged with T. marneffei without the MP1 gene did not die. There was also significantly higher fungal load and more necrosis in organs of mice challenged with T. marneffei with the MP1 gene than T. marneffei without the MP1 gene. Furthermore, T. marneffei with the MP1 gene survived better in macrophages than T. marneffei without the MP1 gene and Pichia pastoris with the MP1 gene survived in mice better than P. pastoris without the MP1 gene. Our data support that Mp1p is a key virulence factor of T. marneffei and Mp1p mediates virulence by improving the survival of T. marneffei in macrophages.

MP1 homologue-based multilocus sequence system for typing the pathogenic fungus Penicillium marneffei: a novel approach using lineage-specific genes

A highly reproducible and discriminative typing system is essential for better understanding of the epidemiology of Penicillium marneffei, the most important thermal dimorphic fungus causing respiratory, skin, and systemic mycosis in Southeast Asia. The sequences of 11 housekeeping genes were identical among 10 strains of P. marneffei, but those of MP1 and its 13 homologues, a novel superfamily of mannoproteins in the subdivision Pezizomycotina of Ascomycetes, mostly species of Penicillium and Aspergillus, showed significant variations. Therefore, a multilocus sequence typing (MLST) system for P. marneffei was constructed using MP1 (549 bp) and the four of its homologues (MPLP4 [337 bp], MPLP7 [347 bp], MPLP10 [546 bp], and MPLP13 [422 bp]) that showed the greatest variations. Among the 2,201 bp of the five loci, 183 polymorphic sites were observed in 44 strains of P. marneffei. The median number of alleles at each locus was five (range, 5 [MPLP4, MPLP7, and MPLP13] to 15 [MPLP10]). Four of the five genes had nonsynonymous substitution/synonymous substitution (d(n)/d(s)) ratios of >1. A total of 35 different sequence types (STs) were assigned to the 44 P. marneffei isolates, with 28 of the 35 STs identified only once. The discriminatory power was 0.9884. MP1 and its homologues were better than housekeeping genes for MLST in P. marneffei. Due to their more rapid evolutionary rates, lineage-specific genes may be better candidates than housekeeping genes for sequence-based typing, especially in microbes that evolve slowly or have evolved recently.

A novel approach for screening immunogenic proteins inPenicillium marneffeiusing the ΔAFMP1ΔAFMP2deletion mutant ofAspergillus fumigatus

Using serum from guinea-pigs immunized with a DeltaAFMP1DeltaAFMP2 deletion mutant of Aspergillus fumigatus to screen a cDNA library of A. fumigatus, we cloned a novel immunogenic 57-kDa protein in A. fumigatus. We also cloned its 55-kDa homologue in Penicillium marneffei, which was possibly related to amino acid biosynthesis and metabolism, with homologues present only in the subphylum Pezizomycotina of Ascomycota. The recombinant 55-kDa protein of P. marneffei reacted strongly with guinea-pig serum immunized with P. marneffei and with the sera of patients with P. marneffei infection. A similar approach could be applied to immunogenic protein screening in other microorganisms for serological diagnosis, epidemiological studies and the study of vaccines.

Genomic and experimental evidence for a potential sexual cycle in the pathogenic thermal dimorphic fungus Penicillium marneffei

All meiotic genes (except HOP1) and genes encoding putative pheromone processing enzymes, pheromone receptors and pheromone response pathways proteins in Aspergillus fumigatus and Aspergillus nidulans and a putative MAT-1 alpha box mating-type gene were present in the Penicillium marneffei genome. A putative MAT-2 high-mobility group mating-type gene was amplified from a MAT-1 alpha box mating-type gene-negative P. marneffei strain. Among 37 P. marneffei patient strains, MAT-1 alpha box and MAT-2 high-mobility group mating-type genes were present in 23 and 14 isolates, respectively. We speculate that P. marneffei can potentially be a heterothallic fungus that does not switch mating type.

AFMP2 encodes a novel immunogenic protein of the antigenic mannoprotein superfamily in Aspergillus fumigatus

We cloned the Aspergillus fumigatus mannoprotein 2 (AFMP2) gene, which encodes a novel immunogenic protein (Afmp2p) of the antigenic mannoprotein superfamily, in A. fumigatus. Sequence analysis revealed that Afmp2p has 510 amino acid residues, with a predicted molecular mass of 51.5 kDa. Afmp2p has a putative N-terminal signal peptide, a putative C-terminal glycosylphosphatidylinositol membrane attachment signal sequence, and an upstream GAA cleavage site commonly used for cytoplasmic membrane attachment and implicated in fungal cell wall assembly. Upstream of the GAA cleavage site, Afmp2p contains a 302-amino-acid serine- and threonine-rich region as a site for potential O-glycosylation. Within this serine- and threonine-rich region, 13 repeats of ETSTPCE(T)(n) were observed. Western blot analysis of Afmp2p in A. fumigatus fungal cell lysate and culture supernatant and immunogold staining and electron microscopy showed that Afmp2p is predominantly secreted into the culture supernatant, whereas only minimal amounts can be detected in the cell lysate and cell wall. Finally, it was observed that patients with aspergilloma and invasive aspergillosis due to A. fumigatus develop a specific antibody response against recombinant Afmp2p. The abundance of Afmp2p in secreted form, its minimal cross-reactivity with Afmp1p, and the presence of an antibody response against Afmp2p in patients with A. fumigatus infections suggest that Afmp2p is a good candidate for complementing Afmp1p in serodiagnosis of A. fumigatus infections.

Association of presence of Aspergillus antibodies with hemoptysis in patients with old tuberculosis or bronchiectasis but no radiologically visible mycetoma

Old tuberculosis and bronchiectasis are the two most important causes of chronic structural changes of lungs in our locality. In the absence of radiologically visible mycetoma, the cause of hemoptysis in these two groups of patients is largely unknown. A 17-month prospective study was carried out to compare the prevalence of Aspergillus fumigatus and Aspergillus flavus antibodies in hemoptysis patients with old tuberculosis or bronchiectasis but no radiologically visible mycetoma (cases, n = 38), hemoptysis patients with other diagnosis (control group 1, n = 29), and patients with old tuberculosis or bronchiectasis but no hemoptysis (control group 2, n = 47) by a recently developed sensitive and specific A. fumigatus and A. flavus antibody assay. There were a significantly larger number of patients with antibody against A. fumigatus or A. flavus among the cases than among the patients in control groups 1 and 2 (P < 0.05 in both comparisons). Molds were not recovered from any of the patients. Among the 10 cases with Aspergillus antibody, eight and two had antibody against A. flavus and A. fumigatus, respectively. We conclude that there was an association between the presence of Aspergillus antibodies and hemoptysis in patients with old tuberculosis or bronchiectasis, suggesting that these patients probably had occult infections caused by the corresponding fungi. Development of serological tests against other Aspergillus species as well as other causes of mycetoma will probably increase the detection of occult mold infections in patients with existing parenchymal lung diseases, and treatment of fungal microinvasion may help to alleviate hemoptysis in these patients with bronchiectasis or old tuberculosis who have Aspergillus antibodies.

AFLMP1 encodes an antigenic cel wall protein in Aspergillus flavus

We have previously reported the cloning and characterization of the MP1 gene in Penicillium marneffei and the AFMP1 gene in Aspergillus fumigatus and their use for serodiagnosis of penicilliosis and aspergilloma and invasive aspergillosis, respectively. In this study, we describe the cloning of the AFLMP1 gene, which encodes the homologous antigenic cell wall protein in Aspergillus flavus, the most common Aspergillus species associated with human disease in our locality and in other Asian countries and the second most common Aspergillus species associated with human disease in Western countries. AFLMP1 codes for a protein, Aflmp1p, of 273 amino acid residues, with a few sequence features that are present in Mp1p and Afmp1p, the homologous antigenic cell wall proteins in P. marneffei and A. fumigatus, respectively, as well as several other cell wall proteins of Saccharomyces cerevisiae and Candida albicans. It contains a serine- and threonine-rich region for O glycosylation, a signal peptide, and a putative glycosylphosphatidylinositol attachment signal sequence. Specific anti-Aflmp1p antibody was generated with recombinant Aflmp1p protein purified from Escherichia coli to allow further characterization of Aflmp1p. Indirect immunofluorescence analysis indicated that Aflmp1p is present on the surface of the hyphae of A. flavus. Finally, it was observed that patients with aspergilloma and invasive aspergillosis due to A. flavus develop a specific antibody response against Aflmp1p. This suggested that the recombinant protein and its antibody may be useful for serodiagnosis in patients with aspergilloma or invasive aspergillosis, and the protein may represent a good cell surface target for host humoral immunity.

Relatively alcohol-resistant mycobacteria are emerging pathogens in patients receiving acupuncture treatment

Acupuncture has been gaining popularity as a form of alternative medicine. In the past, only blood-borne viruses and anecdotal reports of bacterial infections have been associated with acupuncture. We report on four patients with mycobacterial infections complicating acupuncture who were encountered in a 2-year period. All had clinical and/or radiological lesions at acupuncture point- and meridian-specific locations. There was no other history of trauma or other clinical foci of infections, and the chest radiographs were normal. Histological studies of biopsy specimens of all four patients showed changes compatible with chronic inflammation, with granulomatous inflammation present in three patients and acid-fast bacilli present in two. Conventional biochemical tests and whole-cell fatty acid analysis for identification were inconclusive for all four nonpigmented mycobacteria recovered from tissue biopsies. 16S rRNA gene sequencing showed that the strains from two patients were Mycobacterium chelonae and that those from the other two were Mycobacterium nonchromogenicum. Alcohol resistance assay using the quantitative suspension test revealed that all four strains showed prolonged survival in 75% alcohol compared to other skin flora. Mycobacterial infections transmitted by acupuncture are an emerging problem. A high index of suspicion is essential to recognize this clinical syndrome, and strict implementation of proper infection control guidelines for acupuncture is mandatory.