Cross-reacting IgE and IgG antibodies to Pityrosporum ovale mannan and other yeasts in atopic dermatitis

Malassezia restricta: An Underdiagnosed Causative Agent of Blood Culture-Negative Infective Endocarditis

BACKGROUND

Infective endocarditis (IE) is a severe disease requiring microbial identification to successfully adapt its treatment. Currently, identification of its etiological microorganism remains unresolved in 5.2% of cases. We aimed to improve IE diagnosis using an ultra-sensitive molecular technique on cardiac samples in microbiologically nondocumented (culture and conventional polymerase chain reaction [PCR]) IE (NDIE) cases.

METHODS

Cardiac samples explanted in a tertiary hospital in Lyon, France, from patients with definite IE over a 5-year period were retrospectively analyzed. NDIE was defined as Duke definite-IE associated with negative explorations including cardiac samples culture, bacterial amplification, and serologies. Ultrasensitive molecular diagnosis was achieved using the Universal Microbe Detection kit (Molzym®). Fungal identification was confirmed using 26S-rDNA and internal transcribed spacer amplifications. Fungal infection was confirmed using Grocott-Gromori staining, auto-immunohistochemistry on cardiac samples, and mannan serologies.

RESULTS

Among 88 included patients, microbial DNA was detected in all 16 NDIE cases. Bacterial taxa typical of IE etiologies were detected in 13/16 cases and Malassezia restricta in the 3 other cases. In these 3 cases, histological examination confirmed the presence of fungi pathognomonic of Malassezia that reacted with patient sera in an auto-immunohistochemistry assay and cross-reacted with Candida albicans in an indirect immunofluorescent assay.

CONCLUSIONS

M. restricta appears to be an underestimated causative agent of NDIE. Importantly, serological cross-reaction of M. restricta with C. albicans may lead to its misdiagnosis. This is of major concern since M. restricta is intrinsically resistant to echinocandins; the reference treatment for Candida-fungal IE.

Taxonomy of Allergenic Fungi

The Kingdom Fungi contains diverse eukaryotic organisms including yeasts, molds, mushrooms, bracket fungi, plant rusts, smuts, and puffballs. Fungi have a complex metabolism that differs from animals and plants. They secrete enzymes into their surroundings and absorb the breakdown products of enzyme action. Some of these enzymes are well-known allergens. The phylogenetic relationships among fungi were unclear until recently because classification was based on the sexual state morphology. Fungi lacking an obvious sexual stage were assigned to the artificial, now-obsolete category, "Deuteromycetes" or "Fungi Imperfecti." During the last 20 years, DNA sequencing has resolved 8 fungal phyla, 3 of which contain most genera associated with important aeroallergens: Zygomycota, Ascomycota, and Basidiomycota. Advances in fungal classification have required name changes for some familiar taxa. Because of regulatory constraints, many fungal allergen extracts retain obsolete names. A major benefit from this reorganization is that specific immunoglobulin E (IgE) levels in individuals sensitized to fungi appear to closely match fungal phylogenetic relationships. This close relationship between molecular fungal systematics and IgE sensitization provides an opportunity to systematically look at cross-reactivity and permits representatives from each taxon to serve as a proxy for IgE to the group.

Sequence diversity of the intergenic spacer region of the rRNA gene of Cryptococcus albidus isolated from the skin of patients with atopic dermatitis and healthy individuals

The yeast species Cryptococcus albidus var. albidus was found to more often colonize the skin surface of patients with atopic dermatitis (77.0%, 47/61) than that of  healthy subjects (37.5%, 15/40). The intergenic spacer 1 region of the rRNA gene of this species consists of four sequence types: I, II, III and IV. Types I and II were predominant among healthy subjects and atopic dermatitis patients, respectively.

Cutaneous yeast microflora in patients with atopic dermatitis

The skin of persons with atopic dermatitis (AD) is very susceptible to cutaneous infection, and some yeast species may also aggravate AD. The total yeast population of an AD patient’s skin and its relation with individual age and body part remains poorly characterized. The aim of this study was to clarify the differences in cutaneous yeast flora by age and body parts of AD patients.

By swabbing affected body parts (hands, legs, face, neck or trunk), 241 samples were collected from patients with AD (132 children and 109 adults), and as controls, 40 samples were taken from healthy individuals (20 children, 20 adults).

In all, 89 (36.9%) of samples were positive; the yeast isolated belonged to three genera: Candida (27.4%), Malassezia (6.6%), and Rhodotorula (2.9%). Cutaneous colonization with yeasts was two-fold higher in the adults than in children (P<0.0001). The distribution of the yeast species was dependent on the body part sampled: Malassezia predominated in the face, neck, and trunk regions (P=0.0047); Candida more frequently colonized hands and legs (P=0.0029).

Our study showed that cutaneous yeast flora and distribution of yeast species depends significantly on the age of the AD patient and the body part affected by atopic dermatitis.

The cell wall galactomannan antigen from Malassezia furfur and Malassezia pachydermatis contains β-1,6-linked linear galactofuranosyl residues and its detection has diagnostic potential

Lipophilic yeasts of the genus Malassezia are associated with several skin diseases, such as pityriasis versicolor, Malassezia folliculitis, seborrhoeic dermatitis and atopic dermatitis, and are also increasingly associated with catheter-related fungaemia. The cell wall components of pathogenic micro-organisms behave as an antigen and/or ligand of the innate immune response. Live cells of Malassezia furfur and Malassezia pachydermatis did not react with an anti-α-1,2-mannoside antibody. However, they showed a strong hydrophobicity and reactivity with an anti-β-1,3-glucan antibody compared to those of C. albicans. The cell wall polysaccharides of M. furfur and M. pachydermatis were isolated and their structures analysed by 1H and 13C NMR experiments. Both polysaccharides were shown to be β-1,6-linked linear galactofuranosyl polymers with a small amount of mannan. The presence of galactomannan on cells of Malassezia species has not been described previously. The galactomannan did not react with an anti-Aspergillus fumigatus monoclonal antibody which has specificity for β-1,5-linked galactofuranosyl residues. An anti-M. furfur antibody strongly reacted with the galactomannans of M. furfur and M. pachydermatis, but did not react with the galactomannans of Trichophyton rubrum, A. fumigatus or Fonsecaea pedrosoi. The characteristics of the anti-M. furfur antibody suggest that there is potential for diagnosis of Malassezia infections by antigen detection.

Cross-reactivity among fungal allergens: a clinically relevant phenomenon?

Atopic patients suffering from allergic asthma, allergic rhinitis, or atopic eczema often have detectable levels of serum IgE antibodies to fungi. Although the association between fungal sensitisation and different forms of allergic diseases, including allergic asthma and life-threatening allergic bronchopulmonary aspergillosis, is well established, the clinical relevance of cross-reactivity among different fungal species remains largely unknown. Recent progress in molecular cloning of fungal allergens and the availability of more than 40 completely sequenced fungal genomes facilitates characterisation, cloning, and production of highly pure recombinant allergens, identification of homologous and orthologous allergens widespread among the fungal kingdom, in silico prediction, and experimental in vitro and in vivo verification of cross-reactivity between homologous pan-allergens. These studies indicate that cross-reactivity is an important component of fungal sensitisation.

Immediate hypersensitivity to Malassezia furfur and Candida albicans mannans in vivo and in vitro

BACKGROUND

Elevated and correlative Malassezia furfur (M. furfur) and Candida albicans (C. albicans) mannan-specific IgE have been demonstrated in atopic eczema dermatitis syndrome (AEDS) of the head, neck and shoulder (HNS) region of the skin. The significance of these antibodies in vivo has not been demonstrated.

METHODS

Sixty-five AEDS patients with HNS distribution were included. Serum total IgE (S-IgE) and yeast antigen-specific (Cetavlon-purified mannan and whole extract antigens of M. furfur and C. albicans) IgE were measured and skin prick tests (SPT) were performed with the yeast antigens.

RESULTS

Mannan-specific IgE and SPT were positive in 51 and 48% of patients with M. furfur and in 42 and 22% with C. albicans, respectively. Whole extract-specific IgE and SPT were positive in 85 and 95% of patients with M. furfur and in 91 and 57% with C. albicans, respectively. The highest correlation between specific IgE and SPT was seen with M. furfur mannan (r = 0.60; P < 0.0001). Both M. furfur mannan-specific IgE (r = 0.76; P < 0.0001) and SPT (r = 0.44; P = 0.0005) correlated with S-IgE.

CONCLUSIONS

Mannan-induced immediate hypersensitivity in vivo was demonstrated in SPT. The significant correlation between M. furfur mannan-specific IgE and SPT suggests that mannan is an important allergen in yeast hypersensitive AEDS in vivo.

Atopic dermatitis and fungi

Atopic dermatitis (AD) is a chronic, itching, inflammatory skin disease which is associated with asthma and/or hay fever and a familial occurrence of these conditions. Genetic factors are important in the development of AD, but the exact hereditary pathway is still unknown. Dry skin and the weakened barrier function in patients with AD is very important for the patient's reactions to irritants and other external trigger factors including microorganisms. The standard treatments are topical corticosteroids, topical immunomodulating agents, and emollients. If AD cannot be controlled by this type of treatment, systemic immunomodulating agents may be used. UVB, UVA, or psoralen-UVA may also be used for widespread severe lesions. However, some patients do not respond to these standard treatment, and then it is important to consider the role of microorganisms, house dust mites or food. The role of the Malassezia yeasts in AD, especially AD located to the head and neck region, is now documented in several papers. There are also several papers indicating the role of Candida as an aggravating factor in AD. Patients with AD also develop chronic dermatophyte infections more easily, and patients with AD and chronic dermatophyte infections may show improvement in their AD when treated with antifungal drugs.

IgG and IgE immune response against the surface glycoprotein gp200 of Saccharomyces cerevisiae in patients with atopic dermatitis

The heat-stable and soluble glycoprotein gp200 (molecular weight 200 kDa) is part of the cell wall of S. cerevisiae. Recently, an association was shown between IgA and IgG against gp200 and inflammation in Crohn's disease. Gp200 is able to induce a proliferation of human lymphocytes in vitro, together with a natural killer cell associated cytotoxicity. Specific IgE against Saccharomyces cerevisiae (baker's or brewer's yeast) may be detected in approximately 73%, against Candida albicans in 68% of those patients suffering from severe atopic dermatitis. The aim of this study was to elucidate the possible role of an anti-gp200 immune response for the pathogenesis of atopic dermatitis by immunoblot analysis. Anti-gp200 IgE was found in 55% of healthy individuals, in 67% of individuals with atopic predisposition without eczema, in 63% of the patients with mild atopic dermatitis, and in 86% of patients with severe atopic dermatitis, respectively. On the contrary, anti-gp200 IgG could be shown in 55% of healthy individuals, in 89% of individuals with atopic predisposition but without eczema, in 100% of patients with mild atopic dermatitis, and in 79% with severe atopic dermatitis, respectively. No immunoreactivity was found when an extract of Arxula adeninivorans was used as antigen. These results underline the specificity of the immunoblot results with gp200 from Saccharomyces cerevisiae. It can be concluded that occurrence of specific IgE against Saccharomyces cerevisiae cannot be explained by a cross reactivity, e.g., against Candida albicans allergens. Further investigations with the recombinant gp200 will give information on the role of this glycoprotein both in atopic dermatitis and Morbus Crohn.

Immunology of diseases associated with Malassezia species

Malassezia species are members of the human cutaneous commensal flora, in addition to causing a wide range of cutaneous and systemic diseases in suitably predisposed individuals. Studies examining cellular and humoral immune responses specific to Malassezia species in patients with Malassezia-associated diseases and healthy controls have generally been unable to define significant differences in their immune response. The use of varied antigenic preparations and strains from different Malassezia classifications may partly be responsible for this, although these problems can now be overcome by using techniques based on recent work defining some important antigens and also a new taxonomy for the genus. The finding that the genus Malassezia is immunomodulatory is important in understanding its ability to cause disease. Stimulation of the reticuloendothelial system and activation of the complement cascade contrasts with its ability to suppress cytokine release and downregulate phagocytic uptake and killing. The lipid-rich layer around the yeast appears to be pivotal in this alteration of phenotype. Defining the nonspecific immune response to Malassezia species and the way in which the organisms modulate it may well be the key to understanding how Malassezia species can exist as both commensals and pathogens.

N- and O-linked oligosaccharides of allergenic glycoproteins

Cross-linking of cell-bound IgE on mast cells or basophils by polyvalent antigens causes the release of histamine and other mediators of the allergic response which then lead to the development of allergic symptoms. In this event not only peptide epitopes, but also carbohydrates can act as cross-linking elements. Since peptide epitopes of allergens are subject of most published studies, this review is focused on glycosidic epitopes. The current knowledge of the structures and possible epitopes of oligosaccharides linked to allergenic glycoproteins is briefly reviewed, showing that complex plant N-glycans containing alpha1,3 fucose and beta1,2 xylose are most frequently involved in the structures of IgE epitopes. In own studies a prevalence of up to 29% anti-glycan IgE was determined among pollen-allergic patients. The clinical relevance of these carbohydrate specific IgE antibodies is still a matter of controversial discussions.