Penicillium glabrum is a saprophyte fungus part of the Penicillium genus, one of the four most common fungal causes of allergy in humans. P. glabrum is associated with suberosis, an occupational hypersensitivity associated with cork production. It is also a mold commonly found in homes. Although no P. glabrum specific allergen is recognized, two protein components of 12–13.5 kDa and 33 kDa are significant in the pathogenesis of suberosis. 

Worldwide distribution 

A study from the USA found that 8.2% of a cohort comprising of children with asthma were sensitized to Penicillium spp. (5). Elsewhere, sensitization to a Penicillium allergen, Pen Ch, was relatively low amongst patients with atopic dermatitis (6). Another study found that 100% (n=16) of workers with a history of occupational exposure to cork and who had either HP or asthma were sensitized to P. glabrum specific allergens. However, the immunological response reported was a specific IgG response, with no IgE response found (3). In Portugal, it is estimated that 9-19% of cork workers may develop suberosis (7). 

Living environment

Penicillium spp., as xerophilic fungi, are characterized as indoor allergens (6) and are one of the three most common indoor airborne fungi (1). One study has found Penicillium spp. present in 33 % of homes (n=1,233) in the North Eastern United States (5). Furthermore, a survey of homes in Eastern France found that P. glabrum was the second most prevalent Penicillium species (22.9%) isolated (8). 

Main

Exposure and sensitization to P. glabrum allergens are most commonly achieved by inhaling fungal fragments (7). 

Penicillium spp. are considered by the institute of medicine to be causative agents of allergic rhinitis in children and adults, as well as asthma children and occupational asthma in adults (8).

In contrast to other allergenic molds, a study in the USA found that increased prevalence of Penicillium correlated with increased risk of clinically apparent hypersensitivity (incident wheeze and persistent cough) (5). Children who were both sensitized to Penicillium spp. and who lived in a household where Penicillium spp. were detected, even at low levels, were twice as likely to experience a higher asthma severity score than the cohort who were either not sensitized or exposed. This contrasts with data for another fungal genus, Cladosporium, which showed sensitivity and exposure status were not associated with clinical outcomes (5).

HP is a lung disease characterized by lymphocytic – histiocytic inflammation of the alveoli, bronchioles and pulmonary interstitium, mainly through inhalation of organic substances. HP is probably underdiagnosed (9). Suberosis, of which P. glabrum is the primary causative agent (3), is a form of HP associated with repeated exposure to moldy cork dust in workplaces where this material is used in industrial processing. 

Allergenic molecules

Although the WHO-IUIS Allergen Nomenclature Sub-Committee recognizes multiple allergens from Penicillium species, their role in the pathogenesis of Penicillium hypersensitivity is yet to be described. The major Penicillium allergens are proteases (alkaline and vacuolar serine proteases) and are referred to as group 14 and group 18 allergens due to their high sequence homology with the Aspergillus fumigatus allergens Asp f 14 and Asp f 18. Furthermore, there are no approved allergens specific to P. glabrum (1).

One study, which aimed to characterize the P.glabrum allergen, using sera from patients with suberosis or asthma, found two P. glabrum proteins that could be candidate allergens. The components (12–13.5 kDa and 33 kDa) were significantly associated with clinical HP. Although the study did not demonstrate IgE binding of the 33 kDa component, IgE binding has been shown with components of 33 kDa in other Penicillium spp. (3).

Cross-reactivity

Mono-sensitization to P. glabrum is unlikely as the Penicillium specific allergens described are characteristically cross-reactive (1).

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

Last reviewed:March 2022