Diagnosis of filamentous fungi on tissue sections by immunohistochemistry using anti-aspergillus antibody

Review of immunohistochemistry techniques: Applications, current status, and future perspectives

The Hematoxylin and Eosin stain is a cornerstone in histopathology that facilitates the microscopic examination of tissue samples for identifying infections and tumors. However, challenges arise from the similar appearances of diseases and cells, prompting the emergence of Immunohistochemistry (IHC) as an important technique. This review summarizes the principles, procedures, and applications and future perspectives of IHC, a prevalent immunostaining method allowing the detection of specific proteins in tissue sections. The multistep IHC process involves fixation, embedding, sectioning, antigen retrieval, blocking, detection, counterstaining, mounting, and visualization, with interpretation relying on factors such as microanatomic distribution and staining intensity. Common errors in IHC such as non-specific staining, tissue artifacts, inadequately inactivation of endogenous peroxidase activity and cross-reactivity, can substantially affect the accuracy and reliability of results, thereby impacting the interpretation of biological findings. Serving diagnostic, prognostic, predictive, and therapeutic roles in various conditions, including tumors, infectious diseases, neurodegenerative disorders, and muscle diseases, IHC remains pivotal despite its intricate nature. The adoption of digital pathology emerges as a progressive enhancement, addressing limitations and ensuring more accurate analyses in histopathology.

Pathological Diagnosis of Pulmonary Aspergillosis

Pulmonary aspergillosis constitutes an increasingly prevalent and potentially fatal complex of mycotic diseases, caused by different species of Aspergillus. The broad spectrum of pathological manifestations associated with pulmonary aspergillosis necessitates a differentiation of commensalism from saprophytic colonization, hypersensitivity reactions, and true invasive infections, which highlights the importance of histopathology as a gold standard in a diagnostic setting. For the past decades, changes in terminology and contradicting contributions from different diagnostic disciplines have made the classification of pulmonary aspergillosis rather confusing. This review offers a categorization of aspergillosis lesions based on what can be histopathologically identified and distinguished, differentiating between acute invasive infection and forms of subacute, chronic, and allergic diseases and coinfections, and summarizes important manifestations of lesions associated with the different forms of pulmonary aspergillosis.

Comparison Approach for Identifying Missed Invasive Fungal Infections in Formalin-Fixed, Paraffin-Embedded Autopsy Specimens

Invasive fungal infection (IFI) has a high mortality rate in patients who undergo hematopoietic stem cell transplantation, and it is often confirmed by postmortem dissection. When IFI is initially confirmed after an autopsy, the tissue culture and frozen section are challenging to secure, and in many cases, formalin-fixed, paraffin-embedded (FFPE) samples represent the only modality for identifying fungi. Histopathological diagnosis is a useful method in combination with molecular biological methods that can achieve more precise identification with reproducibility. Meanwhile, polymerase chain reaction (PCR) using fungal-specific primers helps identify fungi from FFPE tissues. Autopsy FFPE specimens have a disadvantage regarding the quality of DNA extracted compared with that of specimens obtained via biopsy or surgery. In the case of mucormycosis diagnosed postmortem histologically, we examined currently available molecular biological methods such as PCR, immunohistochemistry (IHC), and in situ hybridization (ISH) to identify fungi. It is reasonable that PCR with some modification is valuable for identifying fungi in autopsy FFPE specimens. However, PCR does not always correctly identify fungi in autopsy FFPE tissues, and other approaches such as ISH or IHC are worth considering for clarifying the broad classification (such as the genus- or species-level classification).

Immunohistochemical diagnosis of human infectious diseases: a review

BACKGROUND

Immunohistochemistry (IHC) using monoclonal and polyclonal antibodies is a useful diagnostic method for detecting pathogen antigens in fixed tissues, complementing the direct diagnosis of infectious diseases by PCR and culture on fresh tissues. It was first implemented in a seminal publication by Albert Coons in 1941.

MAIN BODY

Of 14,198 publications retrieved from the PubMed, Google, Google Scholar and Science Direct databases up to December 2021, 230 were selected for a review of IHC techniques, protocols and results. The methodological evolutions of IHC and its application to the diagnosis of infectious diseases, more specifically lice-borne diseases, sexually transmitted diseases and skin infections, were critically examined. A total of 59 different pathogens have been detected once in 22 different tissues and organs; and yet non-cultured, fastidious and intracellular pathogens accounted for the vast majority of pathogens detected by IHC. Auto-IHC, incorporating patient serum as the primary antibody, applied to diseased heart valves surgically collected from blood culture-negative endocarditis patients, detected unidentified Gram-positive cocci and microorganisms which were subsequently identified as Coxiella burnetii, Bartonella quintana, Bartonella henselae and Tropheryma whipplei. The application of IHC to ancient tissues dated between the ends of the Ptolemaic period to over 70 years ago, have also contributed to paleomicrobiology diagnoses.

CONCLUSION

IHC plays an important role in diagnostic of infectious diseases in tissue samples. Paleo-auto-IHC derived from auto-IHC, is under development for detecting non-identified pathogens from ancient specimens.

Deep convolutional neural network: a novel approach for the detection of Aspergillus fungi via stereomicroscopy

Fungi of the genus Aspergillus are ubiquitously distributed in nature, and some cause invasive aspergillosis (IA) infections in immunosuppressed individuals and contamination in agricultural products. Because microscopic observation and molecular detection of Aspergillus species represent the most operator-dependent and time-intensive activities, automated and cost-effective approaches are needed. To address this challenge, a deep convolutional neural network (CNN) was used to investigate the ability to classify various Aspergillus species. Using a dissecting microscopy (DM)/stereomicroscopy platform, colonies on plates were scanned with a 35× objective, generating images of sufficient resolution for classification. A total of 8,995 original colony images from seven Aspergillus species cultured in enrichment medium were gathered and autocut to generate 17,142 image crops as training and test datasets containing the typical representative morphology of conidiophores or colonies of each strain. Encouragingly, the Xception model exhibited a classification accuracy of 99.8% on the training image set. After training, our CNN model achieved a classification accuracy of 99.7% on the test image set. Based on the Xception performance during training and testing, this classification algorithm was further applied to recognize and validate a new set of raw images of these strains, showing a detection accuracy of 98.2%. Thus, our study demonstrated a novel concept for an artificial-intelligence-based and cost-effective detection methodology for Aspergillus organisms, which also has the potential to improve the public's understanding of the fungal kingdom.

Molecular Techniques for Genus and Species Determination of Fungi From Fresh and Paraffin-Embedded Formalin-Fixed Tissue in the Revised EORTC/MSGERC Definitions of Invasive Fungal Infection

The EORTC/MSGERC have revised the definitions for proven, probable, and possible fungal diseases. The tissue diagnosis subcommittee was tasked with determining how and when species can be determined from tissue in the absence of culture. The subcommittee reached a consensus decision that polymerase chain reaction (PCR) from tissue, but not immunohistochemistry or in situ hybridization, can be used for genus or species determination under the new EORTC/MSGERC guidelines, but only when fungal elements are identified by histology. Fungal elements seen in tissue samples by histopathology and identified by PCR followed by sequencing should fulfill the definition of a proven fungal infection, identified to genus/species, even in the absence of culture. This summary discusses the issues that were deliberated by the subcommittee to reach the consensus decision and outlines the criteria a laboratory should follow in order to produce data that meet the EORTC/MSGERC definitions.

Johnson E, Littlechild J, Winlove CP, Vollmer F, Gow NAR. Biosensors and Diagnostics for Fungal Detection

Early detection is critical to the successful treatment of life-threatening infections caused by fungal pathogens, as late diagnosis of systemic infection almost always equates with a poor prognosis. The field of fungal diagnostics has some tests that are relatively simple, rapid to perform and are potentially suitable at the point of care. However, there are also more complex high-technology methodologies that offer new opportunities regarding the scale and precision of fungal diagnosis, but may be more limited in their portability and affordability. Future developments in this field are increasingly incorporating new technologies provided by the use of new format biosensors. This overview provides a critical review of current fungal diagnostics and the development of new biophysical technologies that are being applied for selective new sensitive fungal biosensors to augment traditional diagnostic methodologies.

Primary Cutaneous Aspergillosis in a Patient with CARD9 Deficiency and Aspergillus Susceptibility of Card9 Knockout Mice

PURPOSE

We describe a case of primary cutaneous aspergillosis caused by Aspergillus fumigatus, and elucidate the underlying genetic and immunological mechanisms.

MATERIALS AND METHODS

Routine clinical and laboratory investigations were performed. Whole-exome sequencing of the patient's DNA suggested the presence of a CARD9 mutation, which was confirmed by Sanger sequencing. Innate and adaptive immunological responses of patient-derived CARD9-deficient cells were evaluated with ELISA and flow cytometry. Cutaneous and pulmonary aspergillosis models were established in Card9 knockout (KO) mice, which were compared with wild-type and immunosuppressed mice, to explore the pathogenesis and Aspergillus susceptibility.

RESULTS

A 45-year-old man presented with a 37-year history of skin lesions on his face. A diagnosis of primary cutaneous aspergillosis was made through histopathology, immunohistochemistry, and tissue culture. Sanger sequencing of CARD9 showed a homozygous frame-shift mutation (c.819_820insG, p.D274fsX60), which led to the lack of CARD9 expression. Peripheral blood mononuclear cells from the patient showed selective impairment of proinflammatory cytokines, and Th1-, Th17-, and Th22-associated responses upon fungus-specific stimulation. The cutaneous aspergillosis model established in Card9 KO mice presented with persistent infection, with fungal germs and short hyphae in tissue, consistent with the patient's lesions. Skin lesions in immunosuppressed mice were more severe, and led to death. Unlike our patient, Card9 KO mice were relatively susceptible to pulmonary aspergillosis, with reasons to be investigated.

CONCLUSIONS

This is, to our knowledge, the first report that links cutaneous aspergillosis to CARD9 mutation. This work enriches both the phenotypic spectrum of CARD9 deficiencies and the genetic background of cutaneous aspergillosis.

Identification of infectious organisms in cytopathology: A review of ancillary diagnostic techniques

Cytology samples obtained from exfoliative sources and fine-needle aspiration (FNA) procedures can all be used to detect microorganisms and/or the associated cytopathologic effects (CPE) caused by an infection. There are many advantages to utilizing cytology samples as an adjunct to routine microbiology laboratory methods. For example, cytology samples can be obtained by non-invasive and minimally invasive techniques, and interpretation is affordable, accurate, and fast. Furthermore, routine cytology stains, including the Papanicolaou (Pap) and the Diff-Quik (DQ) stains, can adequately identify a number of microorganisms. Finally, material obtained by these procedures can also be used for cytologic ancillary testing, microbiology culture, and molecular studies. Currently, there are a variety of ancillary diagnostic techniques that are routinely utilized in the cytopathology laboratory. Additionally, the increasing utilization of molecular-based, diagnostic techniques on fluid specimens, as well as FFPE material, is expanding the role of cytopathology for infectious disease diagnostics. In this review, we provide an overview of the most practical ancillary techniques commonly used to identify microorganisms on cytology specimens.

Diagnostic performance of immunohistochemistry for the aspergillosis and mucormycosis

OBJECTIVE

To investigate the accuracy of immunohistochemistry (IHC) tests for distinguishing between mucormycosis and aspergillosis and compare the clinical characteristics of mucormycosis patients according to galactomannan (GM) results.

METHODS

We evaluated diagnostic performance of IHC test with tissue sections of patients with culture-proven invasive fungal infection. In addition, we conducted PCR assay with tissue sections of mucormycosis patients with positive GM results to evaluate the possibility of co-infection.

RESULTS

In culture-proven mucormycosis (n = 13) and aspergillosis (n = 20), the sensitivity and specificity of IHC test were both 100% for mucormycosis and 85% and 100%, respectively, for aspergillosis. Among the 53 patients who met the modified criteria for proven mucormycosis and had GM assay results, 24 (45%) were positive. Compared with those with negative GM results (n = 29), mucormycosis patients with positive GM results had significantly higher incidence of gastrointestinal tract infections (6/24 [25%] vs 0/29 [0%], P = .006) and were more likely to be histomorphologically diagnosed as aspergillosis (7/24 [29%] vs 2/29 [7%], P = .06). PCR assay amplified both Aspergillus- and Mucorales-specific DNA in 6 of these 24 cases.

CONCLUSIONS

Immunohistochemistry tests seem useful for compensating for the limitations of histomorphologic diagnosis in distinguishing between mucormycosis and aspergillosis. Some proven mucormycosis patients with positive GM results had histopathology consistent with aspergillosis and gastrointestinal mucormycosis. In addition, about one quarter of these patients revealed the evidence of co-infection with aspergillosis by PCR assay.

Diagnostic Aspects of Veterinary and Human Aspergillosis

The genus Aspergillus is composed of more than 300 species, a fraction of which are involved in animal or human infections mostly following environmental exposure. Various risk factors (i.e., immunosuppression, tuberculosis) have been recognized for human whereas for veterinary infections, unhygienic management, trauma, anatomical conformation of the skull, or suspected immunological deficiencies have been suggested. In animals, aspergillosis is mostly sporadic but in some circumstance such as infections on poultry farms may involve the whole flock. Since the high prevalence of immunosuppression in human patients has not been mirrored in veterinary medicine, and although to the best of our knowledge, no comprehensive data on the prevalence of aspergillosis in animals has been published, their epidemiology has not changed during the last decades. The impact of these infections may be economic or if they are incurable, sentimental. The objective of the first part is to describe the diagnosis of the main clinical entities caused by Aspergillus spp. in animals. It includes disseminated canine aspergillosis, canine and feline sino-nasal and sino-orbital aspergillosis, guttural pouch mycosis in horses, mycotic abortion in cattle, mycotic keratitis in horses, and avian aspergillosis. When pathogenesis and clinical aspects are relevant for diagnosis—they will be addressed as well. The second part deals with human aspergillosis, which is a multifaceted disease, manifested in a spectrum of clinical entities affecting one or more organs. Diagnosis is based on the clinical manifestation, supported and confirmed by laboratory means, involving the classical approach of demonstrating the etiological agent in the clinical specimens and in culture. Noncultural methods, such as antigen detection and/or molecular assays to detect fungal nucleic acids or protein profiles, are used as well. The isolation and identification of the fungus allows the determination of its susceptibility to antifungal drugs. Thus, antifungal susceptibility testing maybe considered as part of the diagnostic process, which is of relevance for management of the infection. In this review article, the part dealing with diagnostic aspects of aspergillosis in humans concentrates on susceptibility testing of Aspergillus spp. to antifungal drugs and drug combinations. The technologies and methods of susceptibility testing are described and evaluated.

Diagnostic Modalities for Invasive Mould Infections among Hematopoietic Stem Cell Transplant and Solid Organ Recipients: Performance Characteristics and Practical Roles in the Clinic

The morbidity and mortality of hematopoietic stem cell and solid organ transplant patients with invasive fungal infections (IFIs) remain high despite an increase in the number of effective antifungal agents. Early diagnosis leading to timely administration of antifungal therapy has been linked to better outcomes. Unfortunately, the diagnosis of IFIs remains challenging. The current gold standard for diagnosis is a combination of histopathology and culture, for which the sensitivity is <50%. Over the past two decades, a plethora of non-culture-based antigen and molecular assays have been developed and clinically validated. In this article, we will review the performance of the current commercially available non-cultural diagnostics and discuss their practical roles in the clinic.