CD86 immunohistochemical staining for the detection of Talaromyces marneffei in lesions

Talaromycosis is an invasive fungal disease caused by the pathogenic thermodimorphic fungus Talaromyces marneffei (TM), which is often overlooked in tropical and subtropical regions of Asia. In view of the diversity of clinical manifestations in patients with TM infection, early diagnosis remains challenging. We assessed the sensitivity and specificity of a novel immunohistochemical staining by performing CD86 immunohistochemical staining on 56 tissue sections from patients with talaromycosis who had fungal culture or metagenomic next-generation sequencing confirmed to exist in clinical specimens, as well as 26 patients with other fungi that had been culture-proven. Hematoxylin and eosin and periodic acid Schiff (PAS) stains were also applied to each specimen. We found that anti-CD86 antibody can label TM pathogens in 38 HIV-negative specimens (38/42) and 14 HIV-positive specimens (14/14); conversely, PAS staining yielded positive results in seven cases of HIV-negative specimens (7/42) and 13 cases of HIV-positive specimens (13/14). Additionally, CD86 immunohistochemical staining was negative in other fungi. Importantly, CD86 immunohistochemical staining significantly outperformed PAS staining in terms of localizing and highlighting TM yeasts, as well as demonstrating the specificity of 100% and a significantly higher sensitivity compared to PAS staining at 92.9% versus 35.7% (P < 0.05, McNemar test). Our findings suggest that CD86 immunohistochemical staining has the potential for the rapid diagnosis of talaromycosis.IMPORTANCETalaromycosis is an opportunistic endemic disease without typical clinical manifestations that has emerged as a fungal disease impacting the survival and mortality of immunocompromised individuals and HIV-positive individuals in endemic regions. Nonetheless, talaromycosis is completely curable if it is accurately diagnosed and treated effectively at an early stage. Rapid pathological diagnosis relies on the unique morphological features of Talaromyces marneffei observed under the microscope. This study introduces a novel pathological diagnostic approach, CD86 immunohistochemical staining, to enhance the early detection of TM-infected lesions.