An interferon gamma release assay specific for Histoplasma capsulatum to detect asymptomatic infected individuals: A proof of concept study

Abstract

Histoplasmosis is the most common endemic mycosis in the Americas. Currently, there is no laboratory test capable to detect subclinical or latent infections by Histoplasma capsulatum (Hc), which might develop as severe infections in immunocompromised individuals. For the first time to our knowledge, we explore the suitability of an interferon gamma release assay (IGRA) to detect latent Hc infection in asymptomatic individuals. A cohort of 126 volunteers was enrolled in the study, 13 of which underwent a Hc infection in the past, and 93 of them showing risk factors for this infection. The remaining 20 participants did not refer any risk factors of Hc infection, but eight of them showed evidences of infection with Mycobacterium tuberculosis. All participants were recruited in Medellin, Colombia, between January 2014 and December 2017. Whole blood samples were cultured with four different Hc crude antigens and phytohemaglutinin as positive control. The interferon (IFN)-γ released by T lymphocytes upon antigen stimulation was quantified by ELISA. A defined cutoff value of 20 pg/ml for the IFN-γ concentration allowed us to distinguish between the group with documented past infections and the group of noninfected individuals with high sensitivity (70–92%) and specificity (85–95%), for the four tested antigens. Positive 82–95% and negative 77–92% predictive values were also very high, comparable to those reported for commercially available IGRAs. The new test constitutes a promising screening method to detect individuals with latent Hc infection, even decades after the primary infection, as evidenced in this study.

Development of a Simple and Robust Whole Blood Assay with Dual Co-Stimulation to Quantify the Release of T-Cellular Signature Cytokines in Response to Aspergillus fumigatus Antigens

“…To overcome these drawbacks, there is a growing interest in the development of whole blood (WB)-based protocols to determine T-cell responses to fungal antigens [15,16], following the clinical success of WB-based tests in tuberculosis and cytomegalovirus (CMV) diagnostics and research [17][18][19]. Although WB assays are more robust than PBMCbased protocols [16], concerns about impaired test performance remain when stimulation conditions are suboptimal, e.g., in the presence of immunosuppressive therapy or after long pre-analytic delays [16,[20][21][22][23].…”

Current Concepts in the Epidemiology, Diagnosis, and Management of Histoplasmosis Syndromes

“…A H. capsulatum interferon gamma release assay demonstrated high sensitivity and specificity, allowing discrimination between latently infected and noninfected individuals. 64 A matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF MS) reference database for the identification of H. capsulatum has been developed; MALDI-TOF MS could reduce time to identification and also decrease risk to laboratory personnel cultivating the fungus. 65…”

Timely Diagnosis of Histoplasmosis in Non-endemic Countries: A Laboratory Challenge

“…Efforts, however, are under way. A Colombian group is working on the development of an IGRA-based assay with promising preliminary results, and a huge potential for the diagnosis of subclinical infections regardless of the immune status of the host (Rubio-Carrasquilla et al, 2019); more results are awaited. A lateral flow device (LFD) for the detection of Histoplasma antigen in serum has been developed recently showing an excellent sensitivity, and extensive validation in non-progressive disseminated cases is expected (Cáceres et al, 2019).…”