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Updated: Jul 5, 2026
Passive Administration of Monoclonal Antibodies Against H. capsulatum and Others Fungal Pathogens
Published on: February 14, 2011
[Preparation and study of an exoantigen of Histoplasma capsulatum for serological reactions.]
R Negroni1, C Iovannitti, A I Arechavala
1Unidad de Micología del Hospital Francisco Javier Muñiz, Buenos Aires, Argentina. hmmicologia@intramed.net.
Abstract:
The aim of this study was to determine the usefulness of a yeast-phase exo-antigen of Histoplasma capsulatum in standard serologic reactions. Three native strains of H.capsulatum which belong to Mycology Center collection were employed. They were maintained in their yeast-phase by weekly subcultures in 2% dextrose broth agar at 37 degrees C. After one week incubation yeast cells were suspended in distilled water containing thimerosal and phenylmethyl sulfonyl fluoride at a concentration of 1:5000. This suspension was left at room temperature for 72 h, then the supernatant was separated by centrifugation and it was lyophilized. Proteins and polysaccharides concentrations were determined. Immunodiffusion (ID) tests were carried out with an antigenic dilution containing 1.4 mg/ml of proteins. This exo-antigen was submitted to SDS-PAGE. Seven protein fractions were detected but only two of them showed antigenic activity against a pool of positive human sera; the molecular weights of these two proteins were 97 kDa and 66 kDa respectively. A metabolic antigen from the mycelial phase of H. capsulatum was used as control. A rabbit gammaglobulin anti-H. capsulatum was prepared and employed as positive control in serologic reactions. The antigenic capacity of ten batches of this exo-antigen was studied by ID and counterimmunoelectrophoresis (CIE) tests using serum samples of 20 hamsters experimentally infected by intracardiac inoculation of the yeast-phase of H. capsulatum. All tests presented positive results after three weeks of the infection. Fifty sera from patients suffering progressive histopasmosis were analyzed: ID, CIE and complement fixation (CF) tests were performed in all cases. HIV negative patients presented 7/7 (100%) positive reactions with the yeast-phase exoantigen and 5/7 (71.4%) with histoplasmin. In HIV positive patients CIE and CF were the most sensitive serologic tests, they gave positive results in 15/43 cases (34.8%) with the yeast-phase exo-antigen and in 7/43 cases (13.9%) with histoplasmin. Sera from 10 patients with paracoccidioidomycosis, aspergillosis and candidiasis respectively were studied by ID with the aim of detecting serologic cross reactions. No cross reaction was detected in these serum samples. This yeast-phase exo-antigen of H. capsulatum is more sensitive than and equally as specific as control histoplasmin.
Insights
A new yeast-phase exo-antigen from Histoplasma capsulatum shows improved sensitivity and specificity for diagnosing histoplasmosis. This diagnostic tool is particularly effective in HIV-positive patients, outperforming traditional histoplasmin tests.
Area of Science:
- Mycology
- Immunology
- Medical Diagnostics
Context:
- Histoplasmosis is a significant fungal infection, often diagnosed through serologic methods.
- Current diagnostic antigens, like histoplasmin, have limitations in sensitivity and specificity, especially in immunocompromised individuals.
- Developing novel, more effective diagnostic antigens is crucial for timely and accurate histoplasmosis detection.
Purpose:
- To evaluate the diagnostic utility of a novel yeast-phase exo-antigen derived from Histoplasma capsulatum in standard serologic assays.
- To compare the sensitivity and specificity of this new antigen against the conventional histoplasmin antigen.
- To assess the performance of the yeast-phase exo-antigen in diagnosing histoplasmosis across different patient groups, including HIV-positive individuals.
Summary:
- A yeast-phase exo-antigen of Histoplasma capsulatum was prepared and characterized, revealing two immunodominant protein fractions (97 kDa and 66 kDa).
- This novel antigen demonstrated high sensitivity and specificity in immunodiffusion (ID), counterimmunoelectrophoresis (CIE), and complement fixation (CF) tests.
- The yeast-phase exo-antigen showed superior performance compared to histoplasmin, particularly in HIV-negative (100% vs. 71.4%) and HIV-positive patients (34.8% vs. 13.9% using CIE and CF).
Impact:
- The study introduces a more sensitive and equally specific diagnostic tool for histoplasmosis, improving upon existing serologic methods.
- This enhanced diagnostic capability is especially valuable for immunocompromised patients, including those with HIV, where histoplasmosis can be severe.
- The findings pave the way for improved clinical management and public health strategies for histoplasmosis through more accurate early detection.
