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Updated: Aug 8, 2026
Passive Administration of Monoclonal Antibodies Against H. capsulatum and Others Fungal Pathogens
Published on: February 15, 2011
Comparison of an established antibody sandwich method with an inhibition method of Histoplasma capsulatum antigen
T O Garringer1, L J Wheat, E J Brizendine
1Departments of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA. TGARRING@IUPUI.EDU
Insights
A new inhibition assay for Histoplasma antigen detection showed similar sensitivity to the standard antibody sandwich method but lower specificity and reproducibility, especially with control samples. This suggests the inhibition assay is less precise for diagnosing histoplasmosis.
Area of Science:
- Immunodiagnostics
- Mycology
- Infectious Diseases
Background:
- Histoplasmosis is a severe fungal infection diagnosed using antigen immunoassays.
- Antibody sandwich assays are standard, but inhibition assays offer potential advantages like reduced antibody use.
- This study evaluates a newly developed inhibition assay against the established sandwich method.
Purpose of the Study:
- To compare the diagnostic performance of a novel Histoplasma antigen inhibition assay with a standard antibody sandwich assay.
- To assess sensitivity, specificity, and reproducibility of both methods in urine and serum samples.
- To identify potential cross-reactivity with other fungal pathogens.
Main Methods:
- Developed an inhibition assay using a polyclonal antibody.
- Tested urine and serum from patients with culture-proven histoplasmosis and controls using both inhibition and antibody sandwich assays.
- Analyzed sensitivity, specificity, reproducibility, and cross-reactivity.
Main Results:
- Both methods demonstrated similar sensitivity for detecting Histoplasma antigen in urine and serum.
- The antibody sandwich assay showed superior specificity in urine (97.5% vs. 80.0%) and comparable specificity in serum.
- The inhibition assay exhibited fair to poor reproducibility with control specimens, while the sandwich assay showed good reproducibility.
Conclusions:
- The inhibition assay has limitations in specificity and reproducibility compared to the antibody sandwich method, particularly at lower detection ranges.
- The established antibody sandwich assay remains a more reliable method for diagnosing histoplasmosis.
- Cross-reactivity was observed with other fungal infections, indicating a need for further assay refinement.
Abstract:
The Histoplasma antigen immunoassay utilizes an antibody sandwich method that provides a rapid and reliable means of diagnosing the more severe forms of histoplasmosis. Inhibition assays have been developed for antigen detection and offer at least one potential advantage, namely, reduced antibody requirements. We have developed an inhibition assay using the polyclonal antibody employed in our standard sandwich assay. Urine and serum specimens from patients with culture-proven histoplasmosis and controls were tested using both methods. The two methods had similar sensitivities for detection of antigen in urine (antibody sandwich = 92.5% versus inhibition = 87.5%, P = 0.500) and serum (82.5% versus 80.0%, P = 1. 000). With serum, the specificities of both methods were similar (antibody sandwich assay = 95.0% versus inhibition assay = 92.5%, P = 1.000), and with urine, the specificity of the antibody sandwich method was superior (97.5% versus 80.0%, P = 0.039). While the overall reproducibility of both methods was excellent (with urine, antibody sandwich assay intraclass correlation coefficient = 0.9975 and with serum = 0.9949; correlation coefficient of the inhibition assay with urine = 0.9736 and with serum = 0.9850), that of the inhibition method was only fair to poor for the controls: urine = -0. 0152, serum = 0.5595. Reproducibility was good for the controls using the sandwich method: urine = 0.7717, serum = 0.9470. Cross-reactivity was observed in specimens from patients infected with Blastomyces dermatitidis, Paracoccidioides brasiliensis, and Penicillium marneffei. In conclusion, the decreased specificity and inferior reproducibility with control specimens suggest that the inhibition assay has poorer precision toward the lower end of the detection range.
