Observational study in Sudan finds few immune differences in mycetoma species

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medRxiv Published April 16, 2026 Medically reviewed April 25, 2026 Study authors: Osman, M.; Ashwin, H.; Calder, G.; O'Toole, P.; Bakhiet, S. M.; Musa, A. M.; Kaye, P. M.; Fahal, A. … DOI ↗ By Dr. Amelia Tan, PhD · Internal Medicine & Chronic Disease

Key Takeaway

Note preliminary immune marker findings in mycetoma; interpret cautiously due to small sample.

This publication is a research article reporting an observational study conducted in Sudan, involving 11 patients with mycetoma. The study examined surgical biopsies from patients with bacterial mycetoma (caused by Actinomadura pelletierii and Streptomyces somaliensis) and fungal mycetoma (caused by Madurella mycetomatis), focusing on the distribution of 43 immune-related proteins and cellular infiltrate expression. No comparator was reported, and follow-up duration was not specified.

The key findings indicate few significant differences in immune marker expression across the different mycetoma species and pathogen classes, with effect sizes, absolute numbers, p-values, and confidence intervals not reported. However, the study observed higher per-cell expression of CD66b+, ARG1, and VISTA in cellular infiltrates closest to grain boundaries, though the magnitude and statistical significance of this increase were not detailed. Safety data, including adverse events and tolerability, were not reported.

Limitations noted by the authors include a paucity of information on immune responses in mycetoma patients, which may affect the generalizability of the results. The small sample size of 11 patients and lack of quantitative effect measures further constrain the certainty of the findings. Practice relevance was not reported, so these results should be interpreted cautiously as exploratory insights into mycetoma immunology, requiring validation in larger studies.

Study Details

Sample sizen = 6

EvidenceLevel 5

PublishedApr 2026

View Original Abstract ↓

Mycetoma is a neglected tropical disease caused by various bacterial and fungal pathogens that has a significant health impact across a broad geographically defined "mycetoma belt" spanning South America, Africa and Asia. Histologically, mycetoma is characterised by invasive and destructive granuloma development in the skin, deep tissues and bone, leading to tissue destruction, deformities and high morbidity. The presence of macroscopic, highly compacted pathogen microcolonies, or "grains," is a key diagnostic feature, and the formation of grains supports pathogen persistence and disease chronicity. However, there is a paucity of information on immune responses in mycetoma patients and on the relative importance of phylogeny and/or grains in establishing the local immune landscape. Here, we used spatial proteomics to examine the distribution of 43 immune-related proteins in surgical biopsies from 11 patients with mycetoma of bacterial (Actinomycetoma; Actinomadura pelletierii and Streptomyces somaliensis; n=6) and fungal (Eumycetoma; Madurella mycetomatis; n=5) origin. Using mixed-effects modelling, an exploratory analysis across species and pathogen classes revealed few significant differences in immune marker expression. In contrast, and independently of pathogen class, the cellular infiltrate closest to grain boundaries had higher per-cell expression of CD66b+, ARG1, and VISTA. The preferential accumulation of CD66b+ARG1+VISTA+ cells at grain boundaries was confirmed by quantitative immunofluorescence analysis. Hence, the local tissue microenvironment surrounding the mycetoma grain represents a specialised immunosuppressive niche, with parallels to the tumour microenvironment.