What is the classic tissue morphology of Histoplasma capsulatum within macrophages?

What is the classic tissue morphology of Histoplasma capsulatum within macrophages?

• A. Small intracellular yeasts within macrophages
• B. Broad-based budding yeast
• C. Capsule halos
• D. Septate hyphae

Answer: (A)

Histoplasma capsulatum is a dimorphic fungus that, in human tissue, appears as small intracellular yeasts inside macrophages. These yeasts are about 2–4 microns in size and are often found within mononuclear phagocytes in the reticuloendothelial system, which is a characteristic scene of histoplasmosis. They bud in a narrow-based fashion and stain well with silver or PAS stains, helping you spot them inside those macrophages. This intracellular yeast form inside macrophages is what sets it apart from other fungi: Blastomyces shows larger yeasts with broad-based budding, Cryptococcus has a polysaccharide capsule that produces a visible halo, and the mold form of Histoplasma in the environment is septate hyphae with tuberculate macroconidia, not the intracellular yeast seen in tissue.

Histoplasma capsulatum is a dimorphic fungus that, in human tissue, appears as small intracellular yeasts inside macrophages. These yeasts are about 2–4 microns in size and are often found within mononuclear phagocytes in the reticuloendothelial system, which is a characteristic scene of histoplasmosis. They bud in a narrow-based fashion and stain well with silver or PAS stains, helping you spot them inside those macrophages. This intracellular yeast form inside macrophages is what sets it apart from other fungi: Blastomyces shows larger yeasts with broad-based budding, Cryptococcus has a polysaccharide capsule that produces a visible halo, and the mold form of Histoplasma in the environment is septate hyphae with tuberculate macroconidia, not the intracellular yeast seen in tissue.