In connective tissue staining, which component is typically seen as red?

• A. Collagen
• B. Elastin
• C. Basement membrane
• D. Smooth muscle

Answer: (A)

Collagen fibers are the component most likely to appear red in certain connective tissue stains because of how the dye interacts with the collagen structure. In Sirius Red staining, collagen binds the dye strongly, and when the section is viewed under polarized light the orderly, rope-like collagen fibers exhibit a bright red (often red-orange) birefringence. This makes collagen stand out as red, which is why it’s the chosen answer here.

Elastin, when stained with elastic stains like Verhoeff, shows up dark (black/brown) rather than red. Basement membranes are typically highlighted with PAS or other stains that yield magenta or pink tones, not red. Smooth muscle can stain a range of reds in some general stains, but the distinctive red coloration in this context is specifically characteristic of collagen with the Sirius Red/polarized light approach.