Which markers showed brown chromophore staining in the lamina propria and epithelium to differentiate feline small cell lymphoma from inflammatory bowel disease?

• A. CD3+ and CD21
• B. CD11b+ alone
• C. NF-κB only
• D. CD11b+ and NF-κB

Answer: (D)

Immunohistochemical staining helps distinguish feline small cell lymphoma from inflammatory bowel disease by showing which cell types or pathways are active in the mucosa. Brown chromophore staining indicates positive labeling with the selected marker. In inflammatory bowel disease, you expect engagement of macrophages (CD11b+) in the lamina propria and activation of inflammatory signaling pathways (such as NF-κB) in both immune cells and epithelial cells. This combination—CD11b+ macrophages plus NF-κB activity—produces a characteristic brown staining pattern in the lamina propria and epithelium that aligns with chronic inflammatory processes rather than neoplastic lymphocytic infiltration. Small cell lymphoma, being a clonal T-cell process (often CD3+), would not inherently require concurrent macrophage-rich staining or NF-κB activation in the same mucosal pattern, so the dual presence of CD11b+ and NF-κB is the more informative indicator to differentiate the inflammatory condition from lymphoma.