Immunophenotype of interfollicular neoplastic B cells in frozen sections of follicular lymphoma. (A-F) Serial sections of case 6 immunostained for CD20 (A), CD10 (B), Ig κ light chain (C), Ig λ light chain (D), CD38 (E), and CD95 (F). The interfollicular zone contains an Ig λ light chain restricted B-cell population. CD10, CD38, and CD95 are expressed by the neoplastic follicle but not by the neoplastic B cells of the interfollicular zone. (G,H) Sections of case 1 immunostained for CD80 (G) and case 2 for CD86 (H) show that CD80 and CD86 are expressed in the follicles but are downregulated in the interfollicular zone. (A-H, immunoperoxidase)