In situ expression of TdT in human tonsil.

(A) Immunohistochemistry with a TdT-specific antiserum (note red-brown staining) shows strong nuclear labeling of cortical thymocytes in a human thymus. (B) Scattered TdT-positive cells are also detected in bone marrow. (C, D) Immunohistology with a TdT-specific reagent (note red nuclear labeling) reveals numerous TdT-positive cells at the boundary between lymphoid tissue and fibrous scaffold at (C) low and (D) high power (arrows indicate fibrous tissue in C and D). (E, F) In a different case, TdT-positive cells are present in the vicinity of a germinal center (GC) at (E) low power and (F) high power. Note the presence of isolate-labeled cells at the edge of a germinal center in F (arrow).