Schematic comparison of classical GC, PTGC, and LPHD.

Shown are a classical GC, 2 PTGCs, and 2 follicular structures in an LPHD lymph node. Depicted are the main B-cell types in these structures, namely naive B cells (ie, mantle zone cells in the classical GC), centroblasts, centrocytes, memory B cells, and lymphocytic and histiocytic cells of LPHD. T-helper cells and follicular dendritic cells, which are present in each of the 3 structures, are not shown. Ongoing somatic hypermutation in the lymphocytic and histiocytic cells has been observed in approximately half the patients. The composition of the population of small resting B cells in the LPHD is hypothetical.