Piringer’s lymphadenopathy. (a) CD3 immunostaining: the monocytoid B-cell zone is nearly devoid of T cells, in contrast to the follicle mantle and germinal center. (b) BCL-2 immunostaining: monocytoid B cells are negative for BCL-2. (c) Ki-67 immunostaining: approximately 10% to 20% of the monocytoid B cells are in cell cycle. (d) CD21 immunostaining. Note the labeling of follicular dendritic cells within the germinal center and their absence from the monocytoid B-cell zone. MCB, monocytoid B cells; FM, follicle mantle; GC, germinal center.