Table 4.

Reactive conditions showing a normal^* pattern of PD-1 expression

Diagnosis	N	Description of PD-1 Staining
Reactive lymphoid tissue	15	PD-1-positive Tfh cells are present along the periphery of germinal centers
Reactive lymphoid tissue with follicle lysis	11	PD-1-positive Tfh cells are restricted to germinal centers. There is no increase in PD-1 staining in areas of follicle lysis
Cat Scratch Disease	4	No PD-1 reactivity associated with granulomas or abscesses
Kikuchi Lymphadenitis	5	No PD-1 reactivity associated with necrotizing areas
Castleman Disease	14	Few PD-1-positive cells are present within atrophic follicles

Abbreviations: Tfh – follicular helper T-cells; N – number of cases studied.

^*A normal PD-1 staining pattern refers to the presence of PD-1-positive cells that are essentially localized within germinal centers of secondary follicles.