Illustrative lymph node histopathology in ALPS-FAS. (A) Paracortical expansion, which is typical for ALPS. Arrows point to reactive follicles. Lower panel showing higher-power view of the cellular composition of the paracortex, bottom arrow showing reactive follicle. (B) Immunohistochemistry showing CD3, CD4, and CD8 stain to highlight presence of double-negative T cells in the paracortical expansion. Bottom left panel shows reactive B-cell follicle (CD20).