Phenotyping SIV-infected T cells in tissues by combined immunohistochemistry and in situ hybridization for SIV RNA. As indicated by arrows, SIV-infected cells (SIV mRNA, red) are all CD3⁺ T cells (CD3⁺, blue). Also note large percentages of the infected cells (deep red) in all tissues examined are proliferating (BrdU⁺, green) which appear as either red/green or yellow/white (arrows). (A) mesenteric lymph node; (B) spleen; (C-D) intestinal organized lymphoid tissue and lamina propria, respectively. This is easier appreciated in the overlapping individual panels on the left. Also note “fuschia” colored cells in panels B and D are red blood cells that are an artifact of certain immunohistochemical techniques, and should not be interpreted as infected cells. Representative “fuschia” cells are as shown within circles in panels B and D.