FIG. 1.

Visualizing virus production by resting and activated T cells at transmission and after dissemination to lymphoid tissues.^63–65 (A) ISH to detect viral RNA within cells and virions with subsequent TSA reveals virions at the light microscopic level surrounding two kinds of virus-producing cells typed in adjacent tissue sections by combining ISH with staining for cell type and activation state. The long arrow points to a large activated CD4⁺ T cell (long arrow); the short arrow points to a smaller ostensibly resting T cell lacking markers of activation and proliferation in the cervix of a rhesus macaque following vaginal inoculation of SIV (original magnification 400 × , from reference⁶⁶). (B). Explosive virus production in a lymph node following dissemination in activated (long arrow) and resting T cells (short arrow). Image suggests clustered virus factories, where virus is efficiently transmitted to susceptible cells in close spatial proximity or through cell-to-cell transmission (long arrow) (original magnification 200 × , image unpublished). Image Credit: Wietgrefe SW and Haase AT. ISH, in situ hybridization; TSA, tyramide signal amplification.