Whole Body Positron Emission Tomography Imaging of Activated Lymphoid Tissues during Acute Simian–Human Immunodeficiency Virus 89.6PD Infection in Rhesus Macaques

Abstract Mechanisms of acute retroviral pathogenesis have been examined during primary infection of rhesus macaques with simian–human immunodeficiency virus 89.6PD (SHIV 89.6PD ). During acute infection, between initial exposure and establishment of antigen-specific immune responses that stabilize the virus burden, rapid immune system changes influence the viral set-point and dictate subsequent steps in disease progression. In a previous study, we described specific patterns of lymphocyte activation during acute SHIV 89.6PD infection. We now extend these studies to describe lymphoid tissue activation, using whole body positron emission tomography (PET) and the radioactive tracer 2-[ 18 F]fluorodeoxyglucose (FDG). Within a few days after primary infection by intravenous, intrarectal, or intravaginal routes, PET–FDG imaging revealed a distinct pattern of lymphoid tissue activation centered on axillary, cervical, and mediastinum lymph nodes. Increased tissue FDG uptake preceded fulminant virus replication at these sites, suggesting that a diffusible factor of host or viral origin was responsible for lymphoid tissue changes. These data show that activation of lymphoid tissues in the upper body is an early response to virus infection and that diffusible mediators of activation might be important targets for vaccine or therapeutic intervention strategies.