The dendritic cell-T cell milieu of the lymphoid tissue of the tonsil provides a locale in which SIV can reside and propagate at chronic stages of infection.

Previous studies described the presence of numerous human immunodeficiency virus (HIV)-positive cells within and just beneath the mucosal surfaces of the tonsillar tissue of HIV-1-infected individuals. The virus-positive cells were most abundant in the dendritic cell (DC)-T cell rich areas of the lymphoepithelia lining the crypts, and consisted of multinucleated syncytia that contained DCs. This suggested that such cells within the tonsillar tissue might represent a site for chronic virus replication in infected individuals. Using the simian immunodeficiency virus (SIV)-macaque system, we chose to study further the viral distribution within the tonsillar tissue of animals infected via the vaginal route 8-10 months earlier. Our initial studies demonstrated that in situ hybridization (ISH)-positive DCs and T cells could be identified within the genital mucosa and draining lymph nodes of these infected animals even at this chronic stage of infection. Here we specifically examined the distal mucosa-associated lymphoid tissues of the tonsil. ISH-positive cells were mostly restricted to the DC-rich T cell areas of the underlying lymphoid tissue. However, T cells were the most commonly infected cell type and virus-positive cells were rarely found within the epithelia. In isolated cell suspensions, ISH-positive lymphocytes were often tightly associated with ISH-negative DCs, although few ISH-positive lymphocytes were often tightly associated with ISH-negative DCs, although few ISH-positive DCs could be identified within these clusters. Therefore, the naturally occurring DC-T cell milieu of the lymphoid tissue of the tonsil provides a locale in which SIV can reside and propagate on a chronic basis, even many months after the animals were infected by virus crossing the genital mucosa.