Cellular localization of simian immunodeficiency virus in lymphoid tissues. II. In situ hybridization.

Lymph nodes and spleens were collected at autopsy and by biopsy from 29 rhesus monkeys infected with simian immunodeficiency virus (SIV). Lymph nodes were classified morphologically into stages of follicular hyperplasia, follicular involution, follicular depletion with normal or expanded paracortices, follicular and paracortical depletion, granulomatous lymphadenitis, or normal. The distribution of SIV RNA was determined by in situ hybridization using a nick translated, 35S labeled, SIVmac DNA probe. Numbers of SIV-infected cells were rare during follicular hyperplasia, numerous during follicular and paracortical expansion, and rare during follicular and paracortical depletion. The splenic morphology reflected that of the lymph nodes; however, the numbers of SIV-positive cells were uniformly lower. SIV RNA was frequently restricted to a single nucleus within multinucleate syncytial cells in two cases of granulomatous lymphadenitis. These results, combined with those of a previous study, provide evidence for antigen trapping in SIV-infected hyperplastic lymph nodes and for widespread viral infection of macrophages and lymphocytes during paracortical expansion.