Accumulation of MAC387(+) macrophages in paracortical areas of lymph nodesin rhesus monkeys acutely infected with simian immunodeficiency virus

We investigated the histological features of lymph nodes, focusing on monoc ytes/macrophages, in rhesus monkeys (Macaca mulatta) acutely infected with simian immunodeficiency virus (SIV). In monkeys infected with a pathogenic SIV, SIV mac239, MAC387(+) newly blood-derived macrophages markedly increas ed in number at: paracortical areas at 11 to 14 days postinoculation, conco mitant with the peak of the primary SIV antigenemia. The MAC387(+) macropha ges densely gathered around high endothelial venules and formed cell cluste rs with CD3(+) T lymphocytes, tingible body macrophages, and plasmacytoid m onocytes. In the cell clusters, CD3(+) T lymphocytes which closely adhered to the MAC387(+) macrophages enlarged in size, suggesting a histological ma nifestation of T-lymphocyte activation by macrophages. By 54 days postinocu lation, when SIV antigenemia became undetectable, the MAC387(+) macrophages decreased in number and the cell cluster disappeared from paracortical are as, In contrast, the monkeys infected with a nef-deleted mutant of SIV mac2 39 showed lower levels of SIV antigenemia and lower numbers of MAC387(+) ma crophages in paracortical areas than those infected with SIV mac239. These results indicate that MAC387(+) macrophages accumulate in paracortical area s for the period of the intense primary SIV antigenemia and may play an imp ortant role in activating naive T lymphocytes. (C) 1999 Editions scientifiq ues et medicales Elsevier SAS.