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

Abstract We investigated the histological features of lymph nodes, focusing on monocytes/macrophages, in rhesus monkeys ( Macaca mulatta ) acutely infected with simian immunodeficiency virus (SIV). In monkeys infected with a pathogenic SIV, SIVmac239, MAC387 + newly blood-derived macrophages markedly increased in number at paracortical areas at 11 to 14 days postinoculation, concomitant with the peak of the primary SIV antigenemia. The MAC387 + macrophages densely gathered around high endothelial venules and formed cell clusters with CD3 + T lymphocytes, tingible body macrophages, and plasmacytoid monocytes. In the cell clusters, CD3 + T lymphocytes which closely adhered to the MAC387 + macrophages enlarged in size, suggesting a histological manifestation of T-lymphocyte activation by macrophages. By 54 days postinoculation, when SIV antigenemia became undetectable, the MAC387 + macrophages decreased in number and the cell cluster disappeared from paracortical areas. In contrast, the monkeys infected with a nef -deleted mutant of SIVmac239 showed lower levels of SIV antigenemia and lower numbers of MAC387 + macrophages in paracortical areas than those infected with SIVmac239. These results indicate that MAC387 + macrophages accumulate in paracortical areas for the period of the intense primary SIV antigenemia and may play an important role in activating naive T lymphocytes.