In vivo cytolysis and fusion of human immunodeficiency virus type 1-infected lymphocytes in lymphoid tissue

Lymphoid tissue was examined to see whether in vivo cytopathic effects of h uman immunodeficiency virus (HIV) infection on lymphocytes could be detecte d. Transmission electron microscopy of mechanical suspensions prepared from lymph nodes showed both replication and phagocytosis of HIV particles by m acrophages, Phagosomes contained cellular debris and virions, some of which were undergoing digestion. Neutrophils also contained HIV particles interm ixed with cellular debris in phagosomes. Immunohistochemistry revealed whol e Gag p24-positive lymphocytes and p24-positive cellular debris within the cytoplasm of paracortical macrophages. Lysing p24-positive lymphocytes were also seen. In the paracortex, p24-positive multinucleated lymphocytes with up to 5 nuclei were seen. In situ hybridization for HIV RNA in combination with immunohistochemistry for HAM56, a macrophage-specific marker, reveale d colabeled cells. Thus, HIV-positive lymphocytes undergo lysis in lymphoid tissue. The cellular debris is phagocytized by macrophages, which themselv es can replicate HIV. HIV-positive lymphocytes fuse in lymph nodes to form multinucleated cells.