HIV-1, macrophages, glial cells, and cytokines in AIDS nervous system disease

Hallmarks of central nervous system (CNS) disease in AIDS patients are headaches, fever, subtle cognitive changes, abnormal reflexes, and ataxia. Dementia and severe sensory and motor dysfunction characterize more severe disease. Autoimmune-like peripheral neuropathies, cerebrovascular disease, and brain tumors are also observed. Histological changes include inflammation, astrocytosis, microglial nodule formation, and diffuse de- or dysmyelination. Focal demyelination can also be seen. It is clear that AIDS-associated neurological diseases are correlated with greater levels of HIV-1 antigen or genome in tissues. In AIDS dementia, macrophages and microglial cells of the CNS are the predominant cell types infected and producing HIV-1. However, manifestations of the disease make it unlikely that direct infection by HIV-1 is responsible. It seems more likely that the effects are mediated through secretion of viral proteins or viral induction of cytokines that bind to glial cells and neurons. HIV-1 induction of such cytokines as interleukin 1 (IL 1) and tumor necrosis factor-alpha (TNF alpha) may lead to an autocrine feedback loop involving further productive virus replication and induction of other cytokines such as interleukin 6 (IL 6) and granulocyte-macrophage colony-stimulating factor (GMCSF). Interleukin 1 and TNF alpha in combination with IL 6 and GMCSF could account for many clinical and histopathological findings in AIDS nervous system diseases. As HIV-1 infected patients produce elevated levels of IL 1, TNF alpha, and IL 6, it will be important to make a formal connection between the presence of these factors in the CNS, which are all products of activated macrophages, astroglia, and microglia, their in vivo induction directly by virus or indirectly by virus-induced intermediates, and the clinical and pathological conditions seen in the nervous system in this disease.