CD4 and viral infectious disease: In addition to supporting virus replication and degrading the infecting virus, autophagy also contributes to the apoptosis of CD4+ T lymphocytes after human immunodeficiency virus (HIV) envelope proteins bind to C-X-C chemokine receptor type 4 (CXCR-4) in infected cells [394], suggesting that virus infection can trigger the HIV-induced destruction of CD4+ T cells.