Back to Unit Page Unit Textbook Chapter Animations & Images Expert Interview Transcripts Unit Glossary Related Resources View Text Only List Animations Immune System Overview An overview of the specific immune system. View Quicktime Movie HIV Infection A description of HIV structure and how it infects T cells. View Quicktime Movie HIV Receptors The two distinct co-receptors on the surface of T cells are CXCR4 and CCR5, both requiring CD4 for the entry of the HIV virus. CCR5 is the receptor used for entry in the asymptomatic phase; during the symptomatic phase the viruses can use the CXCR4 receptor. View Animation Still HIV DNA Vaccine A brief description of how DNA might be used as a vaccine for HIV. View Quicktime Movie Images A cytotoxic T cell attacking a host cell that is expressing foreign antigens Binding by both the antigen and an MHC molecule initiates the secretion of lytic enzymes by the cytotoxic T cell (Tc). Budding HIV viruses HIV-1 by transmission electron micrograph, showing mature virus particles budding from a lymphocyte Helper T cells regulate both humoral and cellular immunity A specialized macrophage ingests foreign antigens and displays antigen fragments along with MHC (self) molecules on its surface. A helper T cell (TH) with the appropriate receptor binds and responds by producing cytokines that stimulate antigen specific B cells, as well as specific cytotoxic T cells. HIV viruses HIV-1 by transmission electron microscopy, showing the mature virus particles that have budded off the nearby lymphocyte Stained HIV viruses HIV-1 by transmission electron microscopy, stained with ruthenium red to show the surface glycoprotein knobs The replication cycle of HIV 1) Membranes of the virus and the host cell fuse, and viral RNA and reverse transcriptase enter the hostçs cytoplasm. 2) Reverse transcriptase allows viral RNA to be copied to DNA. 3) Viral DNA is incorporated into the host chromosome as provirus. 4) Transcription and translation of viral proteins: viral RNA becomes incorporated into viral particles and is transcribed as well. 5) Viral particles bud out of the host cell, acquiring an envelope in the process. The structure of HIV Shows the binding of HIV to a host cell. GP-120 on the virus binds CD4 receptors on the host. A second coreceptor molecule on the host is also required for binding. Typical progression of HIV infection and AIDS

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