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Yeast Infection Emedicine

HIV AIDS signs symptoms transmission pathophysiology

HIV, or human immunodeficiency virus, is avirus that targets cellsthe immune system. Over time, the immune system begins to failwhich is called immunodeficiency, and this increases the risk of infections and tumorsthat a healthy immune system would usually be able to fend off. These compliions arereferred to as AIDS, or acquired immunodeficiency synome. Now there are two distinct types of HIV—HIV1and HIV2. HIV1 is the more commonly associated with AIDSthe US and worldwide, HIV2 ismore rare, and typically restricted to areaswestern Africa and southern Asia. HIV2is so uncommon that “HIV� almost always

refers to HIV1. Alright HIV targets CD4+cells, meaning cells that have this specific molecule called CD4 on their membrane. Macrophages,Thelper cells, and denitic cells are all involvedthe immune response and all haveCD4 molecules; therefore they can be targeted by HIV. The CD4 molecule helps these cellsattach to and communie with other immune cells, which is particularly important whenthe cells are launching attacks against foreign pathogens. So this little molecule is prettyimportant for our immune system, but it's also extremely important for HIV. HIV targetsand attaches to the CD4 molecule via a protein called gp120 found on its envelope. HIV thenagain uses gp120 to attach to another receptor,

called a coreceptor. HIV needs to bind toboth the CD4 molecule and a coreceptor to get inside the cell. The most common coreceptorsthat HIV uses are the CXCR4 coreceptor, which is found mainly on Tcells, or the CCR5 coreceptorwhich is found on Tcells, macrophages, monocytes, and denitic cells. These coreceptors are so important that somepeople with homogeneous genetic mutationstheir CCR5 actually have resistance orimmunity to HIV, since HIV can't attach and get into the cell. In fact, even heterozygousmutations which lead to fewer coreceptors on the cells, can make it harder for the virusto spread, and resultsa slower disease

progression. For those without this mutation though, onceHIV binds to CD4 and either CCR5 or CXCR4, it gains access to the cell. HIV is a singlestranded,positivesense, enveloped RNA retrovirus, meaning that it injects its single strandof RNA into the Thelper cell. The “retro� part of retrovirus isn't referring to itsstyle, but refers to it needing to use an enzyme called reverse transcriptase to transcribea complementary doublestranded piece of “proviral� DNA. Proviral just means that it's readyto be integrated into the host's DNA, so it enters the Thelper cell's nucleus andpops itself into the cell's DNA, ready to

be transcribed into new viruses, pretty sneaky,huhé Well here's the actual sneaky part—when the immune cells become activated, they starttranscribing and translating proteins needed for the immune response. Ironically, thismeans that whenever the immune cell is exposed to something that causes it to start up animmune response, like any infection, the immune cell ends up inadvertently transcribing andtranslating new HIV viruses, which bud off from the cell membrane to infect more cells.Very sneaky indeed! One thing to know is that HIV is notoriousfor making errors when it replies and that during an infection it can mutate to createslightly different strains of viruses. These

viruses are all still considered “HIV�but behave slightly differently from each other and target different cellsthe host,in fact that host cell preference is called viral tropism. So let's start with HIV enteringthe body through sexual intercourse which is how it typically spreads from person toperson. At this early point, during what we call acute infection, the R5 strain of HIV,which bind to the CCR5 coreceptor will get into macrophages, denitic cells, and T cells.Usually denitic cells hanging outthe epithelial or mucosal tissue where the virusentered the body, capture the virus and migrate to the lymph nodes, where a lot of immunecells live, and the R5 strain of HIV essentially

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