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1、,Lesson NineWhat We Know About AIDS,What is HIV?HIV(human immunodeficiency virus)is the virus that causes AIDS.This virus is passed from one perso n to another through blood-to-blood and sexual contact.In addition,infected pregnant women can pass HIV to their baby during pregnancy or delivery,as wel
2、l as through breast-feeding.People with HIV have what is called HIV infection.Most of these people will develop AIDS as a result of their HIV infection.,What is AIDS?What causes AIDS?AIDS stands for acquired immunodeficiency syndrome.An HIV-infected person receives a diagnosis of AIDS after developi
3、ng one of the CDC-defined AIDS indicator illnesses,(opportunistic infection.)An HIV-positive person who has not had any serious illnesses also can receive an AIDS diagnosis on the basis of certain blood tests(CD4+counts).A CD4+count of less than 200 indicates a severely damaged immune system and an
4、AIDS diagnosis.,A positive HIV test result does not mean that a person has AIDS.A diagnosis of AIDS is made by a physician using certain clinical criteria.Infection with HIV can weaken the immune system to the point that it has difficulty fighting off certain infections.These types of infections are
5、 known as opportunistic infections because they take the opportunity a weakened immune system gives to cause illness.,Many of the infections that cause problems or may be life threatening for people with AIDS,are usually controlled by a healthy immune system.The immune system of a person with AIDS i
6、s weakened to the point that medical intervention may be necessary to prevent or treat serious illness.Today there are medical treatments that can slow down the rate at which HIV weakens the immune system.There are other treatments that can prevent or cure some of the illnesses associated with AIDS.
7、As with other diseases,early detection offers more options for treatment and preventative care.,Also,once a person is diagnosed with AIDS,they will always be considered to have AIDS,regardless of clinical changes later on.For example,if a person has HIV and a CD4 count below 200,they are considered
8、to have AIDS.If their CD4 count later goes back to above 200,they are still considered to have AIDS.,Word Formation abbreviation n.From the verb“abbreviate”:write the short form of a word contaminate v.contamination n.contaminant:a substance that can make dirt follicular a.from its noun“folliculus”f
9、olliculi pl.dendritic a.from its noun“dendrite”homosexual:homo-:(same)+sexual homobody;homoplastic;homotoxin,hetero-:other heteroantibody;heteroantigen;heterostimulation heterotopia;heterotransplantation lymphocytic a.from“lymphocyte”leukocyte:white blood cell erythrocyte:red blood cell thrombocyte:
10、platelet,I.Topics for Class Discussion:1.What is the main idea of Paragraph 1?2.How is AIDS transmitted?3.Whats the main idea of Paragraph 3?4.Who can be easily infected by HIV-1 strain?5.How is HIV-2 spread?6.Whats the main idea of Paragraph 5?7.Whats the main idea of Paragraph 6?8.How does HIV dam
11、age the immune system?9.Whats the main idea of last paragraph?,II.Language Points:1.prey to:1)n.+to(be/become/fall prey to):be greatly troubled by e.g.Some people with disordered mind become a prey to fears of being murdered.2)v.+on e.g.His worries preyed on his mind.Ill health preyed on him for man
12、y years.,2.deteriorate v.become worse in quality e.g.Renal function begins to deteriorate.The patients condition has deteriorated since bat v.fight,struggle e.g.The doctors are concentrating their efforts on combating cancers.The inflammatory response is essential in combating most infections.,4.a s
13、uccession of:e.g.A succession of strange things happened here last month.A succession of cross infections in the ward let him to death.5.integrate with:combine withe.g.I integrated your suggestion with my plan.The school integrates maths lessons with computer studies.,*integrate into:e.g.He tried to
14、 integrate all their activities into one program.,Human Immunodeficiency Virus(HIV):Overview Human Immunodeficiency Virus(HIV)presents a complex knot for scientists to unravel.After initial contact and attachment to a cell of the immune system(e.g.lymphocytes,monocytes),there is a cascade of intrace
15、llular events.The endproduct of these events is the production of massive numbers of new viral particles,death of the infected cells,and ultimate devastation of the immune system.,However,the knot IS becoming unraveled.These pages attempt to simplify HIV infection at the cellular level.The following
16、 diagram shows a number of steps from initial attachment of a viral particle to a lymphocyte through budding of new viruses from that cell.,Attachment to the Lymphocyte Membrane On the surface membrane of all living cells are complex protein structures called receptors.A receptor is often compared t
17、o a lock into which a specific key or ligand will fit.There are at least two receptors on T-lymphocytes to which the human immunodeficiency virus(HIV)sticks.The primary receptor,called CD4,is shown on the right in the diagram.But a second receptor that loops through the cell membrane 7 times is crit
18、ical for infection to occur.,HIV infection of a lymphocyte requires attachment of the virus to the cell membrane through both of these ligand-receptor links.In cells whose 7-transmembrane receptor is different,the HIV key no longer matches the lymphocyte lock and attachment is incomplete.Those cells
19、 may avoid infection by HIV.Tight attachment of the viral particle to receptors on the lymphocyte membrane enables fusion with the cell membrane.The viral contents,including viral RNA(shown in yellow)then empty into the cells cytoplasm.Like other viruses that infect human cells,HIV commandeers the h
20、osts machinery to make multiple copies of itself.,Integration of Viral DNA Once the viral RNA has been reverse-transcribed into a strand of DNA,the DNA can then be integrated(inserted)into the DNA of the lymphocyte.The virus has its own enzyme called integrase that facilitates incorporation of the v
21、iral DNA into the host cells DNA.The integrated DNA is called a provirus.,Transcription:Back to RNA As long as the lymphocyte is not activated or turned-on,nothing happens to the viral DNA.But if the lymphocyte is activated,transcription of the viral DNA begins,resulting in the production of multipl
22、e copies of viral RNA.This RNA codes for the production of the viral proteins and enzymes(translation)and will also be packaged later as new viruses.,Translation:RNA-Proteins There are only 9 genes in the HIV RNA.Those genes have the code necessary to produce structural proteins such as the viral en
23、velope and core plus enzymes like reverse transcriptase,integrase,and a crucial enzyme called a protease.,Viral Protease When viral RNA is translated into a polypeptide sequence,that sequence is assembled in a long chain that includes several individual proteins(reverse transcriptase,protease,integr
24、ase).Before these enzymes become functional,they must be cut from the longer polypeptide chain.Viral protease cuts the long chain into its individual enzyme components which then facilitate the production of new viruses.,Protease Inhibitors Inhibitors of this viral protease can be used to fight HIV
25、infection.By blocking the ability of the protease to cleave the viral polypeptide into functional enzymes,protease inhibitors interfere with continued infection.Mutations enable HIV to avoid treatments that involve only one drug,so there is growing use of multiple-drug therapies in which both a prot
26、ease inhibitor AND a reverse transcript inhibitor are combined.,Reverse Transcription:Converting viral RNA into DNA An enzyme(protein)thats part of the human immunodeficiency virus reads the sequence of viral RNA nucleic acids that have entered the host cell and transcribes the sequence into a complementary DNA sequence.That enzyme is called reverse transcriptase.Without reverse transcriptase,the viral genome couldnt become incorporated into the host cell,and couldnt reproduce.,
