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AIDS and other Acquired or Secondary Immunodeficiencies – I
This Sqadia video demonstrates about AIDS and other Immunodeficiencies. Luc Montagnier in Paris and Robert Gallo in Bethesda discovered the causative agent of AIDS that is retrovirus. Retroviruses carry their genetic information in the form of RNA. When the virus enters a cell, the RNA is reverse transcribed to DNA by a virally encoded enzyme, reverse transcriptase (RT). This copy of DNA is called provirus. Only one other human retrovirus, human T-cell lymphotropic virus I, or HTLV-I, had been described before HIV-1. This retrovirus is endemic in the southern part of Japan and in the Caribbean. A small percentage of individuals develop serious illness, either adult T-cell leukemia or HTLV-I–associated myelopathy. There is also a related human virus called HIV-2, which is less pathogenic in humans than HIV-1. Viruses related to HIV-1 have been found in nonhuman primates. These viruses, variants of simian immunodeficiency virus, or SIV, cause immunodeficiency disease in certain infected monkeys. Retroviruses related to HIV-1 include the feline and bovine immunodeficiency viruses and the mouse leukemia virus. Specific information about HIV-1 cannot be gained by infecting animals because HIV-1 does not replicate in them. Only the chimpanzee supports infection with HIV-1 but infected chimpanzees only rarely develop AIDS. The SCID mouse reconstituted with human lymphoid tissue for infection with HIV-1 has been useful for certain studies of HIV-1 infection.
AIDS and other Acquired or Secondary Immunodeficiencies – II
The first step in HIV infection is viral attachment and entry into the target cell. HIV-1 infects T cells that carry the CD4 antigen on their surface; in addition, certain HIV strains will infect monocytes and other cells that have CD4 on their surface. Expression of other cell-surface molecules, coreceptors present on T cells and monocytes, is required for HIV-1 infection. The infection of a T cell is assisted by the T cell coreceptor CXCR4 (in initial reports, this molecule was called fusin). An analogous receptor called CCR5 functions for the monocyte or macrophage.
AIDS and other Acquired or Secondary Immunodeficiencies – III
After the virus has entered the cell, the integrated provirus is transcribed and the various viral RNA messages spliced and translated into proteins, which along with a complete new copy of the RNA genome are used to form new viral particles. The discovery that CXCR4 and CCR5 serve as coreceptors for HIV-1 on T-cells and macrophages. A T-tropic strain uses CXCR4, while the M-tropic strains use CCR5. This use of different coreceptors also helped to explain the different roles of cytokines and chemokines in virus replication. Both of the HIV coreceptors, CCR5 and CXCR4, function as receptors for chemokines.
AIDS and other Acquired or Secondary Immunodeficiencies – IV
HIV-1 infection of T cells with certain strains of virus leads to the formation of giant cells or syncytia. These are formed by the fusion of a group of cells. Formation of syncytia may be blocked by antibodies to some of the epitopes of the CD4 molecule, by soluble forms of the CD4 molecule and by antibodies to cell-adhesion molecules. Isolates of HIV-1 from different sources were formerly classified as syncytia-inducing (SI) or non–syncytium inducing (NSI). In most cases, these differences correlated with the ability of the virus to infect T cells or macrophages: T-tropic strains were SI, whereas M-tropic strains were NSI. Isolation of HIV-1 and its growth in culture has allowed purification of viral proteins and the development of tests for infection with the virus. The most commonly used test is for the presence of antibodies directed against proteins of HIV1. Diagnosis of AIDS includes evidence for infection with HIV-1 (presence of antibodies or virus in blood), greatly diminished numbers of CD4+ T cells (200 cells/mm3), impaired or absent delayed-hypersensitivity reactions, and the occurrence of opportunistic infections. Patients with AIDS generally succumb to tuberculosis, pneumonia, severe wasting diarrhea, or various malignancies. Primary infection in a minority of patients may be symptomatic with fever, lymphadenopathy (swollen lymph nodes), and a rash, but these symptoms generally do not persist more than a few weeks.
AIDS and other Acquired or Secondary Immunodeficiencies – V
The first overt indication of AIDS may be opportunistic infection with the fungus Candida albicans, which causes the appearance of sores in the mouth (thrush) and, in women, a vulvovaginal yeast infection that does not respond to treatment. A persistent hacking cough caused by P. carinii infection of the lungs may also be an early indicator. HIV infected individuals are classed into 3 categories i.e. Category A, Category B, and Category C. Category A is asymptomatic and has acute primary infection. HIV infected individuals in Category B suffers from Bacillary angiomatosis, Listeriosis, Peripheral neuropathy. Individuals in Category C have Cervical cancer, Encephalopathy, Mycobacterium tuberculosis, Wasting syndrome due to HIV.