The virus of the human immunodéficience or HIV

HIV (English HIV) is a virus whose genome is in the form of ribonucleic acid (ARN or English RNA). This RNA is contained in a proteinic box or “capsid”, itself surrounded by an envelope. This envelope comes from the cytoplasmic membrane of the infected cell and is presented, for this reason, in the form of a lipidic double-layer. However, this one is roughcast of spicules consisted of two kinds of glycoprotéines, the gp120 and the gp41 (fig. 1).
These glycoprotéines intervenes in the first phases of the multiplication of the virus in the cell. It is by the gp120 that the virus sticks to the cytoplasmic membrane of the cell which it will infect, very precisely on the level of two structures of cellular origin, molecule CD4 and a coreceptor. As for the gp41, it intervenes to amalgamate the virus with the cell. Thus, the viral capsid containing the viral RNA passes inside the cytoplasm (fig. 2 – stage 1).
There, the viral RNA is transcribed in desoxyribonucleic acid (DNA or DNA) (F ig. 2 – stage 2 and fig. 3). This transcription of DNA RNA is the opposite operation of the usual transcription which the cell can make (which transcribes of DNA in RNA to produce the RNA of ribosomes, the RNA messengers and the RNA of transfer). This “opposite” transcription requires an enzyme special, viral, contained in the capsid: the opposite transcriptase (TI) or, in English, reverse transcriptase (RT). The HIV belongs thus to the retroviruses. This operation of opposite transcription is complex and comprises many errors which lead to as many changes in the viral genome. Those modify the structures of the HIV, the antigenic structures target of antiviral immunizing defenses and the enzymes
targets of the antirétroviraux one.
This viral DNA will be closed again on itself, will be transported on the level of the core of the cell and will fit (to be integrated) in cellular DNA, that thanks to a second viral enzyme: the intégrase (fig. 2 – stage 3 and fig. 3). Thus, the viral genome will be part from now on of the cellular genome, and will remain there with the shelter as long as the cell will live, escaping immunizing defenses as with the antirétroviraux treatments.
Starting from the cellular genome, the integrated viral genome will function, with many regards, like a cellular gene: it will be transcribed by the cell itself in viral RNA (F ig. 2 – stage 4), component, ones of new viral genomes, others of the viral messengers translated into new viral proteins (proteins of capsid, enzymes viral, glycoprotéines of envelope gp120 and gp41) (fig. 2 – stage 5).
The assembly of these new viral components (RNA and proteins) will reconstitute a hundred new viruses. With this stage, intervenes a third viral enzyme, the protease, necessary to the cutting of viral proteins (fig. 2 – stage 6). Those are indeed produced in blocks, in the form of giant precursors, which should be cut up (to cleave). There is a stage of “maturation”, necessary so that the new viruses, intended to leave the cell to go to infect others of them, are endowed with infectious capacity (fig. 2 – stage 7).
Thus, the currently available antirétroviraux drugs or in experimentation, aim one of the four following viral structures (fig.2 – framed 1 to 4): the gp41 responsible for the fusion of the virus to the cell, the opposite transcriptase, person in charge of the transcription of the viral viral DNA RNA, the intégrase responsible for the integration of viral DNA in the cellular genome, and the protease responsible for the cleavage of viral proteins at the end of the cycle.
To be effective, the antirétroviraux treatments will have to surmount, among various obstacles, two of a virological nature:
1. changes on the targets of antirétroviraux, leading to resistance to the corresponding drugs, and obliging to modify the composition of the treatment;
the frequency of these changes of resistance is reduced by the use of antirétroviraux in associations;

2. the integration of the viral genome in the cellular genome, from where it cannot be eliminated, so that any stop of the treatment finds it intact and inevitably involves a resumption of the viral multiplication. From where importance of a catch of antirétroviraux regular and to effective amounts, i.e. of a good observance.

THE HIV, IN SHORT
Like all the viruses, the HIV, to reproduce (replication) must imperatively parasitize a cell, here the lymphocytes T CD4.
Four principal times are distinguished:
1. Penetration in the cell, after fusion with the cellular membrane (protein gp 120).
2. Transformation of HIV ARN into HIV DNA thanks to an enzyme (copier), REVERSE TRANSCRIPTASE.
3. Integration of HIV DNA in the DNA of the lymphocyte.
4. The DNA of the lymphocyte is mistaken and manufactures viral proteins it is adire HIV (rôle++ of an enzyme: PROTEASE).
Excretion by the cell of new viruses HIV.