HIV and AIDS are two differet things : a good education about it is necessary
Human immunodeficiency virus ( HIV ), is a retrovirus that causes the acquired immunodeficiency syndrome ( AIDS , a condition in which the immune system begins to fail, leading to opportunistic infections that get more and more severe throughout the disease's developement, till when the host dies).
Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these body fluids, HIV is present in two different ways:
It is possible to find HIV in the saliva , tears, and urine of infected individuals, but there are no recorded cases of infection by these secretions, and the risk of infection is minimal.
The three major routes of transmission are:
- unprotected sexual intercourse;
- contaminated needles;
- transmission from an infected mother to her baby at birth, or through breast milk.
Screening of blood products for HIV in the developed world has largely eliminated transmission through blood transfusions or infected blood products in these countries.
HIV primarily infects vital cells in the human immune system such as helper T cells (specifically CD4 T cells), macrophages and dendritic cells.
HIV infection leads to low levels of CD4+ T cells through three main mechanisms:
* direct viral killing of infected cells;
* increased rates of apoptosis in infected cells;
* killing of infected CD4+ T cells by CD8 cytotoxic lymphocytes that recognize infected cells.
When CD4+ T cell numbers decline below a critical level, cell-mediated immunity is lost, and the body becomes progressively more susceptible to opportunistic infections.
HIV is different in structure from other retroviruses. It is around 120 nm in diameter (60 times smaller than a red blood cell) and roughly spherical.
HIV genome is composed of two copies of single stranded RNA, enclosed by a conical capsid.
This is in turn surrounded by a plasma membrane of host-cell origin. The single strand RNA is tightly bound to the nucleocapsid proteins p7 and enzymes that are indispensable for the development of the virion, such as reverse transcriptase and integrase.
The nucleocapsid associates with the genomic RNA (one molecule per hexamer) and protects the RNA from digestion by nucleases.
A matrix composed of an association of the viral protein p17 surrounds the capsid, ensuring the integrity of the virion particle.
The envelope is formed when the capsid buds from the host cell, taking some of the host-cell membrane with it.
The envelope includes the glycoproteins gp120 and gp41.
Hiv, cellule T e proliferazione omeostatica
L'Hiv persiste in un reservoir di linfociti T Cd4+ con infezione latente nei soggetti trattati con terapia HAART. Esso persiste prevalentemente nelle cellule T(CM) nei soggetti che presentano la ricostituzione del compartimento CD4+ dopo la terapia: si tratta di un reservoir che viene mantenuto tramite la sopravvivenza delle cellule T e la proliferazione di basso livello guidata dagli antigeni, tendendo a scomparire lentamente nel tempo. Nelle cellule T™ invece si rileva preferenzialmente il DNA provirale nei soggetti aviremici con una bassa conta CD4+ e maggiori livelli di proliferazione omeostatica IL-7-mediata, un meccanismo che assicura la persistenza di queste cellule. Tutto ciò suggerisce che sarebbe possibile ottenere l'eradicazione virale tramite l'uso combinato di interventi strategici mirati contro la replicazione virale e, come accade nei tumori, farmaci che interferiscano con il rinnovamento e la persistenza di cellule T della memoria proliferanti. (Nat Med online 2009, pubblicato il 21/6)
