WHAT IS HIV-1?

HIV-1 is one of the most rapidly mutating viruses ever encountered.   Thus there are many different strains of HIV-1.  These strains are all similar, however.  All are a specific type of RNA virus (a virus containing RNA as opposed to DNA) known as a retrovirus.  To enter a cell,  viruses must recognize (bind to) certain proteins encoded by host genes and displayed on the cell surface.   These proteins normally act as receptors for other host molecules, but a virus can also make use of  them.  A virus will bind to these receptors, employing them as entryways into a cell.  Once inside a cell, retroviruses insert their genes into a host's chromosomes.  A retrovirus' genetic material replicates in an unusual way: when a virus enters a cell, a viral enzyme (reverse transcriptase) transcribes viral RNA into duplex DNA.  The cell's machinery then replicates and transcribes this DNA as if it were its own.  Retroviruses thereby ensure that viral genes-which can direct the synthesis of an endless supply of viral particles- are passed to each new generation of cells whenever the initial host cell replicates.  In order to accomplish this feat, retroviruses must obtain the help of several cellular enzymes to splice viral genes into chromosomes and to evade the host's defenses.

HOW HIV-1 EFFECTS THE BODY

HIV-1 primarily attacks immune cells, specifically macrophages and T-cells, which bear the CD4 protein. Without these specific cells, no immune response can be initiated. The CD4 protein typically participates in signaling between the various immune cells.  However, when HIV-1 approaches the cell, CD4 binds to a sugary protein (gp120) protruding from HIV-1. However, CD4 binding alone is insufficient. The cell must also display a second receptor, at least one more protein which the virus may utilize to fuse with the host cell.

M-tropic Phase

Initially the virus is M-tropic: it favors macrophages (large cells of the immune system which engulf and digest cellular debris and invading bacteria).  HIV-1 does not destroy macrophages.  Instead, it finds a safe haven in them while it continues to replicate.

T-tropic Phase

Eventually the virus mutates and favors T-cells (a type of lymphocyte involved in cell-mediated immunity and interactions with other immune cells) over macrophages.  T-tropic viruses readily destroy infected T-cells and thereby contribute to the collapse of the immune system and the onset of AIDS.

Dual-tropic Phase

Between the M-tropic and T-tropic phases, the virus may infect both macrophages and T-cells.  It is therefore "dual-tropic".

Once exposed to the virus, it usually takes 2 weeks to 6 months to develop antibodies (which are substances produced in the blood to fight against invading disease organisms).  There are two blood tests commonly available that will determine if a person has antibodies for HIV-1.  Though a  positive test result means that a person has been infected with the virus, it doesn't mean that the person has or ever will develop AIDS, although 90% will.  Once infected, the person can remain healthy, develop some symptoms, or develop the full disease known as AIDS.  It may take years between first being infected with the virus and the development of AIDS.   Some people may be infected with the AIDS virus and not know it until symptoms develop.  Persons with the virus can transmit it to others although they have no symptoms of the disease.

Symptoms and Transmission