In a nutshell…

the HIV virus continuously changes the antigens on its surface. the immune system creates antibodies for one form, but by the time they are ready the virus has already changed. This way the immune system is "exhausted", and the ability to produce antibodies progressively decreases.

Following up on the last entry, the "escape mutants" (they’re really called that) that the host has no antibodies for are attacking important coordinating cells of the immune system – if they can decimate the system before new antibodies are made, response to the new antibodies can’t happen.

oh yeah, i forgot to mention that… infection of T4 cells…

yup, majorly they infect CD4 T-cells which I consider as ‘the root’ of the immune system…

Also, the AIDS virus attacks regular stomatic cells, body cells, so the immune system does not know which cells to attack. And the infected host cells do not develop correctly and are imatue and cannot perform their function.

i don’t understand your post(i am not saying it is incorrect). but you made a typo, which resulted into stomatic cells(plant cells, instead of the animal "somatic cells").

Until now nobody knows how HIV actually works in human body,I once saw a graph of(number of HIV in blood of patient vs years)showing that the number of HIV increases in the first year then it drops and stays stable for five years.After five years the concentration of HIV raises gradually until the patient dies.Why does the number of HIV decrease for five years???!

As I understand it, the immune system actually does a good job of controlling the infection for quite a while. Over time, the viruses continue to produce mutants (their copying is error-prone). Significantly changed viruses are likely to be bad at their job and/or still caught by antibodies; although the odds of a mutant being functionally infective but invisible to current antibodies are great, after many many thousand generations, they actually become likely. The escape mutants take a somewhat compromised immune system and, before antibodies to these new viruses can be made, cut its effectiveness way down – HIV-positive progresses to AIDS.