The Human Immunodeficiency Virus, affects the immune system by using T-helper cells as hosts.
Viruses are extremely small and lack the organelles that are needed for cell replication, such as ribosomes and the necessary enzymes. This is why they need to attach to host cells and use their machineries and resources to increase in numbers.
As seen in the featured image HIV has a spherical structure. The genetic material is protected in the core by a coating of capsid, in the core reverse transcriptase is also found, which is needed for virus replication. The capsid is then surrounded by an envelope and sticking out of it HIV has a large number of attachment proteins that will aid the virus to bind to the host helper T-cell.
HIV replication can only occur when the virus is inside the T-helper cell.
• Attachment proteins attach to receptor molecules on cell membrane of helper T-cell
• Capsid released in T-helper cell, here it breaks down and releases genetic material in cytosol.
• Reverse transcriptase used to make complementary DNA strand from viral RNA template.
• Double stranded DNA made and inserted in human DNA.
• Viral proteins made from viral DNA in human using host cell enzymes.
• Viral proteins assembled into copies of the virus.
The HIV will then spread infecting more of the host’s cells. It does this by budding, the viruses pinch out the T-helper cell and steal some of its cell surface membrane, which then use as envelope; or by lysis, break opening the T-helper cell, causing its death. The latter will lead to the number of helper T-cells to decrease, weakening the immune system. As the viral infection progresses, the number of helper T-cells count will drop below a certain level (this is different for each individual) which begins the immune system to fail gradually, the patient now has AIDS. With AIDS, the immune response is no longer suitable to protect our body against pathogens and patients can develop serious infections which can even be caused by opportunistic diseases, such as the common cold.
At the moment, there is no cure for HIV. Antibiotics only target bacterial enzymes and ribosomes, affecting interfering with their metabolic reactions; however viruses use human enzymes and ribosomes, and antibiotics do not target human processes. The progression of HIV infection to AIDS can be slowed down using antiviral drugs, which are designed to target virus-specific enzymes, such as reverse transcriptase. 
Even if there is yet no vaccine or cure for the virus, there is a small chance that humans with HIV naturally develop broadly neutralising antibodies (bNAbs), but this only happens after about two years from the infection, which means that the virus has already mutated. In recent studies by researchers at the Texas A&M University, it has been found that cattle injected with HIV proteins developed immune response (by producing bNAbs) in just 35 to 50 days. In this short period, the HIV does not have time to change form, so the antibodies are still effective against the it and the infection can be stopped.
It has been theorised that cows potent immune system can be traced back to their extensive gastrointestinal system composed of multi-chambered stomachs. Their stomachs are populated with and incredible number of bacteria, which aid the digestion of grass, but also increase the risk of infections. Therefore, researchers could use this fact to strengthen the human immune system or try to develop vaccines modifying the cattle antibodies in order to treat HIV. 
 CGP Biology