HIV primarily infects CD4+ T cells, a type of white blood cell that coordinates your immune system’s response to infections. But CD4+ T cells aren’t the only targets. HIV also infects macrophages, microglial cells, and astrocytes in the brain, and it exploits dendritic cells to spread through the body. Understanding which cells the virus targets explains why HIV causes such widespread immune damage and why it’s so difficult to eliminate.
CD4+ T Cells: The Primary Target
CD4+ T cells are the main cells HIV seeks out and destroys. These white blood cells act as the immune system’s coordinators, helping your body fight off viruses, bacteria, and fungi. A healthy person has between 500 and 1,500 CD4 cells per cubic millimeter of blood. Left untreated, HIV gradually kills these cells. When the count drops below 200, the immune system is so compromised that it meets the clinical definition of AIDS.
HIV gets inside CD4+ T cells through a specific sequence. The virus carries a surface protein called gp120, which locks onto the CD4 receptor on the cell’s surface like a key fitting a lock. But that initial attachment isn’t enough. The virus also needs to bind to a second receptor, called a co-receptor, before it can fuse with the cell membrane and inject its genetic material inside.
The two main co-receptors are CCR5 and CXCR4. Early in infection, HIV tends to use CCR5 to enter cells. These strains can infect both CD4+ T cells and macrophages. As the disease progresses, some strains evolve to use CXCR4 instead, which gives the virus access to a broader range of CD4+ T cells. Some strains can use either co-receptor. This shift in co-receptor preference is one reason the infection becomes more aggressive over time.
Massive Early Loss in the Gut
One of the most striking discoveries in HIV research is how quickly the virus devastates CD4+ T cells in the intestinal tract. The gut contains a huge concentration of immune cells, and HIV tears through them within days of infection, regardless of how the virus entered the body. This near-total wipeout of gut CD4+ T cells happens long before blood tests show significant declines. It’s a major reason why HIV causes such deep immune damage so early, even before a person feels seriously ill. The gut’s immune lining never fully recovers, even with treatment, and its breakdown allows bacteria to leak into the bloodstream, fueling chronic inflammation.
Macrophages and Monocytes
Macrophages are immune cells that patrol your tissues, swallowing and digesting pathogens. Like CD4+ T cells, they carry the CD4 receptor and the CCR5 co-receptor on their surface, though at lower levels. This makes them vulnerable to infection by CCR5-using strains of HIV.
What makes macrophages especially important is their longevity. Unlike CD4+ T cells, which HIV rapidly kills, macrophages are more resistant to the virus’s destructive effects. They can survive for months or years while harboring the virus inside them. Some tissue-resident macrophages are even capable of self-renewal, meaning they can replenish their own numbers without relying on new cells from the bloodstream. This makes them potential long-term hiding spots for the virus.
In advanced, untreated disease, macrophage infection becomes increasingly significant. As CD4+ T cells are depleted, macrophages become a principal source of new virus in the body. Infected macrophages also drive complications like HIV-associated dementia by producing inflammatory molecules and neurotoxins in the brain. Their reduced susceptibility to some antiretroviral drugs raises concerns that they may harbor low-level viral replication even during treatment.
Dendritic Cells: The Unwitting Couriers
Dendritic cells aren’t a major site of HIV replication, but they play a critical role in spreading the virus. These immune cells sit in mucosal tissues (the lining of the genitals, rectum, and mouth) where they’re among the first cells to encounter HIV during sexual transmission.
Dendritic cells carry a surface protein called DC-SIGN that grabs onto HIV’s outer envelope. Instead of destroying the virus, dendritic cells essentially carry it like cargo. Their normal job is to capture foreign material at body surfaces and transport it to lymph nodes, where they present it to T cells to trigger an immune response. HIV hijacks this process. The dendritic cells ferry the virus straight to lymph nodes packed with CD4+ T cells, delivering it to exactly the cells it needs to infect. This “trans-infection” mechanism turns the body’s own early warning system into a delivery service for the virus.
Brain Cells: Microglia and Astrocytes
HIV crosses into the brain early in infection, and the central nervous system becomes one of the hardest places to reach the virus with treatment. The major targets in the brain are perivascular macrophages (immune cells lining blood vessels in the brain), microglia (the brain’s resident immune cells), and astrocytes.
Astrocytes are particularly noteworthy because they don’t get infected the usual way. They’re largely resistant to free-floating virus. Instead, they become infected through direct cell-to-cell contact, where immature viral particles budding off an infected immune cell bind to co-receptors on the astrocyte’s surface, bypassing the need for the CD4 receptor entirely. Astrocytes are extremely long-lived, turn over very slowly, and don’t die when infected. This makes them an ideal hiding place for the virus. Research has found that the number of infected astrocytes correlates with the severity of neurological damage in people with HIV-related brain disease. Inflammatory signals can also trigger these quietly infected astrocytes to start producing new virus, potentially reseeding the infection even if it’s been cleared from other parts of the body.
The Latent Reservoir in Resting T Cells
Perhaps the biggest obstacle to curing HIV is the latent reservoir: a small pool of infected cells that carry the virus’s genetic code woven into their own DNA but aren’t actively producing new virus. The primary home for this reservoir is resting memory CD4+ T cells.
Here’s how it works. HIV normally infects activated T cells, the ones currently fighting an infection. Occasionally, an infected T cell transitions back into a resting, or “memory,” state before the virus kills it. In this quiet state, the cell’s machinery essentially goes dormant, and the viral DNA integrated into the cell’s genome goes silent along with it. The cell can survive for years or even decades in this state, invisible to both the immune system and antiretroviral drugs.
Resting memory T cells come in several subtypes. Central memory and transitional memory T cells appear to be the major components of this reservoir. Resting T cells have natural barriers to infection, including a rigid internal skeleton that blocks viral transport and low levels of the cellular machinery HIV needs to replicate. Most latent infection likely happens not by direct infection of resting cells, but when already-infected, active T cells settle back into a resting state. If treatment is ever stopped, these silently infected cells can reactivate and begin producing virus again, causing viral levels to rebound. This is why people with HIV need to stay on treatment indefinitely, even when the virus is undetectable in their blood.
Why So Many Cell Types Matter
HIV’s ability to infect multiple cell types across different tissues is what makes it so persistent. CD4+ T cells are where the vast majority of viral replication happens, but macrophages, astrocytes, and resting memory T cells each serve as reservoirs where the virus can hide from drugs and the immune system. The gut loses most of its CD4+ T cells within days. The brain becomes a protected sanctuary behind the blood-brain barrier. Dendritic cells accelerate the spread of infection from the very first exposure. Each of these cell types represents a distinct challenge for treatment and explains why, despite decades of effective antiretroviral therapy, a complete cure remains elusive.