Potent combination HIV therapy (commonly called ART or HAART) can significantly prolong life. In high-income countries such as Canada, Australia and the U.S. and regions such as Western Europe, doctors increasingly estimate that young adults diagnosed today and who begin ART shortly thereafter and who take their medicines every day exactly as directed and who have minimal co-existing health conditions have a good chance of living into their 70s.
Scientists in the U.S. have collaborated on a project to study how well ART penetrates the body. They have found that while ART is good at getting into cells in the blood and greatly reduces production of HIV in the blood, HIV-infected cells continue to make viruses deep inside the body. This particularly happens in parts of the immune system called lymph nodes and lymphatic tissues. These findings have many potential implications for the future of HIV therapy and for attempts to try to cure HIV infection. In this CATIE News bulletin, we first give a brief explanation of the immune system and some terms that we will use before detailing the recent U.S. findings.
Cells and systems
One group of cells that helps to fight infections is called lymphocytes. These cells can be divided into two groups as follows:
- T-cells (or T-lymphocytes) – these can help organize the immune response to infection; some T-cells can directly attack infected cells and tumours
- B-cells (or B-lymphocytes) – these make antibodies that can help fight some infections
Some T-cells have a receptor called CD4 and we commonly call these cells CD4+ cells. Other T-cells have another receptor called CD8 and we commonly call these cells CD8+ cells.
Deep within the body
The immune system is distributed throughout the body and only a small fraction of its cells (between 2% and 5%) are in the blood at any time. Most T-cells and most of the immune system’s cells are found in places such as the following:
- lymph nodes – locations include the neck, under the arms, in the groin
- lymphatic (or lymphoid) tissue – small extensions of the immune system found around the gut, lungs, mouth, throat (tonsils), sinuses in the nasal passages and ano-genital tract. Germs enter the body through these parts of the body and can be intercepted by cells of the immune system.
- organs – for example, the bone marrow makes all of the immune system’s cells, the thymus gland makes hormones and helps to turn immature cells into T-cells, the spleen filters the blood for germs
Where things happen
Lymph nodes and lymphatic tissue are busy sites of activity. Cells of the immune system bring germs there to be broken down and analysed. Lymph nodes and tissues contain many immune cells; when alerted to the presence of germs, these cells multiply and travel throughout the body to contain infections.