The adaptive immune system is brilliantly designed to defend us from any type of pathogen through combinations of cell types, T-cells, B-cells, Natural Killers cells, all working together to deliver the right response to battle any pathogen. However as we know the immune system can cause problems to us, the host, such as Type 1 Diabetes caused by destruction of the beta cells in the Islet of Langerhans or ugly skin diseases like atopic dermatitis. Leaving the science community pondering how does the immune system know when to stop?
One cell type known to prevent the immune system from causing problems is the regulatory T-cell or Treg. People who have a general understanding of the immune system typically know of the T-helper cell. The Th cell is attacked by the HIV virus via the CD4 protein expressed on the cell surface and is responsible for activating a B-cell to initiate the correct antibody response. There is also the cytotoxic T-cell which are responsible for eliminating any virus infected cell within the body expressing a CD8 cell surface protein.
What is T-cell (T-Regulatory Cells)
We know blood cells both white and red are generated in the bone marrow from progenitor cells, however premature T-cell travel from the bone marrow to the thymus where they maturate. The selection process involves the ability to initiate an immune response, but not recognize host cells. In the thymus is where some T-cells can slip through the cracks by mistakenly being able to initiate attacks on host cells. The thymus release ‘Naive T-cells’ which move to various lymph nodes in the body, and these cells typically present both the CD4 and CD8 cell surface proteins. If they differentiate into helper T-cells they will only present CD4 proteins or if cytotoxic T-cells are generated only the CD8 marker is present. Innate immune cells such as macrophage and dendritic cells are important to the development of the T-cell because they present broken pieces of pathogenic protein to the T-cell while secreting cytokines that aid in their development to fight off the specific pathogen. This is where the T-regulatory cells can be developed and their CD25 cell surface marker is up regulated.
The importance of these cells is to down regulate other T-cell responses and effectively end an immune response after it has begun. So the important factor among the T-cell immune response is time. Initially it would be not be beneficial to generate excess Treg cells as they would halt the immune response before it becomes effective enough to stop infection. Similarly Treg expression would need to be grow near the end of the response to stop the body from generating too strong of a response. This cell is under a lot of study over the past few years and will be continued to be studied. I have linked here interesting papers and videos that explain the function and expression of this cell in more detail.
Resources and Helpful Links for T-Regulatory Cells
T-regulatory cells in suppressing immune response.