Policing what goes in and out of the body, the immune system is a line of defense guarding against infection whilst distinguishing foreign bodies from the person’s healthy tissue. One of the major components of the immune system is white blood cells, that include B-cells, T-cells or natural killer cells. These cells travel in a person’s blood and tissues looking for foreign bodies such as bacteria, viruses, and parasites to launch an immune attack against. Thus white blood cells are a crucial defense against disease and infection. Now, a study from researchers at Trinity College identifies a previously unknown human immune cell with novel hybrid properties. The team states the newly discovered cells play a key protective role against infection, however, when left unregulated, they can cause tissue damage and autoimmune disease. The study is published in the Journal of Experimental Medicine.
Previous studies show the immune system contains various white cells including T cells recognize and bind antigens on the surface of invading microbes. Molecules called T cell receptors (TCRs) allow T cells to recognize infectious agents with high specificity, these receptors stop T cells attacking and damaging the body’s tissues, and causing autoimmune diseases. At this present time, there are only two recognized populations of T cells expressing either ‘αβ’ or ‘γδ’ TCRs, respectively. The γδ T cells are more commonly found in tissue as opposed to blood and share the characteristics of helper T cells, cytotoxic T cells, and natural killer cells. Whereas αβ TCRs, on the other hand, are found on conventional CD4+ and CD8+ T cells. The current study identifies a new immune cell type expressing both αβ and γδ TCRs.
The current study identifies a new type of white blood cell in mice and humans possessing the characteristics of both αβ and γδ T cells. These hybrid T cells were observed in the thymus of a fetal mouse on the sixteenth day of development, where they undergo differentiation from thymocytes into mature T cell lymphocytes. Results show these cells rapidly respond to Staphylococcus aureus infection and play a key role in quickly eliminating the bacteria from the body. Data findings show although these T cells work to clear microbes, they are also a major causal element of autoimmune disease in the central nervous system.
The lab states the hybrid αβ-γδ T cells work via an inflammatory phenotype primed for chemokine receptors and homing molecules possessing the ability to facilitate migration to sites of inflammation. When the sites are reached the hybrid cells license a subset of encephalitis-causing CD4 T cells, known as T helper 17 cells, to aid in the development of autoimmune disease. They go on to add the hybrid T cells’ ability to trigger an inflammatory cascade could be inhibited in susceptible individuals, providing new targets in the treatment of autoimmune diseases such as psoriasis and multiple sclerosis.
The team surmises they have discovered a previously unknown T cell possessing both αβ and γδ TCRs present in mice and humans. For the future, the researchers state the new discovery will help in the fight against superbugs, and in the development of new therapies for autoimmune diseases, such as multiple sclerosis or rheumatoid arthritis.
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