Virtual memory T cells (T
VM) are a subtype of
T lymphocytes. These are cells that have a memory
phenotype
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...
but have not been exposed to a foreign
antigen
In immunology, an antigen (Ag) is a molecule or molecular structure or any foreign particulate matter or a pollen grain that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...
. They are classified as memory cells but do not have an obvious memory function. They were first observed and described in 2009.
The name comes from a computerized "
virtual memory
In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...
" that describes a working memory based on an alternative use of an existing space.
Origin of TVM
arise from autoreactive T cells during the
thymus
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...
section. Autoreactive lymphocytes are commonly removed in the thymus because they recognize the body's own structure and could induce autoimmune disease. However, some autoreactive
CD8+ T cells are intended for development into T
VM. This process is controlled by CD8-
Lck. The generation and maintenance of the TVM population depends on the transcription factors Eomes and
IRF4, type I interfering signaling. The presence of the
IL-15 cytokine is then essential.
Function of virtual memory T-lymphocytes
The existence of memory T cells is also known in non-immunized animals. T
VM are cells specific and reactive to foreign antigens that have never met. There are different phenotypic mismatches between naive, true memory and T
VM. We can find functional differences after activation. It is easy to distinguish naive cells from memory, but true memory from T
VM can only be distinguished by
CD49d and
CD122
Interleukin-2 receptor subunit beta is a protein that in humans is encoded by the ''IL2RB'' gene. Also known as CD122; IL15RB; P70-75.
Function
The interleukin 2 receptor, which is involved in T cell-mediated immune responses, is present in 3 ...
markers.
T
VM produce a stronger inflammatory response using
IL-12 and
IL-18 cytokines than naive T cells.
They are a significant producer of
IFN-γ
Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock ...
.
Compared to other naive phenotypes, T
VM represents only 10-30% of the population, but outperforms other types of subpopulation with its stronger proliferation. However, the reaction is slower than true memory cells. These properties suggest that virtual memory T cells may participate in both innate and adaptive immune responses during the immune response.
Another indispensable feature is the suppression of potential states. This occurs already in the development of virtual memory cells from autoreactive T cell clones. For this reason, some scientists thought that TVM could be used in the fight against autoimmunity, but so far no evidence has been found.
The physiological role of virtual memory T lymphocytes has yet to be investigated, but research suggests that they have a unique type of response to pathogens and contribute to the functional diversity of the T cell immune system, which is required for effective immune defense.
CD4 positive TVM
Previous paragraphs dealt with only CD8+ T lymphocytes, but
CD4
In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic ...
+ virtual memory T cells are also described.
The function of these cells is not known, but an even more likely relationship to autoimmune conditions is assumed, whether in their suppression or formation.
References
{{Lymphocytes
T cells