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Different Types of T Cells

October 2020

T Cells

T Cells, or T lymphocytes, are a major part of the immune system. They are cells specifically designed to fight infections they have not yet encountered. As part of any research, there may be a time when you need T cells for isolation. They mature in the thymus until released into the bloodstream as naive T cells. Naive T cells are unassigned T lymphocytes that search for an antigen-presenting cell (APC).

T Cell Activation

When a T cell encounters a recognizable APC, the naïve cell receives a signal to mature. There are three types of signals: TCR, BCR, and cytokine signals. If a cell receives all three signals, it will mature into an effector cell. If a cell only receives one of the signals (TCR or BCR), the cell will become useless.

Effector Cells

Depending on the APC a naive cell comes across it can become an effector T cell. Effector T cells have relatively short lifespans and carry out the functions of an immune response. They can be cytotoxic, helper, and regulatory T cells.

Cytotoxic T Cells

Cytotoxic T Cells, also known as CD8+ cells, have the primary job to kill toxic/target cells. Upon recognition, their purpose becomes the removal of virally infected cells, bacteria, and tumor fragments (such as cancer cells) through a process called apoptosis. Apoptosis occurs when a cell’s internal organelles are destroyed causing it to die from the inside out.

Helper T Cells

T helper cells, or CD4+ cells, are similar to cytotoxic cells but have a wider range of functions. These cells are extremely important to cell immunity because they are required for most adaptive immune responses. T helper cells become activated when presented with antigens and have the ability to differentiate into cell subtypes. When activated, helper T cells multiply and secrete cytokines that summon macrophages and cytotoxic T cells to the infected site.

Regulatory T Cells

The final type of effector cell is the regulatory T cell. Regulatory T cells are tasked with stopping an autoimmune response once the threat has been eliminated. After helper T cells and cytotoxic T cells bind to a pathogen and work together to rid the body of it, they no longer serve a purpose. Regulatory T cells stop them from taking up space or accidentally attacking healthy cells until they succumb to apoptosis.

Memory T Cells

While these three types of effector cells handle the main immune response, they are not the only variations of T cells. Some T lymphocytes are present even after removing a pathogen. These long-living lymphocytes are memory T cells and are highly capable of responding to antigens upon reintroduction.

These cells are formed after an infection and are extremely important because they have the ability to expand into large numbers of effector T cells upon exposure to familiar antigens. Memory cells are unique because they remember pathogens and infectious cells faster than others allowing them to fight off bacteria and viruses quickly. Memory T cells are the reason vaccines can create immunities in the body.

Applications

Each of these T cell variations can help us to learn about diseases and our bodies’ responses to them. Naive T cells teach us about adaptability; effector cells give us ideas for methods of treatment; memory T cells assist us in creating vaccines and medicine. T cells are an essential part of the medical research field and could pave the way to many breakthroughs in the near future.

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