T cells are special white blood cells that help fight off sickness. Your immune system has two ways of fighting sickness: one is a general response, and the other is a specific response. T cells are part of the specific response, which is also called T cell immunity. They start in your bone marrow and finish growing in a small organ called the thymus, which is found in between your lungs. There are four types of T cells, each with their own job. Let's take a closer look at each type. T cell immunity is an important part of your body's defense against illness.

T lymphocytes are also known as T cells!

To fight off sickness, T cells are divided into four types. Each type has a special job to do. These are:

1. Helper T cells
2. Cytotoxic T cells
3. Regulatory T cells
4. Memory T cells

Helper T lymphocytes

Helper T cells and B cells work together to fight off sickness. Helper T cells make cytokines that tell B cells to make antibodies to fight the sickness. Cytokines are special proteins that help the immune system work. Antibodies are also proteins made by B cells that help rid of sickness by attacking and neutralizing the pathogens causing the sickness.

Cytotoxic T lymphocytes

Killer T cells, also known as cytotoxic T cells, directly fight off sickness by releasing perforin and granzymes. Perforin makes holes in the cell membranes of the pathogens, granzymes to enter and cause apoptosis, which destroys the pathogen and cells. This process does not cause inflammation.

ytotoxic T cells also make a cytokine called IFN-γ, which stops the virus from replicating and activates macrophages to help clear viral infections. These cells are called CD8+ T cells because they have a glycoprotein called CD8 on their surface, which lets them bind to antigens on infected cells.

Regulatory T lymphocytes

Regulatory T cells have a crucial role in preventing the immune system from overreacting. They help to suppress the continuous activation of helper and cytotoxic T cells and limits their reaction after clearing the pathogen.

Without proper regulation, the immune response can lead to autoimmune diseases, where the immune system attacks the body's tissues, and allergies, which occur when the immune system reacts to harmless antigens. Regulatory T cells are essential in preventing these types of immune disorders.

Memory T lymphocytes

Memory T cells play a crucial role in the secondary immune response, which is the rapid response to antigens after initial exposure. These long-lived cells reside in the bloodstream for an extended period and differentiate rapidly into helper and cytotoxic T lymphocytes when they detect the presence of the antigen they are complementary to, helping to clear the pathogen.

The primary immune response occurs during the initial exposure to a new antigen, such as when someone is first infected with the chickenpox virus. This response is generally slow, but memory T and B lymphocytes are formed during this time. If the person is exposed to the virus again, the secondary immune response is activated, and the memory T and B lymphocytes are quickly differentiated into different effector cells, leading to a more rapid and effective response compared to the primary immune response.

T lymphocytes in cell-mediated immunity

Cell-mediated immunity is an immune response that doesn't involve antibodies. Instead, mature T cells, macrophages, and cytokines are used to fight. T cells can recognise cells that have been infected and modified by a pathogen by detecting antigens presented on the surface of antigen-presenting cells (APCs), such as infected cells presenting pathogenic antigens on their major histocompatibility complex (MHC).

The stages involved in cell-mediated immunity involving T lymphocytes are:

1. A pathogen invades the body.
2. Phagocytes engulf the pathogen and present the antigen on the surface of their plasma membrane.
3. Receptors on the surface of helper T lymphocytes detect and fit the antigen.
4. The helper T lymphocytes bind to the antigen and become activated, secreting cytokines to differentiate into cytotoxic T lymphocytes, memory T lymphocytes, and regulatory T lymphocytes, as well as stimulating phagocytosis.
5. Helper T lymphocytes can also activate B lymphocytes, but they are a part of humoral immunity.

The three primary phagocytic cells involved in cell-mediated immunity are macrophages, neutrophils, and dendritic cells.

Differences between cell-mediated immunity and humoral immunity

The adaptive immune response consists of both cell-mediated immunity and humoral immunity. Cell-mediated immunity involves T lymphocytes and macrophages and responds to cells that have been modified by engulfed pathogens. On the other hand, humoral immunity involves B lymphocytes and responds to extracellular pathogens. While cell-mediated immunity doesn't involve the production of antigen-specific antibodies, humoral immunity does.

There are four types of T lymphocytes involved in cell-mediated immunity: helper, cytotoxic, regulatory, and memory T lymphocytes. Helper T lymphocytes stimulate other cells by secreting cytokines. Cytotoxic T lymphocytes destroy infected cells by releasing perforin and granzymes. Regulatory T lymphocytes suppress the immune system, and memory T lymphocytes contribute to the secondary immune response. In summary, while cell-mediated immunity differs from humoral immunity, both are critical components of the adaptive immune response.

T Cell Immunity

What are T lymphocytes responsible for?

T lymphocytes are responsible for the cell-mediated immune response. This involves the response against cells that have been modified due to infection. 

How are T lymphocytes involved in the adaptive immune response?

They are involved because they target specific antigens directly. 

What is cell-mediated immunity?

Cell-mediated immunity is an immune response that detects cells that have been modified by a pathogen. For example, immune cells that have phagocytosed and processed a virus will present viral antigens on their plasma membrane (on their MHC). These cells are detected by T lymphocytes.

What are the roles of T lymphocytes during the primary immune response?

The primary immune response describes the initial exposure to a new antigen. T lymphocytes become activated when they bind to APC's (these present antigens on their surface) and this stimulates their differentiation into helper, cytotoxic, regulatory and memory T lymphocytes. They will also activate B lymphocytes by secreting cytokines.

‍