T cells (T lymphocytes)
* Types: There are many types of T cells, each with a specialized role. Some key ones include:
* Helper T cells (Th cells): These cells act as "directors" of the immune response. They activate other immune cells, like B cells and cytotoxic T cells, to fight the infection.
* Cytotoxic T cells (Tc cells): These cells directly kill infected cells by releasing toxins or triggering apoptosis (programmed cell death).
* Memory T cells: These cells remember past infections and allow for a faster and stronger response if the same pathogen is encountered again.
* Function: T cells are primarily involved in cell-mediated immunity, meaning they directly target and attack infected cells. They recognize antigens (foreign molecules) presented on the surface of infected cells.
B cells (B lymphocytes)
* Function: B cells are responsible for humoral immunity, which involves producing antibodies.
* Antibody Production: When a B cell encounters an antigen, it differentiates into a plasma cell. Plasma cells produce and release antibodies that can bind to the antigen, neutralizing it and marking it for destruction by other immune cells.
* Memory B cells: Like T cells, B cells also form memory cells that remember past infections and allow for a faster antibody response upon re-exposure.
Working Together:
T cells and B cells work together in a complex and orchestrated way to fight off infections:
1. Antigen Presentation: Antigen-presenting cells (APCs), like macrophages and dendritic cells, engulf pathogens and display fragments of the pathogen's antigens on their surface.
2. T cell Activation: Helper T cells recognize these antigens presented by APCs and become activated.
3. B cell Activation: Helper T cells release signals that activate B cells that are specific for the same antigen.
4. Antibody Production: Activated B cells differentiate into plasma cells and produce antibodies.
5. Target Elimination: Antibodies bind to antigens, neutralizing the pathogen and marking it for destruction by other immune cells (like macrophages and neutrophils). Cytotoxic T cells also directly kill infected cells.
In summary, T cells and B cells are essential parts of the adaptive immune system, responsible for recognizing specific pathogens, triggering immune responses, and providing long-lasting immunity. They work together to eliminate threats to the body and protect us from disease.
