What steps happen when a lymphocyte recognizes pathogen?
When a lymphocyte recognizes a pathogen, a series of steps occur to initiate an immune response. Here is a general overview of these steps:
Recognition: Lymphocytes, specifically B cells and T cells, have receptors on their cell surfaces that can recognize specific antigens or foreign molecules associated with pathogens. These receptors, known as B cell receptors (BCRs) and T cell receptors (TCRs), bind to the antigens and trigger the activation of the lymphocyte.
Antigen presentation: For T cells to recognize antigens, they need to be presented in a specific way by antigen-presenting cells (APCs). APCs, such as macrophages and dendritic cells, engulf and process pathogens or infected cells, breaking them down into smaller fragments. These fragments, or antigens, are then displayed on the APC's cell surface bound to major histocompatibility complex (MHC) molecules.
T cell activation: Helper T cells, a type of T cell, play a crucial role in activating other immune cells. When a helper T cell's TCR binds to a specific antigen presented on an MHC molecule of an APC, it becomes activated. This activation involves the release of cytokines, small proteins that act as messengers, and the expression of certain surface proteins.
B cell activation: Activated helper T cells can then interact with B cells that have bound to the same antigen with their BCRs. This interaction, along with additional signals provided by the T cells, leads to the activation of the B cells. Activated B cells proliferate, differentiate into plasma cells, and begin to secrete large amounts of antibodies.
Antibody production: Plasma cells, which are differentiated B cells, produce and release antibodies specific to the recognized antigen. These antibodies bind to the pathogen or its antigens, marking them for destruction by other components of the immune system.
Immune response: The production of antibodies and the activation of other immune cells, such as cytotoxic T cells and phagocytic cells, contribute to the overall immune response against the pathogen. Antibodies can neutralize pathogens, prevent their entry into host cells, or facilitate their destruction by immune cells.
These steps collectively enable the immune system to recognize specific pathogens, mount an appropriate immune response, and eliminate the infection.