The activation of immune cells involves a series of complex processes that are initiated when the immune system detects a pathogen. This process can be divided into several steps:
1. Antigen Recognition: Immune cells recognize foreign antigens through specific receptors. For example, B cells have B cell receptors (BCRs) that bind to specific antigens, while T cells have T cell receptors (TCRs) that recognize antigen fragments presented by Major Histocompatibility Complex (MHC) molecules on the surface of antigen-presenting cells (APCs).
2. Signal Transduction: Binding of the antigen to the receptor triggers a cascade of intracellular signaling pathways. This often involves phosphorylation events and activation of various kinases, leading to changes in gene expression.
3. Proliferation and Differentiation: Activated immune cells undergo clonal expansion and differentiation. For example, activated T cells can differentiate into various subsets such as helper T cells (Th cells) or cytotoxic T cells (Tc cells), each with specific functions in the immune response.
4. Effector Functions: The differentiated immune cells carry out their effector functions. B cells produce antibodies, while T cells can directly kill infected cells or help activate other immune cells. Macrophages and dendritic cells can engulf and digest pathogens, presenting antigens to T cells to further amplify the immune response.
