Editing Immunology (section)

== 2. The Adaptive Immune System: Specificity and Memory ==

If an infection outpaces the innate system, the adaptive immune system is activated. This branch takes days to weeks to mount a full response, but it is exquisitely specific to the exact pathogen. Crucially, it creates immunological memory, allowing for a much faster and stronger response if the same pathogen is encountered again.

=== T Lymphocytes (Cell-Mediated Immunity) ===
T cells mature in the thymus and are responsible for directing the broader immune response and destroying infected cells.
* '''Helper T Cells (CD4+):''' Act as the commanders of the adaptive response. When they are presented with a specific antigen by innate immune cells, they release signaling molecules that activate both other T cells and B cells.
* '''Cytotoxic T Cells (CD8+):''' Actively seek out and induce apoptosis (programmed cell death) in the body's own cells that have become infected with viruses or have turned cancerous.

=== B Lymphocytes and Antibody Production (Humoral Immunity) ===
B cells mature in the bone marrow. Their primary function is to produce antibodies—large, Y-shaped proteins that circulate in the blood and lymphatic fluid.
* '''Clonal Expansion:''' When a B cell's specific receptor perfectly matches an invading antigen (often requiring secondary confirmation from a Helper T cell), the B cell begins to divide rapidly.
* '''Plasma Cells:''' These cloned B cells differentiate into plasma cells, which act as biological factories, secreting thousands of antibodies per second.
* '''Neutralization and Opsonization:''' Antibodies bind specifically to the pathogen, either neutralizing it directly (e.g., blocking a virus from entering a cell) or "tagging" it (a process called opsonization), making it highly visible and appetizing for innate phagocytes to clear.