> See also: # Lymphocytes Lymphocytes are [[Blood Cells|white blood cells]] whose primary function is to assist in the [[Adaptive Immunity|adaptive immune response]]. All [[Blood Cells|blood cells]] originate from **hematopoiesis** (differentiation from stem cells within bone marrow). Maturation occurs in the primary lymphoid tissue while activation occurs in the secondary lymphoid tissue ![[Lymphoid Cells of the Immune System.png|400]] ## Lymphocyte Diversity The **most prominent** lymphocytes are [[T-Cells]] and [[B Cells]]. [[T-Cells]] and [[B Cells]] are **morphologically indistinguishable**. - This means that it is *impossible to tell what type of cell they are by appearance alone* (though [[Cellular Staining]] for example). These cells go through three main stages throughout their life: 1. Development 2. Maturation 3. Activation ### Naïve vs Effector Lymphocytes A lymphocyte is called **naive** if it has not yet been activated - [[T-Cell Activation|T-Cells are activated]] inside a [[Lymphoid Organs|lymph node]] when a complementary [[Antibodies|antigen]] is presented to it. Once a lymphocyte has been activated, it becomes capable of performing it's main functions and is called an **effector** cell Both T-Cells and B-Cells can be activated in secondary lymphoid tissue (lymph nodes) although they develop and mature separately ### Innate Lymphoid Cells (ILCs) You can kinda just look at the name to recognize how ILCs differ from B/T-Cells; while they develop antigen-specific receptors to adapt to specific pathogens, ILCs do not. ILCs can be activated by opsonized ## Lymphocyte Behavior ### Clonal Selection & Expansion ![[Pasted image 20231125213743.png]] selection of a single specific B cell by specific antigen, followed by expansion into numerous clone cells with the same specificity ### Lymphocyte Homing Because cells lack any true intelligence (at least the same way our brains work) they must rely purely on [[Cellular Interactions|chemical mediators]] to be directed to where they need to be within the body. One of the more complicated