Lymphocytes Flashcards
Lymphocyte definition
A subtype of white blood cell
four different types of lymphocyte
B cell, T cell, natural killer cell, small lymphocyte
stages of development of lymphocytes
- stem cells differentiate in bone marrow
- all lymphocytes originate from a common lymphoid progenitor
- B cells mature into B lymphocytes in the Peyer’s patches of the intestine
- T cells migrate to and mature in a distinct organ called the thymus
What are the Peyer’s patches?
Organised lymphoid follicles, found in the distal jejunum and ileum
Characterised by the follicle- associated epithelium
Function of Peyer’s patches
trap foreign particles, surveil them and destroy them. Lymphocytes and antigens meet here ( and the lymph nodes), not the blood
Structure of Peyer’s patches
covered in special follicle associated epithelium that contains special microfold cells- sample antigen directly from the lumen and deliver it to APS cells
APS cells located in a pocket structure on the basolateral side
Development of T cells explained
- originate from haematopoietic stem cells which reside in the bone marrow
- HSC then differentiate into mutipotent progenitors- myeloid and lymphoid
- lymphoid cells then differentiate into T, B or NK cells- called common lymphoid progenitors
Secondary lymphoid organ definition
location for antigens to encounter lymphocytes. Region where the lymphocytes proliferate
examples of secondary lymphoid organ
lymph nodes, spleen and Peyer’s patches
How do all the lymphocytes connect the dispersed lymph tissue?
leave blood at special endothelium, only on certain venules within lymph nodes, tonsils and other lymphoid organs
primary lymphoid organ definition
lymphatic regions where the lymphocytes mature- thymus and bone marrow
Two main types of T cell
helper T cell and killer T cell
What differs between them?
cytotoxic T cell have a CD8 antigen receptor, whereas helper T cells have a CD4 receptor
Helper T cell function
Play a role in adaptive immunity
Release T cell cytokines that stimulate killer cells
Bind to antigens found on antigen presenting cells, Th cell then binds and lead to the release of cytokines
Cytokines definition
small proteins that are important in cell signalling
Cytotoxic T cell function
immune surveillance
patrols body for ‘missing self’ absence of cell surface ‘passport’ molecules
CD8 receptors bind to specific antigens
Kills cancer cells, cells that are infected by a pathogen or that are damaged in another way
How do killer T cells induce destruction?
Release cytotoxins, such as perforin, granzymes and granulysin- target cell that causes a caspase cascade that leads to apoptosis
What are MHC molecules?
surface proteins essential for the acquired immune system to recognise antigens
MHC molecule functions
bind to antigens and present them on their surface for recognition
Relationship between MHC, Th and Tc
As a lineage of leukocytes, lymphocytes reside in peripheral lymphoid tissues, including lymphoid follicles and lymph nodes, and include B cells, T cells, and natural killer cells (NK cells). B cells, which act specifically, secrete antibody molecules, but do not bind MHC. T cells, which act specifically, as well as NK cells, which act innately, interact with MHC. NK cells express Killer Ig-like receptors (KIRs) that bind to MHC I molecules and signal through ITIM (immunoreceptor tyrosine inhibition motif) recruitment and activation of protein tyrosine phosphatases. This means in contrast to CD8/TCR interaction that activates Tc lymphocytes, NK cells become deactivated when bound to MHC I. When MHC class I expression is low, as is typically the case with abnormal cell function during viral infection or tumourigenesis, NK cells lose the inhibitory KIR signal and trigger programmed cell death of the abnormal cell. NK cells thus help prevent progress of cancerous cells by contributing to tumor surveillance.
B cell function
Humoral immunity component of the adaptive immune system- secrete antibodies
Can become antigen presenting cells and secrete cytokines
What happens if an early B cell binds to a self antigen?
clonal deletion, receptor editing, anergy or ignorance
What does this result in?
State of central tolerance- mature b cells don’t bind to self antigens in bone arrow
Where do the B cells move after the bone marrow?
Migrate into the spleen, transition from T1 to T2 B cells
