Flashcards in Anatomy and Physiology of the Immune System Deck (13)
What are the two classes of cells in the immune system, and what are their sub-types?
Mononucleated and Polymorphonuclear cells. The mononucleated cells include lymphocytes and monocytes. The polymorphonuclear cells include eosinophils, neutrophils, and basophils.
How did eosinophils, neutrophils, and basophils get their names and what functions do they imply?
Eosinophils stain with a red, acidic dye called Eosin (Eos, goddess of dawn, hence red). B/c it is acidic, it binds to basic proteins, of which the eosinophil has many. These basic proteins allow the eosinophil to kill worms effectively. Neutrophils do not stain well with any dye, hence their "neutral" moniker (neutrally acidic/basic too?)
What is the normal count of WBC in blood, and what is the normal percentage of each cell type?
Total WBC 4,500-10,500 per uL (4.5-10.5X10^9/L) Neutrophils 40-60%, Eosinophils 1-4%, Basophils 0.5-1%, Monocytes 2-8%, Lymphocytes 20-40%
What are the central lymphoid organs?
The central organs are the ones in which the lymphocytes develop. These are the bone marrow and the thymus. (In mammalian embryos, bane marrow function is first found in the yolk sac, and then the liver.)
What are the peripheral lymphoid organs?
The peripheral lymphoid organs are the lymph nodes, spleen, and Peyer's patches. Peyer's patches are found in the gut and mucosa, where GALT/MALT (Gut/mucosa associated lymphoid tissue) exists just deep to the epithelial lining. Broadly speaking, the gut is the largest lymphoid organ in the body.
What is the course of lymph and cells through a lymph node?
Lymph fluid and cells enter through the afferent lymph tubules diffusing through the sub capsular sinus into the cortex. The cortex is arranged in follicles and tightly packed with B cells (10^9 cells/gram). Often, lighter stained areas (germinal centers) are present within the follicles, indicating the rapid cell division of an active immune response. DC cells move through the cortex and generally settle on the border of the cortex and deep(para) cortex, which is tightly packed with T cells. Lymph fluid may then drain out of the node through the efferent lymph tubules located past the medulla in the hilum, along with the associated blood vessels.
How and where do follicular helper T-cells come into play in the immune response inside a lymph node?
Follicular helper cells become activated in the deep cortex of the node and travel to the cortex where they help to activate the associated B cells. This begins the creation of the germinal center.
What is the general process of lymphocyte circulation?
Lymphocytes in the blood enter into nodes through the walls of post-capillary venues, where the endothelial cells are high and cuboidal instead of the usual squamous. These cells also are rich in signaling "hand shaking" molecules that select for the correct WBC and help slow them in the blood stream. All WBC preferentially leave the blood stream at PCV, but the PCV in lymph nodes are particularly suited for high traffic. Lymphocytes in the lymph may move from one node to the next and eventually into the thoracic duct and back into the bloods stream.
Why would a lymphocyte move from one node to another?
Follicular helper T cells may move from one node to another in order to facilitate a broader immune response. As they help stimulate appropriate B cells to divide and produce antigens, the follicular helpers play a critical role in body-wide immune response.
How does the immune system behave in the gut (GALT/MALT)?
In the gut, the immune system is organized in Peyer's patches which are lymph node-like structures immediately deep to the intestinal mucosa. Peyer's patches include specialized mucosal M-cells which ingest proteins and particles as large as viruses, transport them to the abluminal side where DCs ingest them and present them to the T cells of the Peyer's patch. The immune cells must then decide whether a foreign substance is harmful or not.
What are antigens, immunogens, and tolerogens?
Antigens are any particle that can be recognized by the immune system. An immunogen is an antigen that can trigger an immune response, that is, one that can cause immunity. (Note that not all antigens can trigger immune responses, then.) A tolerogen is an antigen that does not give rise to an immune response, and furthermore prevents the immune system from ever mounting an immune response to that antigen if it encounters it again.
What are lymphocyte receptors composed of and how are their cells activated?
T cell receptors are composed of alpha and beta chains, B cell receptors are samples of the antibodies that the cell will secrete. To activate a cell, the receptors must bind and specific enough antigen, several nearby receptors must also be bound, and other cell surface molecules must also be involved (accessory interactions or costimulation).