Anatomy and physiology of the immune system Flashcards
Where do dendritic cells tend to interface at?
What helper T cells migrate from the deep cortex (paracortex) into the follices to activate B cells?
Dendritic cells that arrive in the afferent lymph tend to gather at the interface between the cortex (mostly B cells, arising from the bone marrow) and the paracortex (mostly T cells, arising from the thymus).
Follicular helper T cells (Tfh) migrate from the deep cortex into the follicles where they help B cells get activated.
What is the pattern of recirculation of lymphocytes?
How are endothelial cells of postcapillary venules unusual?
Where do lymph vessels drain into?
What are the two lymphocyte circulations?
Where do lymphocytes cross from blood to lymph?
Where do lymphocytes cross from lymph to blood?
A lymphocyte in the blood encounters the cells lining certain ► postcapillary venules in the peripheral lymphoid tissues, especially lymph nodes.
-These endothelial cells are unusual. How? They are not flat as is the usual case, but high and cuboidal. Recirculating lymphocytes may bind to and pass between the endothelial cells into the lymph node, where they may stay, or move eventually into the lymph which drains from that lymph node to the next in the chain.
Lymph works its way into the largest lymph channels, importantly the thoracic duct; from there it is emptied into the venous blood and the circulatory loop starts over again.
Thus there are two lymphocyte circulations, blood and lymphatic, in which lymphocytes cross from blood to lymph at the nodes, and from lymph back to blood at the heart.
Note that in all tissues, leukocytes preferentially leave the blood via postcapillary venules; but the ones in the lymph nodes are specialized for high-turnover recirculation.
Explain spleen anatomy:
What pulp of the spleen corresponds to the medulla in lymph nodes?
Which pulp is capable of making red cells when neccesary?
The spleen is the most important store of what?
What type of cells are those sorrounding the white pulp?
Spleen has red and white pulp.
The red pulp roughly corresponds to the medulla in lymph node, containing lots of phagocytic cells and capable of making red cells when necessary.
- Red pulp makes the spleen the body’s most important filter of particulates, such as bacteria or damaged platelets.
- The spleen is also the most important store of monocytes.
- The white pulp consists of islands of cells. The sheath of cells which surrounds the central arteriole is mostly T cells; the more diffuse collection of cells further from the arteriole is mostly B cells, so the spleen is like a huge lymph node, too.
Gut-Associated Lymphoid Tissue
What structures underlie the mucosa in the small intestine?
What are M cells?
Where do Peyer patches drain into?
The gut, with its large and, of necessity, permeable surface, has the largest collection of secondary lymphoid tissue in the body, sometimes called GALT or MALT (gut- or mucosa-associated lymphoid tissue.)
Lymph node- like structures called Peyer patches underlie the mucosa, especially in the small intestine. The functional structure of the Peyer patches includes ► specialized mucosal M cells, which are gatekeepers, ingesting proteins and particles as big as a virus and transporting them to the abluminal side. There a rich content of dendritic cells acquire antigens and carry them to the adjacent B cell follicles and T cells zones of the Peyer’s patch.
The patches themselves drain to a large collection of mesenteric lymph nodes. It is here where the body has to solve its most difficult problem: Is this foreign stuff (food, normal gut bacteria) harmless, or is it dangerous?
What is an immunogen?
What is a tolerogen? What is special about it?
Antigen refers to a substance which can be recognized by the immune system.
►An antigen frequently is also an immunogen , which is an antigen in a form which can give rise to an immune response, that is, which can immunize. For example, an isolated antigenic determinant (see below) is not usually an immunogen; it can be recognized by antibody, but is too small to trigger an immune response. Competing Ebola (EBOV) vaccines, all nicely antigenic, are being tested to see which is the best immunogen .
A tolerogen is antigen delivered in a form, or by a route, which does not give rise to an immune response, and which furthermore prevents an immune response to subsequently administered immunogen which has the same antigenic determinants — to be discussed later. You can imagine how useful a tolerogen might be. We don’t have any clinical tolerogens at present …or do we? We’ll discuss this under Type 1 immunopathology.
Lymphocyte differentiation
When a stimulated T cell becomes large and differentiated, it is called a (T) lymphoblast.
A B cell also becomes a (B) lymphoblast and then goes beyond that to the incredibly specialized plasma cell , with an enormous protein-making rough endoplasmic reticulum (RER). They work so hard to pump out antibody that many of them will die in a few days; others back off a few notches and remain as long-term memory cells.
