----start immuno.lec 1/3/97--------- course 6001 immunology Dr Weber 407 rosenthal x8859 If there are problems with the course go see him, the door is usually open, no need to make an appt. It is recommended to sit down with a beer and go over the beginning of the handout. Buy the book - the purple one. There is a CD ROM for one of the other books that we can use. Scientific American special issue: Life, Death, and the Immune System - try to get hands on a copy. It's probably useful to read the chapters in the book before coming to lecture. [I guess I better go buy this book today...] Immunology is very conceptual. Use lots of pencil and paper and make drawings of T and B cells and Macrophages, draw receptors and arrows. What IS immunology? the subject dealing with all the defense mechanisms the vertebrates have evolved to deal with the onslaught of infectious organisms. It can be divided into INNATE and ACQUIRED immune systems. Pathogens can be either intracellular or extracellular. They can be phagocytosed bacteria resisting degradation, or free floating parasites in the blood. You can have a virus infected cell in a mucosal surface, or you can have bacteria sitting on top of the mucosal epithelium. How does the immune system kill intracellular pathogens? needs to get rid of the infected cell..... There can be intracellular parasites in muscle tissue...or there can be organisms in body cavities eg worms in the gut. How does the body kill a cell holding phagocytosed bacteria? Eg, TB? Cell mediated immunity: cytokines. Say an abcess forms, and there is a bunch of bacteria within the tissue. Many bacteria release exotoxins, eg tetanus, and some have endotoxin in their cell walls. How does the immune system get rid of these bacteria? Antibody will work, bacteria will be phagocytosed, hopefully. Keep these ideas in mind - it's important. There are other pathogens...rickettsia, fungi, etc, but this is an overview. INNATE and ACQUIRED IMMUNITY Innate: something you are born with, functions immediately upon exposure to pathogen, but has no specificity. Can be quite capable of clearing infectious organism without involving acquired immunity. but mostly, not capable, and then you get sick, and then acquired immunity kicks in. Acquired: must first have exposure to an antigen. There is exquisite specificity. There is immunological memory. SELF VS NONSELF in primary contact to an antigen, if you look at innate immunity, it works the same way each time, while with acquired immunity, the second contact provokes a more extensive reaction and specific memory. in order to accomplish immunological functions, cells have to recognize self from nonself. You don't want to make antibody against your own insulin, your own thyroglobulin, etc etc. INNATE IMMUNE SYSTEM soluble plasma components: interferon, lysozyme, complement, acute phase proteins eg CRP cells: phagocytes (macrophages, neutrophils, eosinophils), NK cells **question: i was taught before that skin is part of innate immunity...yes or no?** ACQUIRED IMMUNE SYSTEM: T, B cells and macrophages, etc How do most organisms enter the body? skin is a formidable barrier being dry and not allowing bacterial growth very much. sebacious gland secretions are anti bacterial, mucosal linings of GI and respiratory tract also have good innate defenses, being lined with mucus which holds proteolytic enzymes and also IgA. In the GI tract there is also the normal flora which inhibits the growth of pathogens. But if you take abx and destroy normal flora you may have a pathogen emerge. also cilia of respiratory epithelium are helpful. lysozyme will cleave proteoglycans on the surface of bacteria and allows water to enter the cell and kill the bacteria. COMPLEMENT a bunch of plasma proteins which interact sequentially on the surface of bacteria, viruses, or one's own cells. there are about 9 components which interact sequentially, with an end result being: -lysis of bacteria: complement punches hole in bacteria -causes chemotaxis: activates phagocytes to come eat bacteria -opsonizes bacteria: targets the bacteria for phagocytosis. OPSONIZATION: C3b is a better opsonin than antibody alone, but antibody and C3b is even better. Of course, without an opsonin, there will be some phagocytosis, but with an opsonin, it works better, because the phagocytes have special receptors for the opsonins. Eg, the phagocyte has a C3b receptor, and has an Fc receptor to bind the constant region of the Ab - so when Ab and C3b are present, the binding of phagocyte and target cell is vastly improved. ANTIBODY is a flexible adaptor. * * - binding sites-where it binds Ag \ \ / / \ \/ / -Fab variable region | | | | -Fc constant region | | ACUTE PHASE PROTEINS: made during acute infection. when you have an acute infection you start seeing these plasma proteins, peaking in 4-6 days, and they go away when infection ends. they have no specificity and are part of innate immunity. C reactive protein: an acute phase protein which Interacts with something on bacteria, coats it, and activates complement the APPs are made in the liver. Macrophages which phagocytose and become active in the presence of pathogens secrete IL-6. IL-6 acts on hepatocytes to induce sysnthesis of acute phase proteins including mannose binding protein. So does IL-1. The action of these cytokines is temporary, so when the infection goes away the hepatocytes stop doing this. also realize this kicks in BEFORE acquired immunity does. this is immediate. mannose binding protein activates complement to lyse bacteria and also directly opsonizes the bacteria fibrinogen is another APP. if an abcess forms, it becomes walled off and fibrinogen becomes fibrin and helps to keep the bacteria separate. in large animals the measure of fibrinogen in the blood is a better measure of acute inflammatory response than a WBC. INTERFERONS another important innate defense. two kinds: non-immune eg IFNa and IFNb, and immune, eg IFNg. Now, the infected cells make IFNa and b, these are produced when a virus infects a cell. But IFNg is produced by activated Thelper cells after interaction with an antigen. what good is interferon? IFNa and IFNb are part of the innate immune system. what do they do? other cells have IFN receptors. IFN inhibits viral replication in a cell, inhibits transcription of RNA - interferes with things! The cell originally infected with the virus will die, and the neighboring cell will pick up the IFN on the receptor and inhibit the viral replication - but it may still die, but it will make more interferon. (when the IFN receptor binds IFN, the cell starts making IFN, even before being infected.) So, the virus isn't able to replicate well in the presence of interferon even though the cells still die, you will run out of virus... IFN appears rapidly in the presence of an infection and peaks just before you start making reasonable amounts IgM or IgG. if you give IFN Abs to mice, you can drastically increase susceptibility to viral infection. NK cells: natural killers :) a heterogeneous group of cells - many of which are large granular lymphocytes. many have azurophilic granules that are very distinct. they are produced in the bone marrow but do not travel through the thymus. they can kill some tumor cells by recognizing abnormal surfaces, and can also kill viral infected cells. no known specific recognition by the NK cells of tumors or viruses. Just kind of generic. Must be intimate contact between NK cell and target cell. NK cells have many receptors, including the Fc receptor. Also a putative NK receptor may be present, most people say it isn't. but NK cells CAN see MHC (group of genes responsible for glycoproteins etc which cover cells, MHC I or II). the MHC antigens on cell surfaces are very important for Ag presentation. the NK cells apparently can detect when a normal cell has less than its normal array of MHC on the surface. viral infected and tumor cells have less MHC so the NK cell will kill them. it does this by making holes in the target cell membrane by secreting proteins called perforins which line up in the membrane andmake holes (like complement). NK cells do not express an Ag specific receptor do express Fc receptor called LGLs active against tumors, virus infected cells, bacteria, parasites, and Ab coated cell targets. antibody dependent cellular cytotoxicity: if you have a cell with antigen on the surface there may be an Ab response by the body, but if the Ag is weak, response will be weak. So the Ab binds to the Ag with the variable binding site, and the Fc portion is sticking up off the cell surface. The NK cells can then kill the target cell, because its Fc receptor will bind to the Fc region, crosslinking Ab molecules and causing perforation of cell membrane. understand that the binding of the Fc receptor to the Fc region of Ab is totally nonspecific. any cell with an Fc receptor can do the same thing, btw. [end of discussion of innate defenses] ---break--- [he says he's going to get faster now...argh] PHAGOCYTOSIS: stuff is phagocytosed into phagosome, which joins with lysosome, becomes phagolysosome, then digestive vacuole, then residual body, etc. these phagocytic cells eg magrophages are ANTIGEN PRESENTING CELLS> they come from bone marrow as monocytes, then diverge into kupffer cells of the liver, alveolar mphages of lung, histiocytes of CT, BM, microglial cells of brain. when we discuss antigen presentation we think of Langerhan's cells, interdigitating cells, and follicular dendritic cells: which are ALL dendritic cells, found in skin, thymus, or LN, or a B cell, or sometimes a macrophage after it is activated. but B cells and dendritic cells always express MHC class II so are "professional" APCs. macrophages only express MHC II after being activated. these cells also have Fc receptors. the macrophage is the best phagocyte of these cells. the others take things in via pinocytosis, less efficiently. langerhans cells in the skin: dendritic cells of skin. assume it picks up some antigen somehow. the cell then travels via lymphatics to the LNs, where they are called "interdigitating cells" or "veil cells" during their travel. They present antigen to T cells there.They do this in a germinal follicle Tcell zone. cytokines are liberated and nearby B cells proliferate and produce the antibody factories called PLASMA CELLS. but that only happens after the interdigitating cells present antigen to T cells causing cytokine release. this is what happens when you give a vaccination.. there are follicular dendritic cells but we don't know the origin of those except they do come from bone marrow. but they are also APCs. quick review of cell lines. bone marrow makes all the cellular elements of the blood, from a STEM cell. the stem cell becomes MYELOID STEM CELL which is precursor of all granulocytes and the megakaryocyte and the erythrocyte and the mast cell. the STEM CELL also becomes a LYMPHOID STEM CELL which becomes B cell precursors, T cell precursors, and possibly NK cells. NK may come right from stem cell. note that in BM, B cells develop IgM and IgD and then are ready to respond to Ag, so can then circulate and proliferate into plasma cells/memory cells. CD5 B cells. we dont know what they are. they end up in peritoneal cavity and have very limited repertoire re: Ag specificity. they respond mostly to polysaccharides which are a major part of bacteria. they carry mostly IgM on their surfaces. they are a self renewing population but in contrast to other B cells they don't switch to making IgG, they only make the IgM so there is no memory in these cells. every time there is an infection int he peritoneal cavity they do the same thing. what are these cells doing there? possibly an evolutionary relic of an interface between innate and acquired immunity. surely they are there to help ward off infection. no immunological memory, no switching mechanism. strange. T cells become T helpers Th cells and cytotoxic T cells Tc cells. the Th2 cells make cytokines to help B cells. the Th1 cells make cytokines that activate macrophages. eg if youhave TB inside an Mphage, once Th1 are active and they recognize TB they make IFNg to activate the Mphage and then the Mphage can kill the TB. the Tc cells are primarily responsible for killing virally infected cells. if you want to get rid of the viral infection you have to get rid of the infected cells and these Tc cells do that using a mechanism similar to that used by NK cells except involving specific recognition. analogous to CD5B cells are the gammadelta T cells or gd T cells, which form in thymus or extrathymic area. they have a limited repertoire of specificity, and can't respond to many antigens. they have a restricted type of response. they end up in the skin and mucosae of the body. they respond to so called heat shock proteins. heat shock proteins are produced by cells under stress like heat or cold. these proteins work in assembling and folding and transporting other proteins in the cell, but they also get to the surface.they are made by bacteria and normal cells. these gdTcells respond to these heat shock proteins. a primitive defense mechanism against bacterial invasion on these mucosal surfaces. WHERE DOES IT START? Fetal lymphoid tissues and organs starts as very small islands near the paraaortic arch. then you get a thymus, the bone marrow, the liver and the spleen. in adults mostly the bone marrow takes over producing B cells and sending Tcell precursors to the thymus. now, we weretold that the thymus involutes...but it DOES persist in a rudimentary form. if there is a need at some form in a later life for more T cells, the thymus can become very functional - eg if pt gets chemo or radiation and needs to repopulate w/T cells can do it.the medulla of the thymus always remains as a rudiment. in chicken the B cells are made int he bursa of fabricius attached to the cloaca. there are a string of thymus glands, a tiny spleen, and the B of F as lymphoid organs in the chicken. so, where do B cells come from in the adult avian immune system? not bone marrow, but already Ig positive cells through "gene conversion" which allows new B cells with different specificity to be produced. but there is no more production from the germ line as in mammals. for most species of fish (except jawless fish) they already have a thymus and spleen. but bone marrow isn't present except in frogs/toads, reptiles, birds and mammals. if you look at jawless fish, which have no thymus, they seem to make IgM for which youdo not need different T cell classes. Lungfish, which have bone marrow do make IgG. birds make IgA as well...but you must have a THYMUS to make multiple types of Ig. Lymphocyte recirculation: skipping "what is primary and secondary lymphoid organ" except primary == thymus, bone marrow: production of cells in these structures is antigen independent. secondary == LN, spleen, peyers patches. production of cells is antigen driven there. assume all the cells are made etc. how do they know they are going to recirculate, how do they end up in the right place. it's pretty random for most of the body. cells move around randomly through CT etc. now, with spleen, bone marrow, lung, and liver, the endothelium through whichlymphocytes migrate may have certain adhesion factors so may arrest the lymphocytes in those regions. so, pig with respiratory infxn will make cytokines that cause adhesion factors to appear on endothelium to stop immune cells in the lung region. what structure in a LN do cells come out of to get to the T cell area? post capillary venules in the LN which have "high endothelium" which has a lot of receptors which allows lymphocytes to adhere. so the migration of lymphocytes in the body: left ventricle, aorta, postcap venule of LN, emigrate from high endothelial region, leave through efferent lymphatics, drain into veins, return to heart. take a look at the diagram in the handout for more info!! so T cells get to T cell area, B cells go to germinal follicles, etc etc. you can show that there is a lot of adhesion of lymphocytes through high endothelium: slide. they attach and roll, get sticky and stop, and then migrate out between endothelial cells into the paracortex. Or, for B cells, migrate to germanal centers. what directs the flow of these lymphs? selectins: high affinity for carbohydrates. LNs have L-selectin onthe surface which combines w/sugar containing molecules causing stickiness of lymphocyte. integrins intercellular adhesion molecules - these form firm bond and something i missed oops. key point: lymphocytes that go into LN, are mostly naive T cells, anyway, they migrate in, and the recognition mechanism is based primarily on L selectin, CD 34 and GlyCAM1. the recognition to get to peyer's patches is similar but based on different molecules. once lymphocytes are formed in peyer's patch, they tend to home back to mucosal lymphoid tisues. memory cells do not home back to LNs but tend to stay in tissues. ----end-------