Ebook How the immune system works (5th edition): Part 2
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Ebook How the immune system works (5th edition): Part 2
LECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2ich penetrate our barrier defenses. During an infection, rare T cells must find antigen presenting cells that display their cognate antigen, and B cells must encounter helper I cells which can assist them in producing antibodies. The secondary lymphoid organs make it possible for antigen presenting Ebook How the immune system works (5th edition): Part 2cells, T cells, and B cells to meet under conditions that favor activation, Ihe trafficking of immune system cells throughout our body is controlled bEbook How the immune system works (5th edition): Part 2
y the modulated expression of adhesion molecules on the surface of these cells. Virgin and experienced lymphocytes move in different traffic patterns.LECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2in producing antibodies, that Th cells must first be activated by finding an antigen presenting cell which is displaying its cognate antigen. Then the B cell must find that same antigen displayed in a fashion which crosslinks its receptors. And finally, the B cell must find the activated Th cell. Wh Ebook How the immune system works (5th edition): Part 2en you recognize that the volume of a T or B cell is only about one one-hundred-trillionth of the volume of an average human, the magnitude of this "fEbook How the immune system works (5th edition): Part 2
inding” problem becomes clear. Indeed, it begs the question, "How could a B cell ever be activated?"The answer is tiuit the movements of the various iLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2red to the locations within the body where they arc needed. Consequently, to really understand how this system works, one must have a dear picture of where in the body all these interactions take place. So it is time now for US to focus on the "geography" of the immune system.The immune system's def Ebook How the immune system works (5th edition): Part 2ense against an attacker actually has three phases: recognition of danger, production of weapons appropriate for the invader, and transport of lhese wEbook How the immune system works (5th edition): Part 2
eapons to the site of attack. The recognition phase of the adaptive immune response takes place in the secondary lymphoid organs. These include the lyLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2id organs, what are the primary ones? The primary lymphoid organs are the bone marrow, where B and T cells are born, and the thymus, where T cells receive their early training.LYMPHOID FOLLICLESAll secondary lymphoid organs have one anatomical feature in common: They all contain lymphoid follicles. Ebook How the immune system works (5th edition): Part 2These follicles are critical for the functioning of the adaptive immune system, so we need to spend a little time getting familiar with them. LymphoidEbook How the immune system works (5th edition): Part 2
follicles start life as "primary" lymphoid follicles: loose networks of follicular dendritic cells (FDCs) embedded in regions of the secondary lymphoLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2Sysirw tWrfe, Fifth Edition Lauren Sompaync. © 2016 John Wiley * Sons, Ud Published 2016by John Wiley & Sons, Ltd.LECTURE 7 Secondary Lymphoid Organs a._______________________Although FIX 1*5 do have a starfish-like shape, they are very different from the antigen presenting dendritic cells (ix:s) we Ebook How the immune system works (5th edition): Part 2 talked about before, those dendritic cells are white blood cells that are produced in the bone marrow, and which then migrate to their sentinel positEbook How the immune system works (5th edition): Part 2
ions in the tissues. Follicular dendritic cells are regular old cells (like skin cells or liver cells) tliat take up their final positions in the secoLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2nly ate the origins of follicular dendritic cells and antigen presenting dendritic cells quite different, these two types of starfishshaped cells have very different functions. Whereas the role of dendritic APCs is to present antigen to T cells via MHC molecules, the function of folliculardendriticc Ebook How the immune system works (5th edition): Part 2ells is to display antigen to B cells. I lore's how this works.Early in an infection, complement proteins bind to invaders, and some of this complemenEbook How the immune system works (5th edition): Part 2
t-opsonized antigen will be delivered by the lymph or blood to the secondary lymphoid organs. Follicular dendritic cells that reside in these organs hLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2tigen. In this way, follicular dendritic cells become "decorated" with antigens that are derived from the battle being waged out in the tissues. Moreover, by capturing large numbers of antigens and by holding them close together, FDCs display antigens in a way that can crosslink B cell receptors. La Ebook How the immune system works (5th edition): Part 2ter during live battle, when antibodies have been produced, invaders opsonized by antibodies also can be retained on the surface of follicular dendritEbook How the immune system works (5th edition): Part 2
ic cells - because FDCs have receptors that can bind to the constant region of antibody molecules.So follicular dendritic cells capture opsonized antiLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2ognate antigens hanging from these follicular dendritic "trees" proliferate to build up their numbers. And once this happens, the follicle begins to grow and become a center of 15 cell development. Such an active lymphoid follicle is called a "secondary lymphoid follicle" or a germinal center. The r Ebook How the immune system works (5th edition): Part 2ole of complement-opsonized antigen in triggerbig the development of a gennúial center cannot be overemphasized: Lymphoid follicles in humans who haveEbook How the immune system works (5th edition): Part 2
a defective complement system never progress past the primary stage. Thus, we see again that for the adaptive immune system to respond, the innate syLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2e" signals, they will commit suicide (die by apoptosis). Fortunately, helper I cells can rescue these 15 cells by providing the co-stimulation they need. Indeed, when a 15 cell whose receptors have been crosslinked by antigen receives this co-stimulatory signal, it is temporarily rescued from apoplo Ebook How the immune system works (5th edition): Part 2lic death, and continues to proliferate.t he rate al which 15 cells multiply in a germinal center is truly’ amazing: I he number of 15 cells can doublEbook How the immune system works (5th edition): Part 2
e every 6 hours! These proliferating B cells push aside other 15 cells that have not been activated, and establish a region of the germinal center calLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2ndary Lymphoid Organs and Lymphocyte TraffickingAfter this period of proliferation, some of the B cells "choose" to become plasma B cells and leave the germinal center. Others, during their time of proliferation, undergo somatic hypermutation to fine-tune their receptors. After each round of hypermu Ebook How the immune system works (5th edition): Part 2tation, the affinity of the mutated BCR is tested. Those B cells whose mutated BCRs do not have a high enough affinity for antigen will die by apoptosEbook How the immune system works (5th edition): Part 2
is, and will be eaten by macrophages in the germinal center. In contrast, B cells are rescued from apoptosis if the affinity of their receptors is greLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2t are present in the light zone of the germinal center. The current picture is that B cells "cycle" between periods of proliferation and mutation in the dark zone and periods of testing and re-stimulation in the light zone. Sometime during all this action, probably in the dark zone, B cells can swit Ebook How the immune system works (5th edition): Part 2ch the class of antibody they produce.In summary, lymphoid follicles are specialized regions of secondary lymphoid organs in which B cells percolate tEbook How the immune system works (5th edition): Part 2
hrough a lattice of follicular dendritic cells that have captured opsonized antigen on their surface. B celts that encounter their cognate antigen andLECTURE 7Secondary Lymphoid Organs and LymphocyteTraffickingHEADS UP!I he secondary lymphoid organs are strategically placed to intercept invaders whi Ebook How the immune system works (5th edition): Part 2hoid follicles are extremely important for B cell development. I hat’s why all secondary lymphoid organs have them.HIGH ENDOTHELIAL VENULESA second anatomical feature common to all secondary lymphoid organs except the spleen is the high endothelial venule (IIEV). The reason IIEVs arc so important is Ebook How the immune system works (5th edition): Part 2 that they are the "doorways" through which B and T cells enter these secondary lymphoid organs from the blood. Most endothelial cells that line the iEbook How the immune system works (5th edition): Part 2
nside of blood vessels resemble overlapping shingles which are tightly "glued" to the cells adjacent to them to prevent the loss of blood cells into tGọi ngay
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