Which of these is an immune-privileged site?
Correct Answer: Seminiferous tubules
Description: Ans. d. Seminiferous tubules (Ref: Gray's 40/e p52; Robbins 9/e p214; Ganong 24/e p420)Seminiferous tubule of testis is an immune-privileged site.Some antigens are hidden (sequestered) from the immune system, because the tissues in which these antigens are located do not communicate with the blood and lymph. As a result, self-antigens in these tissues fail to elicit immune responses and are essentially ignored by the immune system. This is believed to be the case for the testis, eye, and brain, all of which are called immune- privileged sites because it is difficult to induce immune responses to antigens introduced into these sites. If the antigens of these tissues are released, for example, as a consequence of trauma or infection, the result may- be an immune response that leads to prolonged tissue inflammation and injury. This is the postulated mechanism for post-traumatic orchitis and uveitis."-- Robbins 9/e p214"The fluid in the lumen of the seminiferous tubules is quite different from plasma; it contains very little protein and glucose but is rich in androgens, estrogens, K+, inositol, and glutamic and aspartic acids. Maintenance of its composition depends on the blood-testis barrier. The barrier also protects the germ cells front blood borne noxious agents, prevents antigenic products of germ cell division and maturation from entering the circulation and generating an autoimmune response. and may help establish an osmotic gradient that facilitates movement of fluid into the tubular lumen. "--Ganong 24/e p420"Endogenous derangements of the immune system may also contribute to the loss of immunologic tolerance to self-antigens and the development of autoimmunity. Some autoantigens reside in immunologically privileged sites, such as the brain or the anterior chamber of the eye. These sites are characterized by the inability of engrafted tissue to elicit immune responses. Immunologic privilege results from a number of events, including the limited entry of proteins from those sites into lymphatics, the local production of immunosuppressive cytokines such as transforming growth factor B, and the local expression of molecules (including Fas ligand) that can induce apoptosis of activated T cells. Lymphoid cells remain in a state of immunologic ignorance (neither activated nor anergized) with regard to proteins expressed uniquely in immunologically privileged sites. --Harrison 19/e p377e-2immune- Privileged Sites* Some antigens are hidden (sequestered) from the immune system, because tissues in which these antigens are located do not communicate with blood & lymph.* As a result, self-antigens in these tissues fail to elicit immune responses and are essentially ignored by the immune system.Immune- Privileged Sites* TestisQ* Eye (Anterior camber)Q* Placenta & fetusQ* BrainQ Circumventricular Organs* These organs have fenestrated capillaries & because of their permeability they are said to be outside the blood brain barrier.* Some of them function as neurohemal organ (areas in which polypeptides secreted by neurons enter the circulation). Circumventricular Organs includes (SAMPO) * Subfornical organQ* Area postremaQ* Median eminence of hypothalamusQ* Posterior pituitary (neurohypophysis)Q* Organum vasculosum of lamina terminalisQ
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