Cytopathic Autoantibodies and Postcapillary Venules - Essay Example

A. There is no antibody production. There is the destruction of the tissues involved and the organs fail to maintain their normal function.
B. Cytopathic autoantibodies: This is the correct answer. Antibodies that are directed against one or more of the individual's own proteins are known as autoantibodies. Cytopathic autoantibodies cause degeneration of the cells they affect. In Grave's disease, the autoantibodies are directed against the TSH receptor and mimic the action of TSH, stimulating adenyl cyclase and increased release of thyroid hormones resulting in thyrotoxicosis. The antibody is known as a long-acting thyroid stimulator or thyroid-stimulating immunoglobulin. Another similar autoantibody is called thyroid growth-stimulating immunoglobulins to cause the growth of thyroid follicular epithelium. Similar T cell-mediated autoantibody response causes infiltrative ophthalmopathy (Maitra, p.1172).

C. Delayed type hypersensitivity: Inflammatory reactions initiated by mononuclear leukocytes are known as delayed hypersensitivity reactions. These reactions are mediated by T cells and monocytes/macrophages rather than by antibodies and are a major mechanism of defense against various intracellular pathogens. They also occur in transplant rejection and tumor immunity. This reaction is not seen in Graves' disease. Hence this is not the correct answer (Hinshaw, eMedicine).
D. Immediate hypersensitivity: Immediate hypersensitivity is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. The plasma cells secrete IgE. The effects of this reaction are vasodilatation and smooth-muscle contraction. Hence this is not the correct answer.
E. Immune complex disease: Combination of an epitope with an antibody is an immune complex reaction. The effects are due to the deposition of these complexes in various organs. This type of reaction is not seen in Grave's disease. Hence this is not the correct answer.

References: Hinshaw, Walter. "Hypersensitivity Reactions, Delayed." eMedicine from WebMD. http://www.emedicine.com/med/topic1100.htm
Maitra, Anirban, & Abbas, Abul. “The Endocrine System.” Robbins and Cotran Pathologic Basis of Disease. 7th ed. Philadelphia: Saunders Publishers, 2007, p.1172
Question 14
A 12-year-old boy presents with a 5-day history of sore throat. His temperature is 38.7°C (103°F). Physical examination reveals inflamed tonsils and swollen cervical lymph nodes. Entry of blood-borne lymphocytes into the cervical lymph nodes in this patient occurs primarily at which of the following locations?
A. Medium-sized arteries
B. Medium-sized veins
C. Postcapillary venules: correct answers
D. Precapillary arterioles
E. Vasa vasorum

A. Medium-sized arteries: These are also known as muscular arteries. In these arteries, the regional blood flow and blood pressure are regulated by changes in lumen size through vasoconstriction or vasodilatation. Extravasation of cells does not occur in these arteries. Hence this is not the correct answer (Schoen, p.512).
B. Medium-sized veins: Blood to the medium-sized veins arrives after it traverses the venules and small-sized veins. The vascular leakage and leukocyte exudation occur in the postcapillary venules level and blood which enters medium-sized veins are carried into the large veins. Hence this is not the correct answer.

C. Postcapillary venules: The post-capillary venules, which are known as the recirculating route of T lymphocytes in normal animals, are thought to be the pathway of migrating B lymphocytes (Kotani, 299). They are the main sites for leukocyte extravasation. Blood from capillary beds flows initially into the post-capillary venules and then sequentially through the collecting venules and veins. In inflammation, vascular leakage and leukocyte exudation occur in the postcapillary venules (Schoen, p.513). Hence this is the correct answer.

D. Precapillary arterioles: This is not the correct answer. These are the principal points of physiologic resistance to blood flow. These vessels adjust their diameters and influence blood flow distribution among various capillary beds. Blood flows from them into the capillaries.
E. Vasa vasarom: This comprises a network of small arterioles, capillaries, and venules that supply the outer tissues of large blood vessels like the aorta. The vasavasorum provides the vessel walls that they penetrate with metabolites. This facility is essential for the large vessels because their walls are thick. They do not bear any relationship with the lymph nodes. Read More