Antibody binds to the antigen on the cell surface

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antibody binds to the antigen on the cell surface, whereas in type III the antibody binds to soluble antigen that was released into the blood or body fluids, and the complex is then deposited in the tissues. Immune complexes can be of various sizes, depending on the relative amounts of antigen and antibody. Fairly large immune complexes are cleared rapidly from the circulation by tissue macrophages, whereas very small complexes eventually are filtered from blood through the kidneys, without any pathologic consequences. Intermediate-sized immune complexes are likely to be deposited in certain target tissues, where they have severe pathologic consequences, such as inflammation in the kidneys (glomerulonephritis), the vessels (vasculitis), or the joints (arthritis or degenerative joint disease). Example: Raynaud phenomenon, a condition caused by the temperature-dependent deposition of immune complexes in the capillary beds of the peripheral circulation (blocking circulation). Certain immune complexes precipitate at temperatures below normal body temperature, particularly in the tips of the fingers, toes, and nose, and are called cryoglobulins. The precipitates block the circulation and cause localized pallor and numbness, followed by cyanosis (a bluish tinge resulting from oxygen deprivation) and eventually gangrene if the circulation is not restored. 1. Type IV hypersensitivity reactions. Whereas types I, II, and III hypersensitivity reactions are mediated by antibody, type IV reactions are mediated by T lymphocytes and do not involve antibodies. Clinical examples of type IV hypersensitivity reactions include graft rejection and allergic reactions resulting from contact with such substances as poison ivy and metals. Intradermal injection screening for TB is a delayed response Type IV. Also indicated in in many autoimmune diseases. Autoimmune and Alloimmune Diseases Many examples of autoimmune or alloimmune diseases have been described. Several basic principles are exemplified by two examples: systemic lupus erythematosus (an autoimmune disease) and tissue rejection (i.e., transplant rejection or transfusion reaction) (an alloimmune phenomenon). Systemic Lupus Erythematosus Systemic lupus erythematosus (SLE) is a chronic, multisystem, inflammatory disease and is one of the most common, complex, and serious of the autoimmune disorders. SLE is characterized 14
NURS 611: Advanced Patho Exam 2 Study Guide by the production of a large variety of autoantibodies against nucleic acids, erythrocytes, coagulation proteins, phospholipids, lymphocytes, platelets, and many other self- components. The most characteristic autoantibodies produced in SLE are against nucleic acids (e.g., single-stranded deoxyribonucleic acid [DNA], double-stranded DNA). Deposition of circulating immune complexes containing antibody against DNA produces tissue damage in individuals with SLE. Deposition of immune complexes composed of DNA and antibody also causes inflammatory lesions in the renal tubular basement membranes, brain (choroid plexus), heart, spleen, lung, gastrointestinal tract, skin, and peritoneum.

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