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Section IX: Rheumatology and Immunology

All of the following are key features of the innate immune system EXCEPT:

A. Exclusively a feature of vertebrate animals

B. Important cells include macrophages and natural killer lymphocytes

C. Nonrecognition of benign foreign molecules or microbes

D. Recognition by germline-encoded host molecules

E. Recognition of key microbe virulence factors but no recognition of self-molecules

The answer is A. (Chap. 372e) The innate immune system is phylogenetically the oldest form of immunologic defense system, inherited from invertebrates. This defense system uses germline-encoded proteins to recognize pathogen-associated molecular patterns. Cells of the innate immune system include macrophages, dendritic cells, and natural killer lymphocytes. The critical components of the innate immune system include recognition by germline-encoded host molecules and recognition of key microbe virulence factors, but no recognition of self-molecules and of benign foreign molecules or microbes. Adaptive immunity is found only in vertebrate animals and is based on generation of antigen receptors on T and B lymphocytes by gene rearrangements, such that individual T or B cells express unique antigen receptors on their surface capable of recognizing diverse environmental antigens.

A 29-year-old man with episodic abdominal pain and stress-induced edema of the lips, tongue, and occasionally larynx is likely to have low functional or absolute levels of which of the following proteins?

A. C1 esterase inhibitor

B. C5A (complement cascade)

C. Cyclooxygenase

D. Immunoglobulin (Ig) E

E. T-cell receptor, α chain

The answer is A. (Chap. 372e) Complement activity, which results from the sequential interaction of a large number of plasma and cell membrane proteins, plays an important role in the inflammatory response. The classic pathway of complement activation is initiated by an antibody-antigen interaction. The first complement component (C1, a complex composed of three proteins) binds to immune complexes with activation mediated by C1q. Active C1 then initiates the cleavage and concomitant activation of components C4 and C2. The activated C1 is destroyed by a plasma protease inhibitor termed C1 esterase inhibitor. This molecule also regulates clotting factor XI and kallikrein. Patients with a deficiency of C1 esterase inhibitor may develop angioedema, sometimes leading to death by asphyxia. Attacks may be precipitated by stress or trauma. In addition to low antigenic or functional levels of C1 esterase inhibitor, patients with this autosomal dominant condition may have normal levels of C1 and C3 but low levels of C4 and C2. Danazol therapy produces a striking increase in ...

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