A 23-year-old man comes to the physician with dysuria and increased urinary frequency. He is an active duty member of the US military and recently returned from sub-Saharan Africa, where he had been stationed for the last year. The patient's symptoms have persisted for several months and have failed to resolve following antibiotic treatment. His blood eosinophil count is elevated. Urine microscopy shows schistosome eggs. He is started on praziquantel and experiences improvement in his symptoms. The elevated eosinophils in this patient contribute to the host defense against schistosomiasis through which of the following mechanisms?

Question

A 23-year-old man comes to the physician with dysuria and increased urinary frequency.  He is an active duty member of the US military and recently returned from sub-Saharan Africa, where he had been stationed for the last year.  The patient's symptoms have persisted for several months and have failed to resolve following antibiotic treatment.  His blood eosinophil count is elevated.  Urine microscopy shows schistosome eggs.  He is started on praziquantel and experiences improvement in his symptoms.  The elevated eosinophils in this patient contribute to the host defense against schistosomiasis through which of the following mechanisms?

Quizplus · Accepted Answer

11ec160b_37a0_8269_9249_139ef40b2292_MD0001_00 Eosinophils perform the following functions: Parasitic defense: Eosinophil proliferation and activation during multicellular parasitic infection is stimulated by IL-5 produced by T_H2 and mast cells (not to be confused with IL-4, which stimulates IgE production). When a parasite invades the mucosa or enters the bloodstream, it is coated by IgG and IgA antibodies that bind the Fc receptors located on the eosinophil cell surface. This triggers eosinophil degranulation and release of cytotoxic proteins (eg, major basic protein) and reactive oxygen intermediates, substances that damage and destroy antibody-bound parasites. This mechanism is an example of antibody-dependent cell-mediated cytotoxicity (ADCC), which is also used by macrophages, neutrophils, and natural killer cells. Type I hypersensitivity reactions: Eosinophils also synthesize prostaglandins, leukotrienes, and cytokines that contribute to the inflammation seen in late-phase type 1 hypersensitivity and chronic allergic reactions. (Choice B) Eosinophils contain a diverse number of immunomodulatory cytokines that are important for directing the T_H2 immune response; but they do not significantly affect B cell chemotaxis. (Choice C) Complement activation is an important step in antibody-mediated (type II) and immune complex mediated (type III) hypersensitivity reactions. Complement does not play a prominent role in the destruction of parasites by eosinophils. (Choice D) Immediate (type I) hypersensitivity reactions are primarily mediated by mast cells and basophils. These cells possess Fc receptor-bound IgE on their membranes. Eosinophils contribute to late-phase type 1 hypersensitivity, but this is an allergic response that would not be protective against schistosomiasis. (Choice E) Eosinophils can phagocytose parasitic antigens and present them in association with MHC class II molecules to stimulate helper T lymphocytes. In contrast, MHC class I antigen processing is involved in inducing a cytotoxic T lymphocyte response against intracellular pathogens (eg, viruses). Educational objective: Eosinophils play a role in host defense during multicellular parasitic infection. When stimulated by antibodies bound to a parasitic organism, they destroy the parasite via antibody-dependent cell-mediated cytotoxicity with enzymes from their cytoplasmic granules. Another function of eosinophils is regulation of type I hypersensitivity reactions. __________ References: IgE, mast cells, basophils, and eosinophils. (http://www.ncbi.nlm.nih.gov/pubmed/20176269)

A 23-Year-Old Man Comes to the Physician with Dysuria and Increased