Microbiology and Immunology — Core Concepts Practice Questions

A 45-year-old man presents to the emergency department after experiencing a severe allergic reaction following a bee sting. He developed generalized urticaria, angioedema, wheezing, and hypotension within minutes. He is immediately treated with epinephrine. The rapid onset of his symptoms is primarily due to the release of preformed mediators from mast cells. Which of the following is the primary mediator responsible for the rapid vascular and bronchial changes observed in this patient?

A 3-year-old child presents with a history of recurrent infections with encapsulated bacteria, along with persistent mucocutaneous candidiasis. Lab results show normal B cell and T cell counts, but a defect is identified in the ability of phagocytes to effectively kill ingested microbes, despite normal phagocytosis. Further investigation reveals a deficiency in a key complement protein responsible for opsonization. Which complement component is primarily responsible for directly opsonizing pathogens and enhancing phagocytosis?

A research study investigates the interaction between macrophages and bacterial lipopolysaccharide (LPS). When macrophages encounter LPS, they rapidly activate signaling pathways that lead to the production of pro-inflammatory cytokines and chemokines, initiating an innate immune response. Which class of pattern recognition receptors primarily mediates the recognition of bacterial LPS on macrophages?