USMLE Step 1 Quiz: Antigen Presentation And Cytokines

A 1-year-old boy presents with recurrent bacterial and fungal infections, including Pneumocystis jirovecii pneumonia and chronic diarrhea. Laboratory studies show severe lymphopenia, particularly of CD4+ T cells, and hypogammaglobulinemia. Flow cytometry reveals that his peripheral blood mononuclear cells fail to express HLA-DR, -DP, and -DQ molecules on their surface. This patient's defect most directly impairs which of the following immunologic processes?

This patient's defect most directly impairs which of the following immunologic processes?

A 35-year-old woman is diagnosed with tuberculoid leprosy. A skin biopsy from a lesion shows numerous granulomas containing activated macrophages and CD4+ T lymphocytes. The containment of Mycobacterium leprae within these granulomas is heavily dependent on the cell-mediated immune response. Which of the following cytokines, produced by activated T helper cells, is most critical for activating the macrophages in this patient's lesions?

Which of the following cytokines, produced by activated T helper cells, is most critical for activating the macrophages in this patient's lesions?

A 19-year-old male college student presents to the emergency department with a high fever, severe headache, nuchal rigidity, and a petechial rash. A lumbar puncture confirms a diagnosis of meningococcal meningitis caused by Neisseria meningitidis. His medical history is significant for a similar episode one year prior. A deficiency in which of the following would most likely explain his recurrent infections with this specific pathogen?

A deficiency in which of the following would most likely explain his recurrent infections with this specific pathogen?

A 30-year-old woman presents with fatigue and dark-colored urine in the morning. Laboratory studies show normocytic anemia, elevated LDH, and low haptoglobin, consistent with intravascular hemolysis. Flow cytometry of her red blood cells reveals an absence of CD55 and CD59. The lack of these proteins on the cell surface leads to uncontrolled activation of which of the following?

The lack of these proteins on the cell surface leads to uncontrolled activation of which of the following?

A 7-year-old boy with a history of severe allergies and asthma presents with an acute exacerbation after exposure to cat dander. His blood work shows marked eosinophilia. The differentiation of naive T helper cells into the Th2 subtype and the subsequent production of IgE and activation of eosinophils are primarily driven by which cytokine?

The differentiation of naive T helper cells into the Th2 subtype and the subsequent production of IgE and activation of eosinophils are primarily driven by which cytokine?

A 45-year-old man receives a kidney transplant from an unrelated donor. Despite immunosuppressive therapy, he develops acute cellular rejection 10 days post-transplantation. A biopsy of the allograft shows a dense mononuclear infiltrate. The donor's kidney cells are being targeted by the recipient's CD8+ cytotoxic T lymphocytes. Which of the following molecules must be expressed on the surface of the donor's renal tubular epithelial cells for this recognition to occur?

Which of the following molecules must be expressed on the surface of the donor's renal tubular epithelial cells for this recognition to occur?

A scientist is developing a vaccine against a virus that exclusively infects epithelial cells, which are not professional antigen-presenting cells (APCs). For the vaccine to generate a robust CD8+ T cell response, viral antigens must be presented by MHC class I molecules on dendritic cells (DCs). Since the DCs are not directly infected, they must take up exogenous viral particles or debris from infected cells. This process, where exogenous antigens are presented on MHC class I, is known as what?

This process, where exogenous antigens are presented on MHC class I, is known as what?

A 28-year-old man returns from a trip to sub-Saharan Africa and is diagnosed with a Schistosoma infection. A complete blood count is ordered. A marked increase in which of the following cell types would be expected, driven primarily by the cytokine IL-5 produced by Th2 cells?

A marked increase in which of the following cell types would be expected, driven primarily by the cytokine IL-5 produced by Th2 cells?

A clinical trial is investigating a new biologic agent for the treatment of Crohn's disease, an inflammatory bowel disease characterized by an overactive Th1 response. The agent is a recombinant form of a cytokine known to suppress the activation and proliferation of T cells and macrophages, thereby reducing intestinal inflammation. Which of the following cytokines has these potent immunosuppressive and anti-inflammatory properties?

Which of the following cytokines has these potent immunosuppressive and anti-inflammatory properties?

A 40-year-old woman is diagnosed with systemic lupus erythematosus (SLE). Her disease is characterized by the formation of immune complexes containing anti-dsDNA antibodies and nuclear antigens. These complexes deposit in various tissues, like the kidneys, leading to glomerulonephritis. The clearance of these immune complexes is a critical function of the complement system, which is initiated when which of the following molecules binds directly to the Fc portion of the antibodies in the complex?

The clearance of these immune complexes is a critical function of the complement system, which is initiated when which of the following molecules binds directly to the Fc portion of the antibodies in the complex?

A laboratory is investigating the effects of a novel viral protein that allows infected cells to evade destruction by cytotoxic T lymphocytes (CTLs). They find that cells expressing this viral protein have markedly reduced surface expression of MHC class I molecules, while MHC class II expression is unaffected. Further analysis shows that peptides derived from cytosolic proteins are being generated normally by the proteasome. The viral protein most likely interferes with which of the following cellular components?

The viral protein most likely interferes with which of the following cellular components?

A 25-year-old woman presents to the emergency department with acute swelling of her lips, tongue, and face that developed over the past few hours. She denies any new food or drug exposures. She reports similar, self-resolving episodes in the past, and her father had similar problems. Physical examination reveals non-pitting, non-pruritic edema. A deficiency in C1 esterase inhibitor is suspected. This deficiency leads to unregulated production of bradykinin due to the uncontrolled activity of which enzyme?

This deficiency leads to unregulated production of bradykinin due to the uncontrolled activity of which enzyme?

A 55-year-old woman with metastatic renal cell carcinoma is treated with a recombinant cytokine therapy designed to enhance the activity of cytotoxic T lymphocytes and natural killer (NK) cells. This therapy works by promoting the proliferation and differentiation of these effector cells. Which of the following cytokines is most likely being administered?

Which of the following cytokines is most likely being administered?

A virology researcher is studying how cytotoxic T lymphocytes (CTLs) recognize and eliminate virally infected cells. He infects a culture of human hepatocytes with a virus. He observes that CTLs from a previously infected patient efficiently lyse these infected hepatocytes. The viral proteins are first degraded in the cytoplasm of the hepatocytes. Which of the following molecules is essential for transporting the resulting peptide fragments into the endoplasmic reticulum for loading onto MHC class I molecules?

Which of the following molecules is essential for transporting the resulting peptide fragments into the endoplasmic reticulum for loading onto MHC class I molecules?

A researcher is studying antigen processing in dendritic cells. She incubates the cells with a soluble, exogenous protein antigen. She uses immunofluorescence to track the pathway of the antigen and the MHC molecules that will present it. After endocytosis, the antigen is degraded in an acidic endolysosomal compartment. Which of the following proteins prevents endogenous peptides in the endoplasmic reticulum from binding to the peptide-binding groove of newly synthesized MHC class II molecules?

Which of the following proteins prevents endogenous peptides in the endoplasmic reticulum from binding to the peptide-binding groove of newly synthesized MHC class II molecules?

A 4-year-old child presents with disseminated mycobacterial infection after receiving the BCG vaccine. Genetic analysis reveals a mutation in the gene encoding the receptor for interferon-gamma (IFN-γ). In a healthy individual, macrophages that have phagocytosed mycobacteria produce IL-12. IL-12 then acts on T cells and NK cells to stimulate their production of IFN-γ. What is the primary function of the IFN-γ that is subsequently produced in this response?

What is the primary function of the IFN-γ that is subsequently produced in this response?

A 20-year-old woman presents with pharyngitis, fever, and posterior cervical lymphadenopathy. A peripheral blood smear shows atypical lymphocytes. The infection is caused by Epstein-Barr virus (EBV), which infects B lymphocytes. For an effective immune response, viral antigens must be presented to naive CD4+ T helper cells. Which of the following cell types is considered a professional antigen-presenting cell (APC) capable of performing this function?

Which of the following cell types is considered a professional antigen-presenting cell (APC) capable of performing this function?

A 68-year-old man with a history of diabetes mellitus is admitted to the ICU with septic shock secondary to a gram-negative bacillary pneumonia. He is hypotensive (BP 80/40 mm Hg), tachycardic (HR 130/min), and febrile (Temp 39.5°C). The systemic inflammatory response in this patient, characterized by widespread vasodilation and increased vascular permeability, is primarily driven by the massive release of which of the following cytokines from activated macrophages?

The systemic inflammatory response in this patient, characterized by widespread vasodilation and increased vascular permeability, is primarily driven by the massive release of which of the following cytokines from activated macrophages?

The human major histocompatibility complex (MHC) is located on chromosome 6 and is also known as the human leukocyte antigen (HLA) system. The genes in this region are highly polymorphic, meaning there are many different alleles in the population. This polymorphism is evolutionarily advantageous because it increases the variety of peptides that can be presented to T cells. Where is the polymorphism of MHC molecules predominantly concentrated?

Where is the polymorphism of MHC molecules predominantly concentrated?

A 2-year-old boy is brought to the pediatrician with his third episode of severe pneumonia in the past year, caused by Streptococcus pneumoniae. He has also had multiple ear infections and a skin abscess. Laboratory evaluation reveals a profound deficiency in a key complement component that serves as an opsonin and is central to all three complement pathways. A deficiency in which of the following proteins is the most likely cause of this patient's susceptibility to pyogenic bacterial infections?

A deficiency in which of the following proteins is the most likely cause of this patient's susceptibility to pyogenic bacterial infections?