Inmunología Flashcards
A 26-year-old woman comes to the physician because of several days of fever, abdominal cramps, and diarrhea. She drank water from a stream 1 week ago while she was hiking in the woods. Abdominal examination shows increased bowel sounds. Stool analysis for ova and parasites shows flagellated multinucleated trophozoites (Giardia). Further evaluation shows the presence of antibodies (IgA) directed against the pathogen. Secretion of these antibodies most likely requires binding of which of the following?
The binding of the CD40 membrane receptor on B cells with CD40 ligand (CD40L) on the surface of T helper cells is the second step in immunoglobulin class switching and is necessary for the secretion of IgA in patients with Giardia lamblia infection. The first step in B cell activation is the binding of antigen-presenting MHC II on B cells to the CD4 receptor on T helper cells.
What is the triad of hemolytic uremic syndrome (HUS) and which toxin is the most common cause in pediatric HUS?
This child presents with the triad of thrombocytopenia, signs of hemolysis (anemia, ↑ LDH, schistocytes), and renal dysfunction
The Shiga-toxin-producing E. coli (STEC) is the most common cause of pediatric HUS.
A 44-year-old man with HIV comes to the physician for a routine follow-up examination. He has been nonadherent with his antiretroviral medication regimen for several years. He appears chronically ill and fatigued. CD4+ T-lymphocyte count is 405/mm3. Further evaluation of this patient is most likely to show which of the following findings?
Violaceous skin lesions in a patient with HIV describe Kaposi sarcoma. HIV patients are at a higher risk of Kaposi sarcoma at variable CD4 counts, even above 400/mm3.
An investigator is conducting an experiment to develop a new drug against HIV infection. HIV-infected and uninfected CD4 T-cell lines are mixed in-vitro with a chemically modified synthetic peptide triazole complex. The complex is found to have a high binding affinity to the gp120 protein, irreversibly inhibiting its function and reducing CD4 T cell infection. Inhibition of which of the following steps of HIV infection is the most likely therapeutic effect of this experimental drug?
Attachment to host CD4 T-cells
Fusion and entry of HIV into host CD4 T cells are mediated by the HIV envelope glycoprotein ___
41
A 4-month-old boy is brought to the physician because of a painful lesion on his right leg. Yesterday, he received all of his scheduled childhood immunizations, including the second dose of the diphtheria, tetanus, and acellular pertussis vaccine, which was administered in the right quadriceps. Physical examination shows a 2-cm ulcer with surrounding induration over the right anterolateral thigh. A skin biopsy of the lesion shows localized edema, skin necrosis, neutrophilic infiltration, and complement deposition. Which of the following is the most likely cause of his symptoms?
Arthus reaction
A rare, localized, type III hypersensitivity reaction characterized by immune complex deposition in the walls of dermal blood vessels.
A 60-year-old man comes to the office because of an 8-month history of cough, night sweats, shortness of breath, and fatigue. He has also had a 9-kg (19.8-lb) weight loss during this time. He appears pale. Abdominal examination shows hepatosplenomegaly. His leukocyte count is 80,000/mm3 and his leukocyte alkaline phosphatase level is increased. A peripheral blood smear shows > 82% neutrophils with band forms and immature and mature neutrophil precursors. An x-ray of the chest shows a 9-mm right hilar nodule. Which of the following is the most likely cause of this patient’s laboratory findings
A leukemoid reaction is characterized by profound leukocytosis with a proportionate increase in all elements of the myeloid lineage (neutrophils, immature and mature precursors) and elevated leukocyte alkaline phosphatase (LAP), as seen in this patient.
This patient presents with recurring respiratory infections, lymphadenopathy, and inflammatory, pustular lesions, starting at a very young age. Together, these features suggest impaired functioning of phagocytic cells, making him especially susceptible to infection with catalase-positive organisms (e.g., S. aureus, E. coli, Aspergillus).
Defective NADPH oxidase
The NADPH oxidase enzyme is responsible for the respiratory burst (oxidative burst) within phagolysosomes, a component of phagocytic cells, which causes a rapid release of reactive oxygen species (ROS) that can destroy bacteria. In patients with defective NADPH oxidase, also known as chronic granulomatous disease (CGD), this reaction does not occur.
This patient’s symptoms, together with his recent travel history, the findings of the physical examination, and serum studies (especially anti-HAV antibodies) suggest acute infection with hepatitis A virus (HAV). Virus-infected cells produce Interferon α and Interferon β, which upregulate MHC I expression to facilitate the recognition and destruction of infected cells. They also downregulate protein synthesis to prevent viral replication. This process also results in…
Increased breakdown of intracellular RNA
Besides promoting the expression of MHC class I proteins on the surface of virus-infected cells, interferon α and interferon β induce the activation of various enzymes that promote the antiviral state of the cell, including ribonuclease L. Ribonuclease L is an enzyme that mediates the degradation of cellular and viral RNA and thereby inhibits viral protein synthesis.
A 22-year-old man comes to the physician because of abdominal pain, diarrhea, and weight loss that started after a recent backpacking trip in Southeast Asia. He does not smoke or drink alcohol. His leukocyte count is 7,500/mm3 (61% segmented neutrophils, 13% eosinophils, and 26% lymphocytes). Stool microscopy shows rhabditiform larvae (Strongyloides stercoralis). This patient is most likely to develop which of the following?
Perianal serpiginous rash
Strongyloides stercoralis is a nematode endemic to Southeast Asia that is transmitted via larval penetration of intact skin (usually when bare feet come into contact with contaminated soil).
This patient presents with the thumbprint sign (thickening of the epiglottis) on x-ray of the neck as well as classic clinical features (dysphagia, drooling, distress) of acute epiglottitis due to Haemophilus influenzae infection.
The drug of choice for H. influenzae prophylaxis is rifampin, what is its mode of action?
Inhibition of DNA-dependent RNA-polymerase
Inhibition of prokaryotic DNA-dependent RNA polymerase is the mechanism of rifampin, the drug of choice for prophylaxis for Haemophilus influenzae.
A 2-month-old boy is brought to the pediatrician for a routine check-up. His mother says he is feeding well and has no concerns. He is at the 85th percentile for height and 82nd percentile for weight. Immunizations are up-to-date. Results of serum hepatitis B surface IgG antibody testing are positive. Which of the following best explains this patient’s hepatitis B virus status
Passive Immunity
IgG is the most common type of antibody and can indicate prior infection or immunization.
Recurrent infections (bacterial and fungal), failure to thrive, absent tonsils, and absent thymus shadow on x-ray suggest severe combined immunodeficiency (SCID). It also shows
Decreased circulating T cells
This patient’s severe combined immunodeficiency (SCID) is most likely due to an autosomal recessive adenosine deaminase deficiency (the second most common cause of SCID), which results in disrupted purine metabolism and accumulation of metabolites (including deoxyadenosine and dATP) that are toxic to maturing lymphocytes.
Arthritis, fatigue, discoid rash, and oral ulcers are suggestive of systemic lupus erythematosus (SLE). This patient’s history of unprovoked deep vein thromboses (DVTs) should raise concern for antiphospholipid syndrome (APS). They also present
Rapid plasma reagin test (RPR) is a nonspecific screening test for syphilis that detects anticardiolipin antibodies.
Two weeks after undergoing an allogeneic skin graft procedure for extensive full-thickness burns involving his left leg, a 41-year-old man develops redness and swelling over the graft site. He has not had any fevers or chills. His temperature is 36°C (96.8°F). Physical examination of the left lower leg shows well-demarcated erythema and edema (acite graft rejection) around the skin graft site. The graft site is minimally tender and there is no exudate. Which of the following is the most likely underlying mechanism of this patient’s skin condition?
Th1 cell-induced macrophage activation is responsible for this patient’s acute graft rejection. This type IV hypersensitivity reaction is triggered by foreign antigens from the allogeneic skin graft, which incite host T-cell sensitization
