A 57-year-old woman with autosomal dominant polycystic kidney disease develops end-stage renal disease and undergoes deceased-donor kidney transplantation.  During the operation, the surgeon notices that the graft becomes cyanotic and mottled soon after its blood vessels are connected with those of the recipient.  Blood flow to the graft ceases, and no urine is produced.  Which of the following best explains the findings observed by the surgeon?

A 7-month-old boy is brought to the physician by his parents due to irritability and white patches in his mouth.  His past medical history is significant for 3 episodes of otitis media and 2 episodes of bronchiolitis that have required hospitalization.  He also has a history of chronic loose stools.  The child is small for his age and ill-appearing.  Head and neck examination shows white patches consistent with oral candidiasis but is otherwise normal.  Auscultation of the lungs shows expiratory wheezing.  Cardiac examination is within normal limits.  Laboratory results are as follows:

Serum protein electrophoresis shows a very low gamma globulin level.  Chest x-ray reveals an absent thymic shadow.  Which of the following is the most likely diagnosis?

A 7-year-old boy is evaluated for a foot wound.  He sustained a splinter injury to his left foot while playing in the yard several days ago and has continued to have purulent drainage from the wound.  The patient has no significant medical history and is up to date with all recommended vaccinations.  Wound examination reveals a small retained foreign body with surrounding necrotic tissue and pus.  Anaerobic culture of the wound swab grows thin, gram-positive rods with terminal spore, which is biochemically identified as Clostridium tetani.  Which of the following most likely protected this patient from developing neurological symptoms of the infection?

A 4-year-old male is exposed to latex gloves during a minor surgical procedure and is subsequently found to produce anti-latex IgM antibodies.  Several months later he develops a severe allergic reaction to latex and is found to have a high level of serum anti-latex IgE antibodies.  Which of the following cytokines is most likely responsible for this anti-latex antibody isotype change?

Foreign antigen recognition at the cell surface by cytotoxic T-lymphocytes stimulates a response that results in rapid cell death.  Which of the following act as effectors of this response?

A 5-month-old boy with chronic diarrhea and failure to thrive is found to have a low blood T-lymphocyte count and severely decreased serum immunoglobulin.  After thorough evaluation, an experimental treatment is proposed to his parents.  The therapy consists of infecting the patient’s cells with a retroviral vector containing the gene for a protein that is deficient in this patient.  Which of the following proteins is most likely coded by this gene?

A 71-year-old man with chronic obstructive pulmonary disease (COPD) is hospitalized due to shortness of breath and wheezing.  The patient is treated with bronchodilators and systemic corticosteroids for acute COPD exacerbation.  His symptoms improve over the next 2 days.  Before being discharged, an intramuscular vaccine containing inactivated viral components, which he normally receives annually, is administered.  Several weeks later, the patient comes in close contact with an individual infected with the same virus contained in the vaccine.  Which of the following is most likely to occur in this patient as a result of the vaccination?

A newborn girl is admitted to the neonatal intensive care unit with jaundice, hepatomegaly, and generalized edema.  She was born by vaginal delivery to a 32-year-old woman, gravida 2, para 2, who received minimal prenatal care.  The infant’s laboratory results show a hemoglobin level of 6 g/dL and a positive direct Coombs test.  A peripheral blood smear shows many nucleated erythrocytes.  The infant has significant respiratory distress due to pleural effusions and ascites and dies soon after birth.  Autopsy shows areas of extramedullary hematopoiesis in many tissues.  Which of the following is the most likely cause of this patient’s condition?

A 28-year-old woman, gravida 2 para 2, brings her healthy 6-day-old girl to the office for her first well-baby checkup.  The infant was born full-term, with a birth weight of 4.2 kg (9.3 lb) and a length of 51 cm (20 in).  She was discharged from the nursery with no concerns.  Physical examination is normal.  The infant’s blood type is A negative, whereas the mother’s is B negative.  High circulating levels of anti-A antibodies are found in the mother’s blood.  Hemolysis did not occur in the infant because these maternal antibodies are most likely of which class?

On flow cytometric analysis of a sample of fetal thymus, a certain population of cells is identified that is positive for both CD4 and CD8 cell surface antigens.  These cells are best characterized as which of the following cells?

A 24-year-old hospital phlebotomist comes to the occupational health clinic after sustaining a needlestick injury while drawing blood from a hepatitis B–positive patient.  She has no medical history and received the complete hepatitis B vaccination series prior to her hospital employment a year ago.  She is closely monitored over the next 6 months with repeat hepatitis B serologies and does not develop clinical or laboratory evidence of infection.  Which of the following mechanisms most likely explains her immunity?

A 56-year-old man comes to the emergency department due to fever and malaise for the past day.  The patient was recently diagnosed with diffuse large B-cell lymphoma and completed the first cycle of combination chemotherapy 10 days ago.  Temperature is 38.4 C (101.1 F).  Physical examination is unremarkable with the exception of diffuse lymphadenopathy.  The patient is hospitalized, and empiric antibiotics are initiated.  Two days later, blood cultures drawn on admission grow yeast forms with pseudohyphae and demonstrate an ability to form germ tubes.  Which of the following immunodeficiency mechanisms is most likely responsible for the invasiveness of this patient’s infection?

A 52-year-old woman comes to the emergency department with pain and redness affecting her left leg.  The patient’s symptoms began 2 days ago and have progressed to the point where she cannot walk without experiencing severe pain.  Physical examination shows a large, erythematous area with indistinct margins over her left leg.  The area feels hot and indurated and is exquisitely tender.  She is admitted to the hospital for severe left leg cellulitis and is started on intravenous cefazolin.  Several minutes after the infusion is started, she experiences shortness of breath, diffuse itching, and dizziness.  Her blood pressure is 64/38 mm Hg and heart rate is 130/min.  On examination, there is a diffuse erythematous skin rash and bilateral wheezing is heard on lung auscultation.

Item 1 of 2

Which of the following is most likely to be elevated in this patient’s serum as a result of her medication reaction?

Item 2 of 2

The patient’s anaphylactic reaction is determined to be mediated by antigen-specific IgE antibodies attached to high-affinity receptors on the surface of mast cells and basophils.  Which of the following mechanisms is most likely to trigger vasoactive substance release by these cells?

An 18-month-old, partially vaccinated boy is brought to the office for a routine well-child examination.  His parents have elected a delayed schedule for vaccine administration based on personal preferences.  Today, the patient is scheduled to receive the Haemophilus influenzae serotype b (Hib) conjugate vaccine.  The parents are given detailed information about the vaccine, but the mother asks, “Why is ‘tetanus toxoid conjugate’ listed on the package insert?”  She adds that her son already received the diphtheria-tetanus-acellular pertussis (DTaP) vaccine.  The parents request an explanation for the reason the Hib vaccine contains both the capsular polysaccharide of Hib as well as the conjugated tetanus toxoid.  Which of the following best describes the purpose of Hib vaccine conjugation?

A 5-year-old child is brought to the emergency department by his parents for right arm pain.  The patient reports that he was playing hide and seek outside and felt a sharp pain on his arm while hiding in some thick bushes.  His parents suspect that something had stung him.  Physical examination shows an edematous and erythematous plaque with mild central pallor.  A residual stinger, located central to the lesion, is readily extracted.  The physical examination is otherwise not significant.  Which of the following substances is most likely directly responsible for the skin findings observed in this patient?

An infant is born with facial dysmorphia and a cleft palate.  Chest x-ray shows decreased soft tissue density in the right anterior mediastinum.  Cardiac imaging reveals a right-to-left shunt.  The infant experiences frequent and recurrent sinopulmonary infections but never develops appreciable lymphadenopathy.  The cells deficient in this patient’s condition are normally the major constituent of which of the following lymph node regions?

The immune response in a healthy 12-year-old boy is observed after a recurrent bacterial infection.  It is characterized by a rapid increase in pathogen-specific immunoglobulin levels.  The immunoglobulins bound to the bacteria also attach to phagocytic cells (eg, macrophages, neutrophils) to enhance phagocytosis.  Which of the following immunoglobulin regions is most likely involved in interacting with these phagocytic cells?

A 68-year-old man comes to the office for a follow-up appointment.  He has a history of advanced melanoma that is unresectable and resistant to adjuvant regimens.  The patient recently began receiving monoclonal antibody infusions for advanced melanoma.  The monoclonal antibodies block a specific cell surface receptor found on T lymphocytes.  As a result, T cells capable of recognizing tumor antigens have improved ability to destroy cancer cells.  Which of the following cell surface receptors is most likely blocked by the treatment?

A 55-year-old man with end-stage hepatitis C virus infection undergoes orthotopic liver transplantation from a deceased donor.  The patient has no perioperative complications and is discharged from the hospital on appropriate immunosuppressant medications.  One week after the surgery, he develops nausea, vomiting, abdominal pain, and bloody diarrhea.  Physical examination shows a painful maculopapular rash over his neck, back, and extremities that extends to the palms and soles.  Endoscopic evaluation reveals multiple ulcerations of the intestinal mucosa.  Which of the following is the most likely cause of this patient’s current condition?

A 28-year-old primigravid woman comes to the office for a routine prenatal checkup at 28 weeks gestation.  The patient has no concerns and has had an uneventful pregnancy to date.  Physical examination shows a uterine size concordant with ultrasound dates, and fetal cardiac activity is in the normal range.  After reviewing the results of her laboratory evaluations, the physician administers an injection of anti-Rh(D) immunoglobulin.  The administered antibodies most likely belong to which of the following immunoglobulin classes?

Preventive disease specialists working in a developing country are investigating vaccination options to limit the spread of poliomyelitis.  As part of the study, 2 patients are vaccinated against poliomyelitis.  One patient receives an intramuscular inactivated vaccine and the other patient receives a live attenuated oral vaccine.  One month after vaccination, the levels of which of the following poliovirus antibodies will differ the most between these 2 patients?

A research scientist is comparing surface antigens X and Y that come from 2 different viruses.  He obtains antibodies against antigen X from an animal previously exposed to the virus expressing this antigen.  These antibodies are then attached to assay plates.  Next, a fixed quantity of radiolabeled X antigen is added to the plates.  Unlabeled Y antigens are then added in increasing concentrations to each plate, and the plates are washed to remove unbound antigens.  Radioactivity is plotted as a function of Y antigen concentration, as shown in the graph below.

Which of the following best describes the results of this experiment?

A 13-month-old boy is brought to the emergency department due to cough and increased work of breathing.  The patient’s parents immigrated to the United States when he was 6 months old.  He has a history of recurrent otitis media, pneumonia, and thrush as well as chronic diarrhea and failure to thrive.  On physical examination, he is tachypneic and has perioral cyanosis.  A chest radiograph shows bilateral interstitial opacities.  The patient is admitted to the hospital and undergoes bronchoscopy.  Analysis of the bronchoalveolar lavage fluid reveals Pneumocystis jirovecii.

Item 1 of 2

Which of the following is the most likely underlying diagnosis?

Item 2 of 2

Once the patient recovers from his acute illness, Candida antigen injection into his skin reveals no signs of inflammation after 48 hours.  The same test performed in his mother produces 12 mm of skin induration within 48 hours.  Which of the following cells are directly involved in the effector response observed in the mother?

A 4-year-old boy is evaluated due to 4 days of fever and leg pain.  Medical history includes recurrent skin abscesses and lymphadenitis.  A maternal uncle died of recurrent infections during childhood.  The patient is at the 10th percentile for height and weight.  Temperature is 38.3 C (100.9 F).  Examination shows an ill-appearing patient with point tenderness over the right lower tibia.  There are healed incisions over the thighs and neck from prior drainage sites.  Imaging reveals evidence of tibial osteomyelitis.  Blood and bone cultures grow Serratia marcescens.  Evaluation of the patient’s neutrophils by dihydrorhodamine flow cytometry shows an absence of fluorescence.  This patient’s condition is most likely due to impaired activity of which of the following enzymes?

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?

A scientist is interested in the mechanisms by which leukocytes traffic to sites of inflammation and infection.  She finds that endothelial cells increase the expression of certain cell surface molecules in response to cytokines to allow for leukocyte trafficking.  She subsequently creates a knockout mouse that has a deletion in the platelet endothelial cell adhesion molecule 1 (PECAM-1) gene.  The protein product of this gene is mainly localized to specific areas on the endothelial cells.  Absent expression of this gene will most likely affect which of the following neutrophil functions?

An 8-year-old boy is brought to the office due to fever and sore throat for the past several days.  He has had no runny nose or cough.  Temperature is 38.4 C (101.1 F).  Physical examination shows erythematous pharyngeal mucosa with enlarged tonsils covered by exudates.  There are enlarged and tender anterior cervical lymph nodes.  A representative image of one of the enlarged nodes is shown below; the structures indicated by the arrows are increased in size and number.  The predominant cell type within these regions is most likely undergoing which of the following processes?

A 33 year-old female is being followed by her neurologist for her multiple sclerosis.  She was initially diagnosed with relapsing remitting subtype after an episode of visual disturbance and an episode of paralysis.  In her study of autoimmune diseases she encounters the topic of lymphocyte development and comes across a question which she poses to her neurologist during a routine follow-up visit: During the process of T-lymphocyte maturation, T cell receptors of many lymphocytes demonstrate a very high-affinity interaction with MHC molecules expressed on thymic medullary epithelial and dendritic cells.  What process do these lymphocytes undergo at this time?

A 34-year-old electric company worker comes to the physician with a skin rash on his right leg.  He has not eaten any new foods or changed detergents, soaps, or lotions.  On further questioning, the patient recalls that he recently worked on a repair job in an unmaintained, wooded area.  He had atopic dermatitis as a child but no other significant illnesses.  On physical examination, he appears uncomfortable and is constantly scratching his leg.  His lungs are clear bilaterally and his heart sounds are normal.  Examination of his right leg shows the findings in the image below.

Which of the following cells is most responsible for causing the tissue damage seen in this patient?

A 37-year-old man comes to the emergency department because of increasing pain and tenderness in his right forearm.  During a bar brawl 6 days earlier, he sustained a 4-cm laceration through the skin and subcutaneous tissue of his forearm.  Treatment at the time of injury included cleaning and dressing the wound.  Physical examination shows erythema surrounding the wound site and expression of yellow pus when pressure is applied adjacent to the wound.  Which of the following molecules is most likely responsible for causing accumulation of pus over this patient’s wound?

Researchers develop a novel agent to treat extrinsic asthma.  In a clinical trial, patients with moderate to severe asthma treated with this medication experience fewer exacerbations.  They are also found to have lower levels of serum IgE, even after exposure to triggering allergens.  Analysis of genomic DNA shows reduced IgE isotype switching in activated B lymphocytes.  The new medication most likely inhibits which of the following cytokines?