Immunodepression

Question 1

T-cell Deficiency (Cell-mediated immunity)

Answer 1

Common in: HIV/AIDS, DiGeorge syndrome, immunosuppressants (e.g., calcineurin inhibitors)
• Susceptible to:
• Viral infections (CMV, HSV, VZV, JC virus → PML)
• Fungal infections (Candida, Pneumocystis jirovecii)
• Intracellular bacteria (Mycobacteria, Salmonella)

Tip: Opportunistic infections (e.g., PCP pneumonia, esophageal Candida, CMV retinitis) often point to CD4+ T cell loss (e.g., AIDS).

Question 2

B-cell Deficiency (Humoral immunity)

Answer 2

Seen in: X-linked agammaglobulinemia, CVID, rituximab therapy
• Susceptible to:
• Encapsulated bacteria: SHiNE SKiS → Strep pneumo, H. influenzae, Neisseria, E. coli, Salmonella, Klebsiella, Strep group B
• Enteroviruses (e.g., echovirus)
• Giardia (due to IgA deficiency)

Tip: Recurrent sinopulmonary infections + no tonsils = suspect X-linked agammaglobulinemia.

Question 3

Neutrophil Dysfunction

Answer 3

Seen in: Chronic granulomatous disease (CGD), chemotherapy, diabetes
• Susceptible to:
• Catalase-positive organisms: S. aureus, Pseudomonas, Serratia, Nocardia, Aspergillus
• Fungal infections: Aspergillus, Candida

Tip: Recurrent skin abscesses or granulomas = think CGD.

Question 4

Complement Deficiency

Answer 4

C3 deficiency: Recurrent pyogenic infections
• MAC (C5–C9) deficiency: Neisseria infections

Tip: Young patient with recurrent Neisseria meningitis = screen for terminal complement deficiency.

Question 5

Splenic Dysfunction or Asplenia

Answer 5

Causes: Sickle cell disease, splenectomy
• At risk for encapsulated bacteria (same SHiNE SKiS list)
• Need vaccinations: Pneumococcus, H. flu, Meningococcus

Tip: Asplenic patients → increased risk of sepsis from minor infections.

Question 6

A. HIV/AIDS

Answer 6

CD4 <200 → PCP (Pneumocystis jirovecii pneumonia)
• CD4 <100 → Toxoplasma gondii, Cryptococcus
• CD4 <50 → CMV, Mycobacterium avium complex (MAC)

Tip:
• PCP: Dry cough, dyspnea, bilateral ground-glass opacities
• CMV retinitis: “Pizza pie” fundus, painless vision loss

Question 7

Transplant or Cancer Patients (On Immunosuppressants)

Answer 7

Opportunistic infections: CMV, EBV, Aspergillus, BK virus
• Reactivation of latent TB or hepatitis

Tip: Neutropenic fever is a medical emergency—start broad-spectrum antibiotics immediately (e.g., cefepime).

Question 8

Diabetics

Answer 8

Mucormycosis, Candida, bacterial infections (especially skin), UTIs

Tip: Diabetic ketoacidosis + sinus symptoms = think Mucor or Rhizopus.

Question 9

Corticosteroids use

Answer 9

↓ Neutrophil adhesion, ↓ T and B cell function
• Risk for fungal infections, reactivation of TB, poor wound healing

Tip: Look for Cushingoid features or long-term steroid use → increased risk for infections and delayed healing.

Question 10

USMLE Step 1 Tips

Answer 10

Immunodeficiency
Most common infections

T-cell defects
PCP, CMV, Candida, viruses

B-cell defects
Encapsulated bacteria, Giardia

Neutrophil defects
Staph aureus, Aspergillus

Complement
Neisseria species

Asplenia
Encapsulated bacteria

Tips for Recognizing Immunodepression in Vignettes
• Clues to immune status: HIV+, chemotherapy, transplant, steroids, diabetes, age (very young/old), genetic syndromes
• Pay attention to the infection type: Fungal = T-cell; recurrent pneumonia = B-cell; abscesses = neutrophils
• Suspect reactivation (e.g., TB, herpes, VZV) when immune system is suppressed