In protein-energy malnutrition, which of the following immune functions is LEAST affected compared to other immune parameters?

Explanation

## Immune Dysfunction in Protein-Energy Malnutrition **Key Point:** PEM causes widespread immunosuppression, but the **complement system remains relatively preserved** compared to cellular and humoral immunity. Cell-mediated immunity and antibody production are severely impaired, while complement levels and function are only mildly affected. ### Hierarchy of Immune Impairment in PEM 1. **Most Severely Affected:** - T-cell count and cell-mediated immunity (CMI) - Thymic atrophy and reduced T-lymphocyte production - Delayed-type hypersensitivity (DTH) is markedly diminished 2. **Moderately Affected:** - Antibody production (IgG, IgA, IgM) - B-cell function and plasma cell differentiation - Neutrophil bactericidal capacity (reduced oxidative burst, impaired chemotaxis) 3. **Least Affected:** - Complement system (C3, C4 levels remain relatively normal) - Complement-mediated opsonization and MAC formation are preserved ### Comparison Table | Immune Component | Status in PEM | Clinical Consequence | |------------------|---------------|----------------------| | **T-cell count** | ↓↓↓ (severe) | Increased susceptibility to intracellular pathogens (TB, fungi, viruses) | | **Antibody production** | ↓↓ (moderate) | Reduced response to vaccines, impaired opsonization | | **Neutrophil function** | ↓↓ (moderate) | Increased bacterial infections, impaired wound healing | | **Complement (C3, C4)** | ↓ or normal (mild) | Relatively preserved complement-mediated lysis | | **Phagocytic capacity** | ↓↓ (moderate) | Reduced killing of ingested organisms | **High-Yield:** The **complement system is the most resilient immune component in PEM**. This is why complement levels (C3, C4) are often used as a marker of nutritional recovery—they normalize relatively quickly with refeeding, whereas T-cell counts take longer to recover. **Clinical Pearl:** A malnourished child with a normal serum C3 level but absent delayed-type hypersensitivity (DTH) to tuberculin or candida antigen is a classic presentation of PEM-induced immunosuppression. **Mnemonic:** **CMI First, Complement Last** — Cell-Mediated Immunity is hit hardest; Complement is least affected.