## Target Cells of M. leprae **Key Point:** M. leprae is an obligate intracellular pathogen with a marked tropism for peripheral nerve Schwann cells and tissue macrophages, which are the primary sites of bacterial multiplication and persistence. ### Cellular Tropism M. leprae preferentially colonizes: - **Schwann cells** — the most characteristic feature; bacteria accumulate in the cytoplasm and cause demyelination and nerve damage - **Macrophages** — especially in skin and subcutaneous tissues; the bacilli survive within phagolysosomes by inhibiting fusion and acidification - **Fibroblasts** — secondary involvement in granulomas ### Clinical Correlation The predilection for Schwann cells explains why leprosy manifests as: - Peripheral nerve thickening and palpability - Nerve damage leading to anesthesia and motor weakness - Characteristic distribution along cooler peripheral nerves (lower temperature preference) **High-Yield:** The combination of Schwann cell and macrophage tropism is pathognomonic for M. leprae and distinguishes it from other mycobacteria, which primarily target macrophages alone. **Clinical Pearl:** Nerve involvement is the hallmark of leprosy and occurs earlier and more prominently than in tuberculosis, making neurological examination critical in diagnosis. [cite:Park 26e Ch 32]
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