TB infects which cell
First, I need to figure out the correct answer. Tuberculosis (TB) is caused by Mycobacterium tuberculosis. The primary cells it infects are macrophages. Macrophages are part of the innate immune system and are the first line of defense. TB bacteria are phagocytosed by macrophages but can survive inside them by preventing phagosome-lysosome fusion. So the correct answer is likely macrophages.
Now, the core concept here is the interaction between M. tuberculosis and immune cells. The explanation should mention how TB evades the immune response by living inside macrophages.
Next, the why correct answer is right section needs to detail the mechanism. TB bacteria are engulfed by alveolar macrophages in the lungs. They inhibit the fusion of phagosomes with lysosomes, allowing them to replicate intracellularly. They also modulate the host's immune response, leading to granuloma formation.
For the wrong options, common distractors might include other immune cells like neutrophils, dendritic cells, or T-cells. Need to explain why those are incorrect. For example, neutrophils are more involved in acute infections, dendritic cells present antigens but aren't the primary site of TB replication, and T-cells are part of the adaptive response rather than the initial infection site.
Clinical pearl could be that TB's ability to survive in macrophages is key to its chronic nature and latency. Also, the role of granulomas in containing the infection but not eliminating it.
I need to ensure all sections are covered concisely, using precise terminology. Check character count to stay within 2500. Make sure each section is clear and the explanation is thorough but not too lengthy. Also, structure each part with the required bold labels and avoid markdown headings as specified.
**Core Concept**
Tuberculosis (TB), caused by *Mycobacterium tuberculosis*, primarily infects **macrophages**. This intracellular pathogen exploits phagocytic cells of the innate immune system to evade destruction and establish chronic infection.
**Why the Correct Answer is Right**
*M. tuberculosis* is phagocytosed by alveolar macrophages in the lungs. It inhibits phagosome-lysosome fusion, preventing acidification and degradation. The bacteria then replicate within the macrophage, inducing granuloma formation with multinucleated giant cells (Langhans type) and fibroblasts. This intracellular survival mechanism allows TB to persist for decades, often reactivating when immunity wanes.
**Why Each Wrong Option is Incorrect**
**Option A: Neutrophils** – Neutrophils are short-lived phagocytes involved in acute inflammation, not TB’s chronic intracellular survival.
**Option B: Dendritic cells** – While dendritic cells phagocytose TB, they primarily act as antigen-presenting cells, not the primary replicative niche.
**Option C: T-cells** – T-cells (e.g., CD4+ Th1 cells) are part of