What is the pathogenesis of tuberculosis?

Pathogenesis of Tuberculosis (TB)

Tuberculosis is caused by the bacterium Mycobacterium tuberculosis. Its pathogenesis is primarily based on the host immune response to the infection, which leads to the formation of granulomas — a hallmark of TB. The bacteria can persist in a latent state or cause active disease, depending on the host’s immunity.

Step-by-Step Pathogenesis

1. Inhalation of Bacilli

  • Infection begins when M. tuberculosis is inhaled in airborne droplets.

  • The bacilli reach the alveoli of the lungs.

2. Phagocytosis by Alveolar Macrophages

  • Alveolar macrophages engulf the bacilli.

  • M. tuberculosis inhibits phagosome-lysosome fusion, allowing it to survive and replicate inside the macrophage.

3. Immune Activation (within 2–3 weeks)

  • Infected macrophages release cytokines (e.g., IL-12) and present TB antigens to CD4+ T-helper cells (Th1).

  • Th1 cells release interferon-gamma (IFN-γ), activating macrophages to kill ingested bacilli.

 4. Granuloma Formation

  • Activated macrophages transform into:

    • Epithelioid cells (specialized macrophages)

    • Multinucleated giant cells

  • These cells are surrounded by T cells, B cells, and fibroblasts, forming a granuloma to contain the infection.

  • The granuloma may undergo caseous necrosis —the central area becomes cheese-like.

 5. Latent vs. Active TB

Latent TB Active TB
Strong immune response contains the bacilli Weakened immunity fails to control infection
Bacilli remain dormant in granulomas Granulomas break down, bacilli spread
No symptoms, not contagious Symptoms present, highly contagious

6. Reactivation (Secondary TB)

  • Occurs when immunity wanes (e.g., HIV, malnutrition, aging)

  • Commonly affects lung apices (high oxygen tension)

  • Leads to cavitary lesions, which allow bacilli to enter the airways and be transmitted

7. Disseminated (Miliary) TB

  • If bacilli enter the bloodstream, they spread to multiple organs (liver, spleen, bone marrow, meninges), causing miliary TB (tiny millet-seed-like lesions)

Summary Table

Step Event
1 Inhalation of M. tuberculosis
2 Phagocytosis by macrophages
3 Immune activation → IFN-γ release
4 Granuloma formation with caseous necrosis
5 Latency or active disease depending on immunity
6 Possible reactivation or dissemination


Comments

Post a Comment

Popular posts from this blog

What is a dpt program?

 🩺 What is the DPT Program?  If you've ever been fascinated by how the human body moves and heals — and want a career that blends science, care, and impact — then a  Doctor of Physical Therapy (DPT)  program might be your perfect match. Whether you're a high school student exploring health careers, a college graduate looking to specialize, or just curious about physical therapy education, this article will break down  what the DPT program is , what it includes, and how it prepares you to become a licensed physical therapist. 🧠 What is a DPT Program? The  Doctor of Physical Therapy (DPT)  program is a  postgraduate professional doctorate  designed to train students to become licensed  physical therapists (PTs) . It’s the  entry-level requirement  for anyone who wants to practice as a PT in many countries, including the United States. This degree focuses on: Movement science Patient rehabilitation Injury prevention Manual thera...
Read more

What is osteogenesis imperfecta?

Image
What is Osteogenesis Imperfecta? | Causes, Types, Symptoms & Treatment Osteogenesis Imperfecta (OI) , also known as “brittle bone disease,” is a rare genetic disorder characterized by fragile bones that break easily , often with little or no trauma. It affects the production of collagen , a key protein that provides strength and structure to bones and connective tissues.  What is Osteogenesis Imperfecta? Osteogenesis Imperfecta is a hereditary connective tissue disorder . It primarily affects the bones but may also involve the teeth, skin, ligaments, and eyes . The condition is caused by mutations in genes—mostly COL1A1 or COL1A2 —that control the production of type I collagen . As a result, bones become brittle, leading to frequent fractures and skeletal deformities.  Types of Osteogenesis Imperfecta  There are at least eight recognized types of OI, varying from mild to severe. Here's a simplified breakdown: Type Description Severity Type I Most...
Read more

what is brain encephalitis?

Image
Brain Encephalitis: Causes, Symptoms, Diagnosis & Treatment Encephalitis is a serious and potentially life-threatening medical condition characterized by inflammation of the brain . It is often caused by a viral infection  but may also occur due to autoimmune reactions, bacteria, or other pathogens. If not treated promptly, encephalitis can lead to severe neurological complications.  What is Brain Encephalitis? Encephalitis is the inflammation of brain tissue. The inflammation causes the brain to swell, which can interfere with normal brain function and lead to a wide range of neurological symptoms. It can be classified as: Primary encephalitis : Direct viral infection of the brain. Secondary encephalitis : An immune response following an infection elsewhere in the body. Causes of Encephalitis 1. Viral Infections (Most Common Cause) Herpes Simplex Virus (most common and severe) Enteroviruses Varicella-zoster virus (chickenpox) Measles, mumps, r...
Read more