16. Primary tuberculosis complex. Tuberculous brochoadenitis

What is primary TB?

• Type of TB which occurs after very first contact with Mycobacterium species
• Patient is sick from TB for the first time
• More common in children, adolescents and young adults
• Spreads via blood and lymph!

Pathogenesis

• Infection occurs when person inhales droplet nuclei containing tubercle bacilli that reach the alveoli of the lungs
• The first contact of the Mycobacterium organism with a host leads to manifestations known as primary tuberculosis.
• This primary TB is usually localized to the middle portion of the lungs, and this is known as the Ghon focus of primary TB.
• In most infected individuals, the Ghon focus enters a state of latency. This state is known as latent tuberculosis
• Tuberculosis is a classic example of a cell-mediated delayed type IV hypersensitivity reaction:
• By stimulating the immune cells (the helper T-Lymphocyte, CD4+ cells), Mycobacterium tuberculosis induces the recruitment and activation of tissue macrophages. This process is enhanced and sustained by the production of cytokines, especially interferon-gamma.
• Two main changes involving macrophages occur during this process, namely, the formation of multinucleated giant cells and the formation of epithelioid cells
• The aggregation of giant cells surrounding the Mycobacterium particle and the surrounding lymphocytes and other cells is known as a granuloma
• In addition to interferon-gamma (IFN-gamma), the following cytokines play important roles in the formation of a tuberculosis granuloma, Interleukin-4 (IL-4), Interleukin-6 (IL-6), and tumor necrotic factor-alpha (TNF-alpha).
• The appearance of the granuloma in tuberculosis has been described as caseous or cheese-like on gross examination. This is principally explained by the rich mycolic acid content of the mycobacterium cell wall