5.4
Gastrite II: Fisiopatologia
La fisiopatologia della gastrite inizia con la colonizzazione del rivestimento gastrico da parte di Helicobacter pylori (H. pylori). Questo batterio s…
La gastrite indotta da H. pylori inizia con la trasmissione batterica alla mucosa gastrica, comunemente tramite cibo o acqua contaminati.
H. pylori sopravvive all'ambiente acido dello stomaco producendo ureasi. L'urease idrolizza l'urea in ammoniaca, neutralizzando localmente l'acido gastrico e creando un microambiente protettivo.
Il batterio utilizza poi i suoi flagelli e gli enzimi mucolitici per penetrare lo strato mucoso e aderire alle cellule epiteliali gastrica.
Questo attaccamento attiva una risposta immunitaria. Macrofagi e cellule T cercano di eliminare l'infezione, ma H. pylori fa sì che le cellule epiteliali esprimano il ligando 1 della morte programmata, o PD-L1. PD-L1 si lega a PD-1 sulle cellule T, inviando segnali inibitori che ne riducono l'attività e permettono l'evasione immunitaria.
Contemporaneamente, H. pylori innesca la secrezione di interleuchina-8, attirando neutrofili e amplificando l'infiammazione.
H. pylori inietta fattori di virulenza come il gene associato alla citotossina A nelle cellule ospiti. Questo interrompe la segnalazione cellulare e le giunzioni strette, contribuendo a infiammazioni prolungate e gastrite.
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Q1: How does H. pylori survive in the stomach's acidic environment?
H. pylori produces urease, an enzyme that breaks down urea into ammonia and carbon dioxide. The ammonia neutralizes gastric acid locally, creating a protective microenvironment where the bacterium can survive and establish infection in the stomach lining.
Q2: What role does urease play in H. pylori colonization?
Urease hydrolyzes urea into ammonia, which buffers the surrounding gastric acid and allows H. pylori to survive long enough to penetrate the mucus layer. This enzyme is essential for the bacterium's initial colonization and establishment in the stomach.
Q3: How does H. pylori evade the immune system?
H. pylori induces infected gastric epithelial cells to express PD-L1, which binds to PD-1 receptors on T-cells and suppresses their activity. This immune evasion mechanism allows the bacterium to establish chronic colonization despite the host's immune response.
Q4: What is the relationship between H. pylori infection and intestinal metaplasia?
Persistent H. pylori infection causes chronic inflammation that damages gastric epithelial cells and leads to mucosal atrophy. Over time, this prolonged epithelial damage may progress to intestinal metaplasia, a precancerous change that significantly increases the risk of gastric carcinoma.
Q5: How does CagA virulence factor contribute to gastritis pathophysiology?
H. pylori injects CagA into host cells through a type IV secretion system, where it disrupts cell signaling pathways and tight junctions. This virulence factor promotes inflammation, cellular damage, and increases the risk of gastric malignancy during chronic infection.
Q6: What mechanisms allow H. pylori to penetrate the gastric mucus layer?
H. pylori uses flagella for motility and secretes mucinases to degrade the mucus layer protecting the stomach wall. These adaptations enable the bacterium to reach and adhere to underlying gastric epithelial cells, initiating the inflammatory cascade.
Q7: How does interleukin-8 amplify inflammation during H. pylori gastritis?
Infected gastric epithelial cells release interleukin-8, a chemokine that recruits immune cells such as neutrophils to the infection site. This amplifies the inflammatory response, contributing to prolonged inflammation and tissue damage characteristic of H. pylori-induced gastritis.