Immune Mechanisms Against Extracellular Pathogens


Extracellular pathogens replicate and/or persist on mucosal surfaces or in host tissues outside host cells and may rapidly spread or establish an infection. In this habitat, however, they have to fight against several humoral (e.g. defensins, lactoferrin, antibodies) and cellular (phagocytes, T cells) immune defence mechanisms.

Keywords: extracellular; pathogen; immunity; humoral; cellular

Figure 1.

Pyogenic infections caused by an extracellular bacterial pathogen in mice. (a) Granuloma‐like lesion (arrows) composed of mononuclear cells in the liver 3 days after bacterial infection. Such lesions typically occur in the early phase of infection in the liver, and may also occur upon infection with intracellular bacteria. (b) Microabscess (arrows) composed of polymorphonuclear leucocytes in the liver 5 days postinfection with a bacterial pathogen. (c) Abscess (necrotic centre indicated by an asterisk) in the spleen 7 days postinfection. The abscess is demarcated by a border (arrows), exterior to which is normal spleen tissue (right). (d) Necrotic lesion (indicated by an asterisk) rather than classical abscess in the liver of a T cell‐deficient mouse upon infection with an extracellular bacterial pathogen, suggesting that T cells are required for formation of abscesses.



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Further Reading

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Autenrieth, Ingo B, Hein, Joachim, and Schulte, Ralf(Apr 2001) Immune Mechanisms Against Extracellular Pathogens. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0000479]