Immune Responses to Extracellular and Intracellular Bacteria Can Differ

Infection by extracellular bacteria induces production of humoral antibodies, which are ordinarily secreted by plasma cells in regional lymph nodes and the submucosa of the respiratory and gastrointestinal tracts. The humoral immune response is the main protective response against extracellular bacteria. The antibodies act in several ways to protect the host from the invading organisms, including removal of the bacteria and inactivation of bacterial toxins (Figure 17-8). Extracellular bacteria can be pathogenic because they induce a localized inflammatory response or because they produce toxins. The toxins, endotoxin or exotoxin, can be cytotoxic but also may cause pathogenesis in other ways. An excellent example of this is the toxin produced by diphtheria, which exerts a toxic effect on the cell by blocking protein synthesis. Endotoxins, such as lipopolysaccharides (LPS), are generally components of bacterial cell walls, while exotoxins, such as diphtheria toxin, are secreted by the bacteria.

Antibody that binds to accessible antigens on the surface of a bacterium can, together with the C3b component of complement, act as an opsonin that increases phagocytosis and thus clearance of the bacterium (see Figure 17-8). In the case of some bacteria—notably, the gram-negative organisms—complement activation can lead directly to lysis of the organism. Antibody-mediated activation of the complement system can also induce localized production of immune effector molecules that help to develop an amplified and more effective inflammatory response. For example, the complement split products C3a, C4a, and C5a act as anaphy-latoxins, inducing local mast-cell degranulation and thus vasodilation and the extravasation of lymphocytes and neu-trophils from the blood into tissue space (see Figure 17-8). Other complement split products serve as chemotactic factors for neutrophils and macrophages, thereby contributing to the buildup of phagocytic cells at the site of infection. Antibody to a bacteria toxin may bind to the toxin and neutralize it; the antibody-toxin complexes are then cleared by phagocytic cells in the same manner as any other antigen-antibody complex.

While innate immunity is not very effective against intra-cellular bacterial pathogens, intracellular bacteria can activate NK cells, which, in turn, provide an early defense against these bacteria. Intracellular bacterial infections tend to induce a cell-mediated immune response, specifically, delayed-type hypersensitivity. In this response, cytokines secreted by CD4+ T cells are important—notably IFN-7, which activates macrophages to kill ingested pathogens more effectively (see Figure 14-15).

Was this article helpful?

0 -1
How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


  • Kimberly
    Can extracellular bacteria act as intracellular?
    8 years ago
  • kevin
    Which innate response to extracellular bacteria?
    2 years ago
  • michael
    Which immune system work on extracellular bacterial?
    2 years ago
  • Hugo
    How does immune response to extracellular and intracellular bacteria differ?
    1 year ago
  • Tomi
    How immune rsponce to exrta cellular ognanism differ from immune rsponce to inta cellualr organism?
    1 year ago
  • kaj
    How the adaptive immune response to extracellular bacterial pathogen?
    9 months ago
  • genet
    Why does your immune system target intracellular and extracellular substances?
    7 months ago
  • mirabella
    How does antobdy work against extracellular bacteria?
    7 months ago
  • peter
    Does the immune response differ for extra and intracellular bacteria?
    5 months ago
  • Bisrat
    How does an immune response to extracellular bacteria differ from one against viruses?
    4 months ago
  • Fergus
    How do amtibiotics act intra or extra cellular?
    3 months ago
  • Barbara
    How does the body respond to intercellular bacterial infectiopn?
    1 month ago
  • Bellisima
    How would you kill an intracellular vs extracellular pathogen?
    1 month ago
    Do the cells protect against infection intercellular or extracellular?
    1 month ago
  • james
    Which antibodies help intracellular infection vs extra cellular infection?
    1 month ago
  • adalgisa
    How the immune system responds to and clears n extracellular bacterial infection?
    1 month ago

Post a comment