تسجيل الدخول

تسجيل

Neutralization of Microbes and Microbial Toxins

المؤلف:  Abbas, A. K., Lichtman, A. H., Pillai, S., & Henrickson, S. E.

المصدر:  Cellular and Molecular Immunology (2026)

الجزء والصفحة:  11E, P295-296

2026-09-06

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 Antibodies against microbes and microbial toxins block the binding of these microbes and toxins to cellular receptors (Fig. 1). In this way, antibodies can neutralize (i.e., inhibit) the infectivity of microbes as well as the potential injurious effects of microbial toxins. Many microbes enter host cells by the binding of microbial surface molecules to membrane proteins or lipids on the surface of host cells. For example, influenza viruses use their envelope hemagglutinin to infect respiratory epithelial cells, and gram-negative bacteria use adhesins in their pili to attach to and infect a variety of host cells. Antibodies that bind to these microbial structures interfere with the ability of the microbes to interact with cellular receptors by means of steric hindrance and thus prevent infection. Many microbial tox ins mediate their pathologic effects also by binding to specific cellular receptors. For instance, tetanus toxin binds to receptors in the motor end plate of neuromuscular junctions and inhibits neuromuscular transmission, which leads to paralysis, and diphtheria toxin binds to cellular receptors and enters various cells, where it inhibits protein synthesis. Antibodies against such toxins block the interactions of toxins with host cells and thus prevent the toxins from causing tissue injury and disease. In the lumen of mucosal organs (the gut and airways), aggregation or agglutination of microbes by IgA antibodies can reduce the infectivity of the pathogens, trap them in mucus, and facilitate their clearance by peristalsis or respiration. In some cases, antibodies may bind to a microbe and induce conformational changes in surface molecules that prevent the microbe from interacting with cellular receptors. Such interactions have been observed for antibodies against certain viruses and are examples of the allosteric effects of antibodies.

Fig1. Neutralization of microbes and toxins by antibodies. (A) Antibodies prevent the binding of microbes to cells and thus block the ability of the microbes to infect host cells. (B) Antibodies inhibit the spread of microbes from an infected cell to an adjacent uninfected cell. (C) Antibodies block the binding of toxins to cells and thus inhibit the pathologic effects of the toxins.

Antibody-mediated neutralization of microbes and toxins requires only the antigen-binding regions of the antibodies. Therefore, such neutralization may be mediated by antibodies of any class in the circulation and in mucosal secretions and can experimentally or therapeutically also be mediated by Fab or F(ab)2 fragments of specific antibodies, which lack the Fc regions of the heavy chains. Neutralizing antibodies are mainly of the IgG class in the blood and most peripheral tissues and the IgA class at mucosal sites. The most effective neutralizing antibodies are those with high affinities for their antigens. High-affinity antibodies are produced by the process of affinity maturation. Many prophylactic vaccines work by stimulating the production of high-affinity neutralizing anti bodies (see Table 1). A mechanism that microbes have developed to evade host immunity is to mutate the genes encoding surface antigens that are the targets of neutralizing antibodies.

Table1. Examples of Vaccine-Induced Humoral Immunity