Biology · MU Sofia

48. Functions of antibodies.

Covers the direct actions of antibodies, such as neutralising toxins with antitoxins and blocking pathogen attachment, followed by indirect roles that recruit complement, opsonisation and inflammation. It then describes the roles of each immunoglobulin class, natural antibodies, and the Type I to III hypersensitivity reactions, with four mnemonics summarising the functions. The note closes with an introduction to T cell receptors and their structure.

Inside: 10 sections · 3 labelled pictures · 10 flashcards · 10 min

Topic 49 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 10 sections, about 1,317 words (10 min of reading), with 10 flashcards.

In this note

  1. Functions of antibodies
  2. Understanding the Multifaceted Functions of Antibodies
  3. Direct Functions: Neutralizing and Blocking Threats
  4. Indirect Functions: Enlisting the Innate Immune Army
  5. Complement Activation via the Classical Pathway
  6. Specialized Roles of Different Antibody Classes
  7. Natural Antibodies: Born Ready
  8. When Antibodies Go Wrong: Hypersensitivity Reactions
  9. MNEMONICS
  10. Molecules of cell-mediated immunity.

Understanding the Multifaceted Functions of Antibodies

Antibodies are remarkable protein molecules produced by the immune system to recognize and bind antigens—foreign substances like bacteria, viruses, and toxins. But their power doesn’t lie in destroying pathogens directly. Rather, they serve as highly specialized connectors—linking foreign invaders with the innate immune system and orchestrating a cascade of defensive actions.

Direct Functions: Neutralizing and Blocking Threats

Antibodies exert direct effects simply by attaching themselves to their targets. This can neutralize toxins or prevent microbes from gaining a foothold in the body.

Neutralizing Toxins

Many bacterial and animal toxins are proteins that can be neutralized by specific antibodies called antitoxins. These antibodies block the toxic effects by binding to the active sites on the toxin molecules, effectively disabling them.

  • Antitoxins can be introduced through:
  • Passive immunization (e.g., injecting antiserum from immunized animals)
  • Active immunization using toxoids (inactivated toxins that stimulate the immune system to produce its own antibodies), as seen in vaccines like diphtheria or tetanus.
  • This method is also life-saving in emergencies like snake bites and scorpion stings, where engineered antibodies or animal-derived antisera are used to neutralize venom.

Preventing Pathogen Adherence

By coating the surfaces of bacteria or viruses, antibodies make it harder for them to attach to our cells. This is especially important at vulnerable mucosal surfaces.

  • IgA plays a crucial role here, being secreted in tears, saliva, mucus, and other bodily fluids. It blocks pathogens before they can attach to epithelial surfaces.
  • IgG and IgM also protect internal tissues by preventing microbes from binding to blood vessels and organs.

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