Passive immunization: immunoglobulins and antitoxins !
- Topic
In passive immunization a person receives ready-made antibodies. They protect at once, but last weeks or months and leave no memory.
Updated 2026-11-01
What it is
Passive immunity means receiving antibodies made by another person or an animal. It can be natural (IgG crossing the placenta, IgA in breast milk) or artificial (human immunoglobulins, hyperimmune globulins, animal antitoxins and monoclonal antibodies). It is used when there is no time to wait for an active response or when the person cannot mount one.
Key facts
- IgG is the only immunoglobulin that crosses the placenta; it protects the newborn for the first months.
- Hyperimmune globulins: against hepatitis B, rabies, tetanus and varicella.
- Horse-derived antitoxins (diphtheria, botulism) and antivenoms neutralize toxins but can cause serum sickness.
- Anti-D immune globulin stops an Rh-negative mother from becoming sensitized to the fetus's Rh-positive red cells.
- Monoclonal antibodies against respiratory syncytial virus protect high-risk infants.
Active versus passive immunity
| Feature | Active | Passive |
|---|---|---|
| Who makes the antibodies | The person | Another person or an animal |
| Onset of protection | Days to weeks | Immediate |
| Duration | Years or lifelong | Weeks to months |
| Immunological memory | Yes | No |
| Examples | Vaccines, natural infection | Maternal IgG, rabies immune globulin, antitoxin, antivenom |
Clinical notes
- High-risk exposures combine both: the newborn of a hepatitis B surface antigen-positive mother gets vaccine plus immune globulin; severe rabies exposure is also managed with vaccine plus immune globulin.
- Serum sickness after heterologous sera is a type III hypersensitivity: fever, rash, joint pain and lymph node swelling days later.
- Received immune globulin can block injected live vaccines such as MMR and varicella.
Test yourself
Think of the answer, then tap the question to see it.
Which immunoglobulin class crosses the placenta?
IgG, by active transport through the FcRn receptor; it protects the infant during the first months.
What does the newborn of an HBsAg-positive mother receive?
Hepatitis B vaccine (active immunity) and specific immune globulin (passive immunity), ideally within the first hours of life.
Which immunological complication can follow a horse-derived antitoxin?
Serum sickness, a type III hypersensitivity caused by immune complexes against the animal proteins.
Why does passive immunization leave no memory?
Because the person's own lymphocytes are not activated: they only receive ready-made antibodies, which are broken down over time.
Related
- Vaccine types: live, inactivated, subunit, toxoid, mRNA, vector
- Live vaccines: who should not receive them
- Direct and indirect Coombs test
- Serology: IgM vs IgG, seroconversion, avidity
- Neonatal immunity: maternal IgG and breast-milk IgA
- Antibody structure and isotypes (IgG, IgA, IgM, IgE, IgD)
- Type III hypersensitivity (immune complexes)
- ABO and Rh blood groups, hemolytic disease of the newborn
Related conditions
Microorganisms
- Hepatitis B virus
- Rabies virus
- Clostridium tetani
- Corynebacterium diphtheriae
- Varicella-zoster virus
- Measles virus
- Hepatitis A virus
Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.
Sources: Chapter 1: Principles of Vaccination | Pink Book | CDC (Centers for Disease Control and Prevention (CDC), 2021); Chapter 2: General Best Practice Guidance for Immunization | Pink Book | CDC (Centers for Disease Control and Prevention (CDC), 2021).
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Representative model, for educational purposes only.