Serotherapy is a medical treatment that uses serum—the liquid component of blood—collected from a human or animal with immunity to a specific disease. The core of this treatment involves transferring proteins called antibodies from the immune donor to the recipient. This transfer helps the recipient fight off an infection by providing a temporary, immediate defense known as passive immunity.
The Mechanism of Serotherapy
The effectiveness of serotherapy lies in delivering ready-made antibodies to an individual. This process provides passive immunity, which is distinct from active immunity that occurs when your body makes its own antibodies after an infection or vaccination. Active immunity provides a long-lasting defense built by your own system.
In contrast, passive immunity from serotherapy offers immediate but short-term protection. The donated antibodies are eventually broken down by the body, and protection fades over weeks or months.
Applications in Disease Treatment
Historically, serotherapy was a groundbreaking treatment for infectious diseases before the widespread availability of antibiotics. In the late 19th and early 20th centuries, it was used to treat diseases like diphtheria and tetanus, improving survival rates. While many of its original uses have been replaced by vaccines and antimicrobial drugs, serotherapy remains an important tool in modern medicine.
One of its most common modern uses is in antitoxins, which are preparations of antibodies that neutralize specific toxins. These are administered to treat venomous bites from snakes and spiders, and to combat bacterial toxins that cause botulism and tetanus. In these cases, the body does not have time to mount its own effective immune response, so receiving a concentrated dose of targeted antibodies can be necessary.
Another application is the use of hyperimmune globulins, solutions of antibodies from donors with high immunity to a specific disease. These are given as post-exposure prophylaxis after a person has been exposed to a pathogen but before they develop symptoms. Examples include rabies immunoglobulin after an animal bite or tetanus immunoglobulin for a deep wound. This provides an immediate defense while the individual’s own immune system begins to build a long-term response.
During recent viral outbreaks, convalescent plasma has been explored as a form of serotherapy. This involves collecting blood plasma from individuals who have recovered from an infection, such as Ebola or COVID-19, and transfusing it into sick patients. The theory is that the antibodies from the recovered patient can help the recipient clear the active infection.
Production of Therapeutic Sera
The creation of therapeutic serum begins with obtaining antibodies from either human or animal sources. For convalescent plasma and hyperimmune globulins, the source is human volunteers with high concentrations of the desired antibodies. For many antitoxins needed in large quantities, like antivenoms, animals such as horses are used. These animals are immunized with a safe form of a toxin or pathogen to stimulate a strong immune response.
Once high levels of antibodies are present, blood is collected from the donor and processed to separate the serum or plasma. This raw material undergoes extensive purification to isolate and concentrate the specific antibodies, removing other components that could cause adverse reactions. The final product is sterilized and standardized to ensure each dose has a consistent and effective concentration of antibodies.
Associated Risks and Complications
Serotherapy is not without risks. A primary concern, especially with sera from animal sources, is a condition called serum sickness. This is an immune system reaction to the foreign proteins in the donated serum, which can cause symptoms like fever, rash, and joint pain to appear days or weeks after treatment. Modern purification techniques have reduced the incidence of this complication, but the risk remains.
More immediate and severe reactions can also occur, including anaphylaxis, a rapid and potentially life-threatening allergic reaction. Patients are carefully monitored after receiving serotherapy for this reason. Because the treatment involves transferring a biological product, there is also a risk of transmitting blood-borne pathogens. Rigorous screening of donors and advanced purification methods have made this risk extremely low.