Functional Groups and Formats of Preparations
Specific antibodies serve as core immunoreagents that define a person's immune status. Depending on the nature of the target, they are divided into several major groups: antibacterial, antiviral, antitoxic, as well as antitumor, transplantation-related, and cytotoxic.
In addition to classical sera, the modern arsenal includes many formats:
- Whole-molecule and domain immunoglobulins.
- Monoclonal antibodies.
- Immunotoxins and immunoadhesins.
- Abzymes (antibodies capable of functioning as enzymes).
Classification by Origin
The duration of protection and safety of therapy directly depend on the source of immune proteins. There are two classes of sera:
- Heterologous (heterogenic). These are produced in animal organisms. Due to the presence of foreign proteins, they have high reactogenicity. The protective effect after administration is relatively short-lived, lasting about two to three weeks.
- Homologous. Human blood serves as the source (obtained from convalescents, immunized donors, or derived from placental and aborted blood). Because the proteins are homologous to the patient's body, side effects are significantly fewer, and passive immunity lasts longer — about 4–5 weeks.
Production and Purification Technology
Historically, the first sera against anthrax and diphtheria were created by E. von Behring over a century ago. Today, the basis for producing heterologous agents is hyperimmunization — intensive and repeated administration of the antigen to producer animals (horses, donkeys, rabbits). When the concentration of protective proteins reaches its maximum, bleeding is performed, followed by serum separation.
Native preparations contain a large number of ballast macromolecules (such as albumins) that do not participate in the immune response. Physicochemical processing is used to isolate target immunoglobulins:
- Precipitation with acetone or alcohol at low temperatures.
- Ultrafiltration and affinity chromatography.
- Enzymatic treatment.
Domain antibodies, which represent isolated antigen-binding regions of the molecule (Fab fragments), possess the highest specificity.
Standardization and Potency Evaluation
The efficacy of preparations is expressed in titers or specialized units. The titer is defined as the minimum amount of antibody capable of causing a visible reaction with the antigen, or as the maximal dilution at which this reaction is recorded.
- Antitoxic sera are measured in international units (IU) or antitoxic units (AE). The standard is taken as the volume of antitoxin that neutralizes a specified number of lethal doses (Dlm) for a laboratory animal.
- Agglutinating and precipitating sera are evaluated by the maximum working dilution.
- Virus-neutralizing sera are standardized by the dilution capable of suppressing the virus in bioassays (in cell cultures, animals, or chicken embryos).
Clinical Application and Safety
Therapeutic application requires administration of large doses (intravenously or intramuscularly) as early as possible in the course of the disease. Prophylactic use is indicated in emergency situations, such as contact with an infected individual. In this case, dosages are significantly lower.
To prevent serum sickness and anaphylactic shock, a preliminary allergy skin test is mandatory. The preparation itself is administered using Bezdredka's method — in fractional doses for gradual desensitization.
In special cases (tetanus in wounded patients, risk of rabies), passive-active immunization is used. Both the vaccine and the serum are administered to the patient simultaneously. The preformed antibodies provide rapid but short-term protection, which is succeeded after 2–3 weeks by lasting active immunity induced by the vaccine.