Immune sera and immunoglobulins

Functional groups and formulation types

Specific antibodies serve as the primary immunoreagents that determine a person's immune status. Depending on the nature of their target, they are divided into several major groups: antibacterial, antiviral, antitoxic, as well as antitumor, transplantation, and cytotoxic antibodies.

In addition to classical sera, the modern arsenal includes numerous formats:

• Whole-molecule and domain immunoglobulins.
• Monoclonal antibodies.
• Immunotoxins and immunoadhesins.
• Abzymes (antibodies capable of acting as enzymes).

Classification by origin

The duration of protection and the safety of therapy directly depend on the source of the immune proteins. Two classes of sera are distinguished:

1. Heterologous (heterogeneous). These are produced in the bodies of animals. Due to the presence of foreign proteins, they are characterized by high reactogenicity. The protective effect lasts for a relatively short time after administration — from two to three weeks.
2. Homologous. Human blood serves as the source (taken from convalescents, immunized donors, or obtained from placental and aborted blood). Because these proteins are compatible with the patient's body, side effects occur significantly less often, 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 hundred years ago. Today, the basis for obtaining heterologous agents is hyperimmunization — the intensive and repeated administration of an antigen to producer animals (horses, donkeys, rabbits). When the concentration of protective proteins reaches its maximum, bleeding is performed, followed by serum isolation.

Native preparations contain a huge amount of ballast macromolecules (such as albumins) that do not participate in the immune response. Physico-chemical processing is used to isolate the target immunoglobulins:

• Acetone or alcohol precipitation 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. Titer is defined as the minimum amount of antibody capable of causing a visible reaction with the antigen, or the maximum 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 amount of antitoxin that neutralizes a specified number of lethal doses (Dlm) for a laboratory animal.
• Agglutinating and precipitating sera are evaluated by their 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 use and safety

Therapeutic use requires the administration of large doses (intravenously or intramuscularly) as early as possible in the course of the disease. Prophylactic use is indicated in emergency situations—after contact with an infectious patient. 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 the Besredka 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. Ready-made antibodies provide rapid but short-term protection, which is succeeded in 2–3 weeks by persistent active immunity from the vaccine.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Structure and functions of various immunoglobulin classes.
• Nature and methods of obtaining monoclonal antibodies.
• Catalytic antibodies (abzymes): mechanism of enzymatic activity.
• Immunotoxins and immunoadhesins: promising areas of therapy.
• Detailed analysis of performing allergy tests before serotherapy.

Other topics in the «Immunoprophylaxis Agents» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.