Evolution of vaccination: from observation to science
The development of methods for protection against infections went through two key stages:
- Empirical stage (late 18th century). Edward Jenner, based on observations, used cowpox pustule material to vaccinate humans against smallpox. The biological mechanism of the phenomenon had not yet been studied at that time.
- Scientific stage (late 19th century). Louis Pasteur scientifically substantiated the principle of vaccination. He developed the method of attenuation—weakening the pathogen using temperature, an unfavorable environment, or passages through non-susceptible animals. With this approach, the microbe loses pathogenicity but retains the ability to induce a specific immune response. Pasteur created vaccines against anthrax, chicken cholera, and rabies (the first live attenuated vaccine).
To provide mass assistance to the population, including victims of animal bites, special vaccination stations began to open. The first such "Pasteur station" in Russia appeared in 1886 in Odessa through the efforts of Ilya Mechnikov and Nikolai Gamaleya. And in 1888, the Pasteur Institute was opened in Paris through public donations.
Founders of immunology and their debate
The understanding of exactly how the body fights infections was born in discussions among prominent scientists.
Ilya Mechnikov developed the phagocytic theory. He proved that phagocytosis is a universal biological mechanism providing protection against foreign agents (including bacteria) at the cellular level. Mechnikov also laid the foundations of gerontology and the study of normal microflora (dysbiosis).
His opponent was Paul Ehrlich, author of the humoral theory. Ehrlich believed that the main role in defense belongs to specific substances in body fluids—antibodies.
Further research proved both scientists right. Modern science recognizes the unity of cellular and humoral defense factors. In 1908, Ilya Mechnikov and Paul Ehrlich jointly received the Nobel Prize.
Development of immunology in the 20th century
In the first half of the 20th century, scientists began studying immune responses not directly related to defense against infections:
- Allergy (hypersensitivity): Delayed-type (R. Koch, 1900) and immediate-type reactions were described. In 1906, C. Pirquet united them under the term "allergy".
- Immunological memory: The phenomenon of accelerated antibody production upon re-exposure to an antigen was described (M. Raisky, 1915).
- Tolerance: In the 1950s, P. Medawar and M. Hašek discovered the phenomenon of immunological tolerance to antigens.
By the mid-20th century, the study of mechanisms at the molecular and cellular levels began. The structure of immunoglobulins was deciphered, interferons and interleukins were discovered, and lymphocytes were divided into T- and B-systems. During this time, immunology finally formed as an independent medical discipline with its own tasks and classification.
Briefly: answers to topical questions
What classes of immunoglobulins are synthesized in the human body?
Five main classes (isotypes) of immunoglobulins are synthesized in the human body. These include:
- IgG — includes subclasses IgG1-4, serves as a marker of secondary infection or past infection.
- IgM — acts as a marker of acute infection.
- IgA — detected in secondary infection, chronic infection, and carriage.
- IgE — a marker of allergopathology, normally practically undetectable.
- IgD — one of the five antibody isotypes produced by plasma cells.
Which blood and tissue cells are considered professional phagocytes?
Professional phagocytes include macrophages and dendritic cells. Granulocytes also exhibit pronounced phagocytic activity:
- Macrophages — powerful cytokine producers that carry out phagocytosis.
- Dendritic cells — capture antigen via pinocytosis and less frequently phagocytosis.
- Neutrophils — microphages that phagocytize bacteria and small tissue debris.
- Basophils — like all granulocytes, are also capable of phagocytosis.
What are the main subpopulations of T-lymphocytes?
T-lymphocytes are subdivided into several subpopulations:
- T-helper cells (CD4+) — include naive cells ($T_H0$), effector subpopulations $T_H1$, $T_H2$, $T_H17$, as well as follicular T-helper cells (Tfh).
- Regulatory T-lymphocytes ($T_{Reg}$).
- Cytotoxic T-lymphocytes (CD8+) — provide the cellular arm of the adaptive response.
- $\gamma\delta$-T-lymphocytes — localize in the dermis.
Which proteins belong to humoral factors of non-specific resistance?
Humoral factors of non-specific resistance mentioned in the sources include:
- Mannose-binding lectin — a soluble innate defense receptor.
- C-reactive protein — a soluble innate defense factor.
- Complement system proteins.
- Interferons.
- Lysozyme.
- $\beta$-lysins.
What types of allergic reactions are distinguished according to the Gell and Coombs classification?
According to the Gell and Coombs classification, four main types of allergic reactions are distinguished. These include:
- Type I (Anaphylactic) — an immediate-type reaction where IgE is the main mediator.
- Type II (Cytotoxic) — mediated by IgG and IgM antibodies in reactions of target cell cytolysis.
- Type III (Immune complex) — associated with the formation of antigen-antibody complexes and subsequent tissue damage.
- Type IV — delayed-type hypersensitivity (DTH), mediated by cellular immunity.
To remember the two main theories of immunity, associate: Mechnikov (Sword/Mech) — cells fight like warriors (phagocytosis, cellular immunity). Ehrlich (Elixir) — defense is in fluids (antibodies, humoral immunity).
Class and exam questions
What is attenuation in the context of vaccination?
Attenuation is the artificial weakening of an infection's pathogen. As a result, the microbe ceases to be pathogenic but retains the ability to induce an immune response (immunogenicity).
How did Jenner's empirical vaccination differ from Pasteur's approach?
Jenner used a method based on a lucky observation without understanding the biological causes. Pasteur, on the other hand, provided a scientific basis for vaccination, proving that protection requires precisely the weakened pathogen of a specific disease.
Who won the scientific dispute between Metchnikoff and Ehrlich?
Both won. Science proved that immunity is provided by the joint action of both phagocytic cells (Mechnikov's theory) and antibodies in body fluids (Ehrlich's theory).
What else to study on this topic
- Contribution of the Pasteur school (A. Laveran, J. Bordet, É. Roux, and A. Calmette)
- Types and mechanisms of allergic reactions (Immediate and Delayed Type Hypersensitivity)
- A.M. Bezredka's desensitization method
- Structure and functions of immunoglobulins
- Division of lymphocytes into T- and B-systems and their interaction
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