Hormonal regulation of the immune response
Immune responses do not exist in isolation: they develop against the background of hormonal regulation, which operates on the classical feedback principle. General metabolism is critically important for defense. For example, pronounced metabolic disorders can lead to underdevelopment of the thymus (thymic gland), which automatically causes weakened immunity and the development of immunodeficiency.
According to their vector of influence on the immune system, hormones are divided into two groups:
- Immunostimulants (activate defense reactions): insulin, thyroxine (thyroid hormone), and somatotropin (growth hormone of the anterior pituitary). A deficiency of growth hormone negatively affects the immune status.
- Immunosuppressants (suppress defense): glucocorticoids and all major sex hormones (androgens, estrogens, progesterone).
A striking clinical example of the link between the endocrine system and reactivity is diabetes mellitus. Such patients have a dramatically increased susceptibility to pyogenic infections. Immunodeficiency in diabetes is caused by three factors: a general severe metabolic disorder, the loss of the physiological stimulating effect of insulin on immunity, and direct inhibition of phagocytosis processes.
Genetic polymorphism and mechanisms of resistance
Individual resistance of the organism has strict genetic determination. Genes control not only protection against the initial onset of infection, but also resistance to its development. Moreover, genetics determines the organism's ability to keep the pathogen in a latent (dormant) state, and also forms the phenomenon of specific resistance to specific phases of the microorganism's life cycle.
There are two main mechanisms for implementing genetic resistance:
- Via the immune system. First and foremost, this is due to the functioning of major histocompatibility complex (MHC) antigens. A huge role is played by mutations in genes that are directly responsible for the quality of phagocytosis, the proper differentiation of T- and B-lymphocytes, and the synthesis of signaling molecules—cytokines (specifically, interferons).
- Outside the immune system (metabolic defense). This mechanism is directed against highly specialized microbes, which require strictly defined tissue substrates for nutrition and reproduction. If a genetic mutation alters the structure of such a substrate, the pathogen loses the ability to utilize it and dies without the direct participation of immune cells.
Host-pathogen interaction
The development of an infection is always a dynamic balance of forces. Factors that enhance non-specific resistance and immunity block the development of the pathological process. Conversely, any triggers that reduce host defense promote the unhindered spread and generalization of infection.
The interaction between reactivity and the microbe has a crucial evolutionary aspect, as the macroorganism acts as an environment for strain selection:
- In an immunodeficient organism, defense is minimal, so the pathogen does not need to spend resources on adaptation and "hiding." In such comfortable conditions for the microbe, selection occurs for highly virulent strains capable of maximally aggressive reproduction.
- In an immune (resistant) organism, the microbe has to survive under the constant pressure of defense systems. Aggressive individuals are rapidly destroyed, so predominantly weakly virulent strains survive and are selected, as they are forced to adapt to the powerful host response.
Briefly: answers to topical questions
Which cytokine groups are involved in the implementation of genetic resistance?
Genetic resistance via the immune system involves cytokines, particularly interferons, as well as the genes responsible for their synthesis.
Which classes of major histocompatibility complex (MHC) antigens participate in the immune response?
The immune response involves class I major histocompatibility complex antigens, represented by HLA-A, HLA-B, and HLA-C types on nucleated cells, and class II MHC antigens, including HLA-DR, HLA-DP, and HLA-DQ types on professional antigen-presenting cells.
Stimulatory hormones are easily remembered by the acronym SIT: Somatotropin, Insulin, Thyroxine.
Class and exam questions
Why are pyogenic infections so dangerous in diabetes mellitus?
Diabetes causes complex immunodeficiency: general metabolism is impaired, the immunostimulating effect of insulin is lost, and phagocytosis is directly suppressed. This deprives the body of adequate protection against pyogenic bacteria.
How is metabolic genetic resistance implemented?
It targets highly specialized microbes. Due to mutations in host tissues, the structure of nutritional substrates changes, and the microbe loses the ability to utilize them, dying of starvation.
Which bacterial strains undergo selection in a resistant organism?
In an organism with strong immunity, weakly virulent strains are selected. They have to adapt to powerful host defenses, while overly aggressive, highly virulent forms are quickly recognized and destroyed.
What else to study on this topic
- Mechanisms of phagocytosis suppression in insulin deficiency
- The role of major histocompatibility complex (MHC) antigens in the infectious process
- The effect of glucocorticoids on lymphocyte differentiation
- Genetically determined phase resistance to pathogen life cycles
Study the full topic in the «Microbiology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Host Reactivity Factors and the Infectious Process" and 4,383 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 141 video lectures on the subject
Other topics in the section "Study of Infection"
Free video lessons: microbiologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.