Which cytokine groups participate in the realization of genetic resistance?

Cytokines, particularly interferons, as well as the genes responsible for their synthesis, participate in genetic resistance mediated through the immune system.

Which classes of major histocompatibility complex (MHC) antigens participate in the immune response?

Class I MHC 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, participate in the immune response.

Why are pyogenic infections so dangerous in diabetes mellitus?

Diabetes causes a complex immunodeficiency: general metabolism is disrupted, the immunostimulatory effect of insulin is lost, and phagocytosis is directly suppressed. This deprives the body of adequate protection against pyogenic bacteria.

How is metabolic genetic defense 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?

Low-virulence strains are selected in an organism with strong immunity. They must adapt to the powerful host defenses, whereas overly aggressive, highly virulent forms are rapidly recognized and destroyed.

Host Reactivity Factors in Infection: USMLE Review

Host Reactivity Factors and the Infectious Process

For medical students2 min readUpdated 2026-10-10

The clinical presentation of any infection is the result of a confrontation between the pathogen's properties and the host's reactivity. The body's ability to resist a pathogen is multifaceted: it is strictly genetically determined and operates under the continuous control of the neuroendocrine system.

ImmunosuppressantsGlucocorticoids and sex hormones predictably suppress the body's immune responses.

DiabetesInsulin deficiency impairs phagocytosis, paving the way for pyogenic bacterial infections.

Metabolic DefenseMutations in tissues deprive highly specialized microbes of the necessary nutritional substrate.

Microbial SelectionWeak immunity selects for highly virulent pathogens, whereas strong immunity selects for low-virulence strains.

Hormonal Regulation of the Immune Response

Immune responses do not exist in isolation: they develop against the background of hormonal regulation operating via a classical feedback loop. General metabolism is critically important for host defense. For example, marked metabolic disturbances can lead to thymus hypoplasia, which automatically causes weakened immunity and the development of immunodeficiency.

Depending on their vector of influence on the immune system, hormones are divided into two groups:

Immunostimulants (activate defensive reactions): insulin, thyroxine (thyroid hormone), and somatotropin (growth hormone from the anterior pituitary). Growth hormone deficiency negatively affects immune status.
Immunosuppressants (suppress defenses): 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. Patients with this condition have a sharply increased susceptibility to pyogenic infections. Immunodeficiency in diabetes is caused by three factors: a severe general metabolic disorder, the loss of the physiological stimulating effect of insulin on immunity, and direct suppression of phagocytosis.

Genetic Polymorphism and Resistance Mechanisms

Individual resistance of the organism is strictly genetically determined. Genes control not only protection against the initial onset of infection but also resistance to its progression. Furthermore, genetics determines the organism's ability to keep a pathogen in a latent state and shapes the phenomenon of specific resistance to particular phases of the microbial life cycle.

There are two main mechanisms for realizing genetic resistance:

Via the immune system. This is primarily driven by the major histocompatibility complex (MHC) antigens. A huge role is played by mutations in genes directly responsible for the quality of phagocytosis, proper differentiation of T and B lymphocytes, and the synthesis of signaling molecules—cytokines (particularly interferons).
Outside the immune system (metabolic defense). This mechanism targets highly specialized microbes that require strictly specific 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 increase nonspecific resistance and immunity block the development of the pathological process. Conversely, any triggers that diminish host defenses promote the unimpeded spread and generalization of the infection.

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 expend resources on adaptation or evasion. Under such hospitable conditions for the microbe, highly virulent strains capable of maximum aggressive replication are selected.
In an immune (resistant) organism, the microbe must survive under the continuous pressure of defense systems. Aggressive individuals are rapidly eliminated, and therefore predominantly low-virulence strains that are forced to adapt to the powerful host response survive and are selected.

Mnemonic

Stimulatory hormones can be easily remembered by the acronym SIT: Somatotropin, Insulin, Thyroxine.

Frequently asked questions

Which cytokine groups participate in the realization of genetic resistance?: Cytokines, particularly interferons, as well as the genes responsible for their synthesis, participate in genetic resistance mediated through the immune system.
Which classes of major histocompatibility complex (MHC) antigens participate in the immune response?: Class I MHC 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, participate in the immune response.
Why are pyogenic infections so dangerous in diabetes mellitus?: Diabetes causes a complex immunodeficiency: general metabolism is disrupted, the immunostimulatory effect of insulin is lost, and phagocytosis is directly suppressed. This deprives the body of adequate protection against pyogenic bacteria.
How is metabolic genetic defense 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?: Low-virulence strains are selected in an organism with strong immunity. They must adapt to the powerful host defenses, whereas overly aggressive, highly virulent forms are rapidly recognized and destroyed.

Go deeper

Mechanisms of phagocytosis suppression in insulin deficiency
The role of major histocompatibility complex (MHC) antigens in the infectious process
Effect of glucocorticoids on lymphocyte differentiation
Genetically determined phase resistance to pathogen life cycles