The infectious process triggers complex systemic changes, in which adaptive and pathological reactions of the nervous and immune systems play a key role. Understanding these mechanisms helps evaluate disease dynamics from the incubation period to recovery.
CNS ReactionInitial activation during stress is followed by depression as intoxication increases.
ImmunopathologyIncludes allergy, autoimmunity, immunodeficiencies, and pathological tolerance.
Antigenic MimicryStructural similarities between microbial and host antigens lead to autoimmune reactions.
Stages of InfectionInfection progresses through 4 stages: incubation, prodromal, peak, and resolution.
Nervous System: From Adaptation to Exhaustion
Upon pathogen invasion, the nervous system responds with a stress response aimed at mobilizing resources.
Adaptation: The body attempts to localize the infection and normalize physiological functions.
Intoxication: With massive toxin exposure, the activation phase gives way to profound central nervous system depression.
Neurotrophic Disorders: Specific lesions (e.g., in botulism) disrupt organ function.
Central mechanisms also affect the respiratory center, suppressing its activity, which, combined with peripheral lung damage, worsens the patient's condition.
Immune System: Failure of Immune Surveillance
Normally, the immune system aims to eliminate the pathogen, but infections often provoke pathological states:
Allergy: Most commonly type III (immune complex hypersensitivity), occurring in the presence of antigen excess.
Immune Autoaggression: Develops due to the modification of self-antigens, antigenic mimicry, or the integration of viral DNA into the host genome.
Immunodeficiencies: Usually transient, but become persistent in HIV infection, blocking the immune response and promoting pathological tolerance.
Systemic Consequences
The infectious process is not limited to the primary site of injury. Toxins and metabolic disturbances cause:
What are the mechanisms of pathological immunological tolerance during infections?
Mechanisms of pathological immunological tolerance include hyporegenerative processes and impaired foreign antigen recognition.
Hyporegenerative mechanism — suppression of hematopoietic stem cell and multipotent cell proliferation.
Immunodeficiency states — generalized impairment of immune function.
Masking of antigenic determinants — shielding of foreign cells by antibodies, preventing recognition by cytotoxic T cells.
Deficient T-cell co-stimulation — absence of the secondary activation signal leads to anergy.
Increased T-suppressor activity — excessive suppression of the immune response.
Antigenic overload — excess antigen exhausts resources or blocks receptors.
Which pathogens can integrate viral DNA into the host cell genome?
Pathogens capable of integrating viral DNA into the host cell genome include:
DNA viruses — circular double-stranded viral DNA attaches to host DNA at homology regions and integrates into a specific chromosomal locus, mediated by restriction enzymes, endonucleases, and ligases.
Retroviruses (e.g., HIV) — reverse transcriptase synthesizes DNA from a viral RNA template, which then integrates into the host chromosome to form a provirus.
Which bacterial toxins, other than botulinum toxin, cause specific neurotrophic disorders?
In addition to botulinum toxin, the nervous system can be damaged by the exotoxin of the tetanus pathogen (Clostridium tetani), which triggers generalized tonic and tetanic seizures accompanied by marked muscle hypertonia.
Why do autoimmune reactions occur during an infection?
They occur due to antigenic mimicry (similarities between microbial and host antigens), modification of self-proteins by toxins, or the integration of viral DNA into host cell genomes.
Which types of allergic reactions are most characteristic of infections?
Type III hypersensitivity reactions (Gell and Coombs classification) associated with immune complex formation are most commonly observed.
Are infection-related immunodeficiencies permanent?
In most cases, they are transient. An exception is seen in conditions with direct destruction of immune cells, such as HIV/AIDS.
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