Port of entry and primary colonization
Transmission occurs via airborne droplets during close contact. The pathogen enters the nasopharyngeal epithelium with saliva and mucus.
The process begins by overcoming non-specific defenses (mucociliary clearance). Using pili, bacteria attach to mucosal cell CD46 receptors. Outer membrane proteins and CD66 receptors are used for additional adhesion.
Following colonization, dendritic cells and macrophages capture pathogen antigens and transport them to regional lymph nodes to initiate an immune response. The incubation period lasts from 1 to 10 days.
If the immune response is formed adequately and rapidly, the process remains restricted to the mucosa. Asymptomatic bacterial carriage develops and may last for months.
Development of local inflammation
When local defense is insufficient, the meningococcus penetrates deeper into the submucosa, where it undergoes phagocytosis. Upon bacterial destruction, their main pathogenic factor—lipooligosaccharide (LOS)—is released, acting as a potent endotoxin.
LOS initiates the release of inflammatory mediators:
- Proteins: interleukins, interferons, TNF.
- Lipids: prostaglandins, leukotrienes.
- Other agents: reactive oxygen species and lysosomal enzymes.
These mediators damage the local endothelium, increasing vascular permeability. Local inflammation develops—acute meningococcal nasopharyngitis. Small doses of toxins and the bacteria themselves may enter the bloodstream, causing short-term intoxication.
Generalization of infection (meningococcemia)
Once barriers are breached, bacteria massively enter the bloodstream and actively multiply (aided by their ability to utilize iron from blood proteins).
Bacteremia results in massive endotoxemia—a sharp increase in the concentration of LOS and pro-inflammatory cytokines in the blood.
Pathogenetic mechanisms of meningococcemia:
- Severe systemic damage to the vascular endothelium throughout the body.
- Systemic vasodilation and increased vascular permeability.
- Plasma leakage into tissues (extravasation).
- Development of generalized vasculitis and microthrombosis.
- Microcirculatory disturbances leading to tissue hypoxia, organ necrosis, and DIC syndrome.
Penetration into the CNS and cerebral edema
Meningococci circulating in the blood can settle on the endothelium of the pia mater and choroid plexuses. They cross the blood-brain barrier (BBB) via endocytosis.
Purulent inflammation develops in the CNS:
- Meningitis (pia mater).
- Ependymitis or ventriculitis (ventricular ependyma).
- Encephalitis (brain parenchyma).
Inflammation is accompanied by plasma transudation and leukocyte migration. Hyperproduction of cerebrospinal fluid and impaired outflow lead to a sharp rise in intracranial pressure. Toxins damage cerebral vessels, causing hypoxia and failure of cerebral blood flow autoregulation. The most formidable complication of this cascade is cerebral edema and swelling.
Briefly: answers to topical questions
What aggression enzymes does the meningococcus use to cleave immunoglobulins on the mucosa?
To cleave immunoglobulins on the nasopharyngeal mucosa, sources cite the enzyme IgA1 protease (IgA protease). It cleaves secretory immunoglobulin A in the hinge region and inactivates normal secretory antibodies on the nasopharyngeal mucosa, protecting bacteria from antibody action.
What is the exact mechanism of DIC syndrome activation by meningococcal endotoxin?
DIC syndrome in generalized meningococcal infection is associated with the action of the meningococcal endotoxin—LOS. In meningococcemia, endotoxemia and the concentration of pro-inflammatory mediators sharply increase. The endotoxin causes the activation of leukocytes, macrophages, endothelial cells, platelets, and blood clotting factors. Key links: endothelial damage; systemic vasodilation and increased vascular permeability; plasma and cellular extravasation; development of vasculitis and microcirculatory thrombosis; alteration of blood rheological properties; impaired tissue perfusion and hypoxia. The result is the development of DIC syndrome, necrosis formation, and organ dysfunction.
Class and exam questions
What is the specific feature of meningococcal endotoxin?
Their cell wall contains lipooligosaccharide (LOS) with few polysaccharide O-chains. Consequently, lipid A is poorly shielded, making LOS toxicity significantly higher than that of LPS from other Gram-negative bacteria.
Why is meningococcus able to survive in the blood?
It possesses specialized siderophores on its outer membrane that scavenge iron from transferrin, haptoglobin, and hemoglobin, which is critically important for its viability and dissemination.
How does meningococcus protect itself from phagocytosis?
Highly virulent strains form a polysaccharide capsule that prevents complement-mediated bacteriolysis and phagocytosis by macrophages and neutrophils.
What else to study on this topic
- Structural components and serogroups of Neisseria meningitidis
- Epidemiology and seasonality of meningococcal infection
- Risk groups and the role of complement deficiency (C6-C9)
- The role of IgA1 protease in overcoming local immunity
- Mechanisms of asymptomatic carriage formation
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