Corynebacterium diphtheriae is the causative agent of diphtheria, named for the grayish-white pseudomembrane of the mucous membrane of the patient's throat. The source of infection is the patient and the carrier, with droplets and toys as the medium of infection, causing acute respiratory tract infection. The bacterium does not invade the blood, but localizes in the mucous membrane and produces diphtheria toxin, which causes local inflammation and invades the blood to form toxemia, resulting in systemic toxic symptoms. Diphtheria toxin has a strong cytotoxic effect, can make the local mucosal epithelial cells produce inflammation, exudation and necrosis, exudate cellulose and local bacteria, inflammatory cells, necrosis of the mucosa tightly combined together to form a pseudomembrane, it is not easy to wipe off. If the pseudomembrane extends and falls off in the trachea, it can cause the patient to die of asphyxiation in the early stage of the disease.

The diphtheria toxin is an zymogen, degraded by enzyme proteins, divided into A and B polypeptide fragments, B peptide chain is not enzymatically active, there is a receptor-binding region and a translocation region, and susceptible to the cell surface receptor binding, showing its selective affinity; A peptide chain is enzymatically active, but can not be invaded into the cell alone; usually the A peptide chain by the B peptide chain to carry, attached to the cell membrane receptor and transported to the cytoplasm.A peptide chain makes the intracellular elongation factors. A peptide chain inactivates intracellular elongation factor II (EF-2) and impairs protein synthesis in susceptible cells. Common susceptible cells are myocardium, peripheral nerves, liver, kidney, adrenal gland and other tissues, which can cause corresponding clinical symptoms.

Immune mechanism: humans have a certain tolerance to diphtheria toxin, a sufficient amount of diphtheria toxin can stimulate the body to produce an adequate immune response, so the disease can be obtained after the main humoral immunity of solid immunity.