Direct Damage Mechanisms

Adhesion Damage

Various accessory proteins are required to assist the P1 protein, allowing it to adhere to the host. This includes:
P30 adhesion factor related protein (A,B and C)
HMW 1-5 polypeptides
P40, P90, P65
Together, these form an adhesion protein complex, enabling P1 proteins on the tip of the organelle to adhere to the host cell.

The absence of a rigid cell wall allows M. pneumoniae to fuse with the host cell and avoid detection by the host’s immune system
M. pneumoniae is highly fusogenic. The lipid bilayer of the cell membrane fuses with the host cell.
Membrane fusion can cause changes in the receptors of the host cell membrane, which disrupts cell signalling.

M. pneumoniae cannot synthesize amino acids, fatty acids and vitamins due to its small genome.
After adhering to the respiratory epithelia, it is able to insert its microtubules into the host. This allows M. pneumoniae to consume the host’s oxygen, glucose, absorb cholesterol, ingest amino acids and consume its nutrients. Consequently, this causes damage to the host cell.

Once M. pneumoniae adheres to the surface of bronchial cells, it triggers the rearranging of its cytoskeleton. This allows it to enter the bronchial mucous membrane, releasing hydrogen peroxide.
Hydrogen peroxide and superoxide are products of Mycoplasma metabolism and cause oxidative damage to the host tissues. Hydrogen peroxide is associated with decreased movement of microvilli, necrosis and activation of lymphocytes, monocytes and plasma cells.
The absence of superoxide dismutase and catalase in M. pneumoniae causes the host cell to release hydrogen peroxide along with toxic oxygen molecules. Subsequently, oxidative stress occurs eventually leading to the death cell death.
M. pneumoniae also produces an exotoxin, known as community acquired respiratory distress syndrome (CARDS) toxin. This is an ADP-ribosylating and vacuolating toxin, inducing pulmonary eosinophilic and lymphocytic inflammation.

Direct Damage Mechanisms: Other Projects