A Review of the Role of Capsules in the Pathogenesis of Bacterial Meningitis

Meningitis is a disease that affects the meninges, the name given to the three membranes that surround the brain and the spinal cord. The three membranes are called the Dura Mater, the Arachnoid Mater and the Pia Mater. The function of these membranes is to protect the central nervous system.

Meningitis can be caused by both viruses and bacteria. Viral meningitis is more often than harmless and is usually resolved in about a week. Viral meningitis can be caused by viruses such as Entero Viruses and Herpes Viruses.

Bacterial meningitis is less common but far more serious. This paper will be looking at these three in particular, Haemophilus influenzae type b, Neisseria meningitis and Streptococcus pneumoniae bacteria. (Add numbers and who is affected here later)

The reason why these bacteria are a problem is because they have developed ways of getting round the human immune system.

This can be done in multiple ways such as changing their own surface membranes the use of sIgA proteases, an extra cellular enzyme produced by bacteria to cleave human IgA. Bacteria can even invade our own cells to avoid the immune system. They have developed a resistance to Nitric Oxide, the cells natural antibacterial.

But among the most troubling, however, is the way is they avoid phagocytosis and the compliment system. Both fall under the umbrella of the inflammatory response and both are key features of the non-specific defence in the immune system.

Phagocytosis and compliment are two of only three ways of non-specific immune response methods in the blood and even then, in the case of some of these meningitis strains the other method is neutralized and turned into an asset for their own survival inside the blood stream.

This paper will lo...

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...3 convertase) will cleave more C3 proteins and start a MAC from there. The lectin pathway starts when MBL, a serum protein bind itself to the surface of a pathogen.

A few capsules can prevent the formation of C3Bb, which as mentioned in the previous paragraph is essential to start the alternative pathway as a C3 convertase. This is done through making serum protein B fail to bind to C3b. Less C3 convertase means that there is less 3b to go around to make C5 convertase. Combined, this drastically reduces the chances of a MAC forming. Capsules do not make bacteria serum resistant, but just a lot more unlikely to be killed by the inflammatory response.

This is due to proteins still being able to go through the capsule and form on the bacterial membrane surface. The polysaccharide polymer network is largely loose and unstructured which means it is not impenetrable.