Polysaccharides are strings of sugars. Some bacteria, such as Streptococcus pneumoniae and Neisseria meningitidis, have large amounts of polysaccharide on their surface, which encapsulate the bacteria. The polysaccharide capsules protect the bacteria from the host’s immune system and can make the bacteria more virulent.
Polysaccharide vaccines are poorly immunogenic. They produce low affinity antibodies (which do not bind well to the antigen) and, because they do not elicit T-cell responses, immune memory does not develop.
The new generation conjugate vaccines contain carrier proteins that are chemically attached to the polysaccharide antigens. Attaching relatively non-immunogenic polysaccharides to the highly immunogenic carrier proteins means that by activating a T-cell response, conjugate vaccines induce both high-affinity antibodies against the polysaccharide, and immune memory.
So in conclusion:
The new generation conjugate vaccines contain carrier proteins that are chemically attached to the polysaccharide antigens. Attaching relatively non-immunogenic polysaccharides to the highly immunogenic carrier proteins means that by activating a T-cell response, conjugate vaccines induce both high-affinity antibodies against the polysaccharide, and immune memory.
So in conclusion:
Polysaccharide vaccine - T cell independent B cell response
Conjugate vaccine - Carrier proteins - T cell dependent B cell response
Mnemonic:
CT (Like a CT scan?)
ConjugaTe has a T cell response
That's all!
-IkaN
And this is the reason why polysaccharide vaccine is not given to children less than 2yrs of age
ReplyDeleteConjugate vaccine is prefferd for them