polysaccharide and plysaccharide conjugate

what is a vaccination

a vaccination is a form of active immunity in which a pathogen is introduced to a host to stimulate the immune system and form immunogenic memory so when the host come in contact with the pathogen again it has a fast and strong immune response

what do important bacterial pathogens possess

polysaccharide capsules thath function as major virulence factors by preventing phagocytosis

what makes the capsules important

because they are exposed on the bacterial surface they are a key target for vaccine development

what kind of capsule has been developed

vaccines that use purified capsular polysaccharides to stimulate protective antibody responses

differences

pure polysaccharide vaccines and polysaccharide conjugate vaccines stimulate different types of immune responses, which leads to major differences in their effectiveness, particularly in young children.

what are polysaccharide vaccines

composed of purified capsular polysaccharides from bacterial pathogens

what is an example of a polysaccharide vaccine

pneumococcal polysaccharide vaccine, which contains capsular polysaccharides from multiple serotypes of Streptococcus pneumoniae.

how to polysaccharide vaccines work

by stimulating antibodies that recognise the capsule and help the immune system find and destroy the bacteria.

what immune response is generated by polysaccharide vaccine

T-independent immune response

what can polysaccharide antigens do

directly cross-link B cell receptors without requiring antigen presentation to T helper cells

what is the immune response like as a result in polysaccharide vaccines

Mainly produces IgM antibodies. Because T helper cells are not involved, the immune response is weaker and long-term immune memory is poor.

who are the polysaccharide vaccines particularly poor in

infants and young children

why does this affect children and infants more

the immune system in early life doesn’t respond well to T-independant antigens and vaccines do not generate strong protective immunity and prodice short-lived antibody responses

what are polysaccharide conjugate vaccines

developed to overcome the limitation of pure polysaccharide vaccines.

what are polysaccharide conjugate vaccines composed of

capsular polysaccharide is chemically linked to a carrier protein.

what does the modification of polysaccharide vaccines do

allows the antigen to be processed by antigen-presenting cells and presents to CD4+ T helper cells vis MHC class II molecules

what does the B cell do to the polysaccharide in the conjugate vaccine

takes the whole molecule into the cell

what happens to the protein carrier once in a b cell

it is broken down and its pieces are presented on MCH class II molecules to CD4+ T helper cells

what do the T helper cells do

activate B cells by sending signals and releasing cytokines

what immune response do polysaccharide conjugate vaccines induce

T-dependent immune response that produces strong igG antibodies and long-term memory

what do polysaccharide conjugate vaccines do for children

 

Because conjugate vaccines stimulate T-dependent immunity, they are effective in infants and young children and generate long-lasting protection.

what is a major success of polysaccharide conjugate vaccines

haemophilus influenzae typ b vaccine which reduces invasive HIB worldwide

what did HIB cause

meningitis and pneumonia in young children

what is special about conjugate vaccines

not only protect the individual but reduce nasopharyngeal carriage of the bacteria which decreases transmission and contributes to herd immunity

another example of conjugate

pneumococcal conjugate vaccine which targets several serotypes of Streptococcus pneumoniae

what has the penumococcal conjugate vaccine done

preventing invasive pneumococcal disease in young children and reducing disease in vaccinated populations

comparison

Polysaccharide vaccines produce T-independent responses that are dominated by IgM antibodies and generate little immunological memory. In contrast, conjugate vaccines produce T-dependent responses that lead to class switching to IgG, affinity maturation, and long-term memory B cell formation.

extra benefit of conjugate

Conjugate vaccines also reduce bacterial carriage and therefore contribute to herd immunity, while polysaccharide vaccines have little effect on transmission.

example of when polysaccharide vaccines may not be suitable

 Neisseria meningitidis serogroup B (MenB).

why is a polysaccharide vaccine not suitable for Neisseria meningitidis serogroup B (MenB).

the capsule of Men B is similar to the structure of the humal neural cell adhesion molecule and the immune system recognises it poorly and vaccination could trigger autoimmune reaction

what do Men B vaccines target instead

surface proteins identified through genomic and reverse vaccinology approaches