Flashcards in Path Lab - Asplenia Deck (23)
Most bacteria have an outer layer of polysaccharide. What are the 3 different layer types of polysaccharide?
a) glycocalyx – very thin layer
b) capsule – thicker layer
c) slime - Amorphous polysccharide extending into the environment
How is capsular serotyping done?
In a given species of encapsulated bacteria, there are generally a number of different antigenic types, determined by the type and the arrangement of the polysaccharides.
Specific antibodies raised in animals (eg. mice, rabbits) can be used in the serotyping of encapsulated bacteria by observing their agglutination when mixed with different antibodies (antisera).
How many capsular serotypes are there for Neisseria meningitidis?
How many capsular serotypes are there for Streptococcus pneumoniae?
How many capsular serotypes are there for Haemophilus influenzae?
6 encapsulated serotypes. Other non encapsulated serotypes exist
Name the serotypes for Neisseria meningitidis
Name the serotypes for Haemophilus influenzae
h serotypes of N. meningitidis cause most disease in Australia?
B and C. B accounts for most cases, and C accounts for about 1/3.
Which groups of people in the Australian population are most predisposed to serious infection with S. pneumoniae?
- Adults over 65
- children under 2
- immunocompromised people
Which serogroup of H. influenzae is the most virulent, and why is it now an uncommon pathogen in Australia?
- type B (Hib)
What categories of vaccines are there?
1. Live (Attenuated) vaccines
2. Inactivated vaccines – contain one or a few components of the organism, i.e. polysaccharide. It cannot replicate.
What vaccines are available in Australia for Neisseria meningitidis?
- meningococcal B vaccine Bexsero® available on private market
- meningococcal ACWY vaccine available on prescription for travellers
- Meningococcal C vaccination is recommended as part of routine childhood immunization – given at 12m
What vaccines are available in Australia for Streptococcus pneumonia?
Pneumococcal vaccine is recommended as part of routine childhood immunisation, – given at 2m, 4m, 6m. Booster at 12m and 4 years.
What vaccines are available in Australia for Haemophilus influenzae?
Hib vaccination is recommended as part of routine childhood immunization – 2,4,6 months. Booster at 12 months.
What are some of the functions of bacterial capsules?
• permeability barrier
• adherence to surfaces
• carbohydrate reserve for subsequent metabolism
• resistance to phagocytosis by cells of the immune
What are the two categories of phagocytosis attachment?
• unenhanced attachment - earlier, faster
Bacteria with PAMPS bind with pattern recognition receptor on phagocyte, which activates phagocyte causing phagocytosis.
• enhanced attachment - slightly delayed
- more efficient
Done through opsonisation. Bacteria are coated with opsonsins which makes phagocytosis.
In bacterial phagocytosis, antibodies or the C3b component of the complement system can act as opsonisers for enhanced attachment. What are the two different receptors for the IgG antibody and C3b?
- IgG antibody – the Fc receptor
- C3b – CR1 receptor
Why do asplenic patients have problems with bacteria with capsules?
The early immune response to bacterial capsules is opsonisation with C3b. These can then be phagocytized in the spleen. C3b production is also enhanced by IgM from splenic marginal zone B-cells.
Antibodies directed against capsular antigens occur later in the immune response, however asplenic patients may not survive this long.
What do marginal zone B cells do?
- encounter antigens in the marginal zone of the spleen
- rapid production of IgM and IgG antibodies in a T cell-dependant manner
- these exist only in the spleen
- IgM binds to polysaccharide capsule
What do follicular B cells do?
- encounter antigens in germinal centres of follicles in lymphoid tissue
- require T cell help to produce antibodies that are high affinity and isotype switched, as well as memory B cells.
What causes of asplenia and hyposplenism?
- sickle cell disease
- inflammatory bowel disease
- coeliac disease
- allogeneic bone marrow transplantation
Describe the vaccination schedule recommended for asplenic patients, or those facing elective splenectomy
Persons with an absent or dysfunctional spleen are at a life-long increased risk of fulminant bacterial infection, most notably invasive pneumococcal disease (IPD) - Pneumococcal, meningococcal, Hib and influenza vaccination are particularly recommended for all persons with asplenia
See http://www.immunise.health.gov.au/internet/immunise/publishing.nsf/Content/Handbook10-home~handbook10part3~handbook10-3-3 for detailed schedule (it’s complex, depending on age and vaccination history)