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ems_954 ems_954
wrote...
7 years ago
 Caleb has a lung infection caused by the bacterium Streptococcus pneumoniae, an extracellular pathogen. What type of adaptive immune response (humoral or cell mediated) will Caleb’s immune system have to the bacteria?
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wrote...
Educator
7 years ago
Adaptive immune response is an aquired immune response developed by the body after infected by the pathogen. Adaptive immunity provides protection from a particular threat. It involves "cell mediated immune responce (CMI) and anti-body mediated immune (AMI) responces mediaed by B and T lumphocytes mainly. This immune response prevents or supress the growth of microorganism.

When Streptococcus pnewmonia infects a person, adaptive immune response operate and it also generates memory cells along with antobodies, that recognise the organism and stimulate the release of anti-bodies immediately after its second infection. Particulary anti-bodies are generated against its capsular polysaccharides (caps-PS) are generated. Thus, anti-bodies against a particular pathogen are producesd by adaptive immune response by our body, infact this is the basis of synthesis of vaccines.
wrote...
Staff Member
7 years ago
Streptococcus pneumoniae is the second commonest cause of fatal bacterial infection worldwide. Most deaths are due to pneumonia, which when severe is often associated with septicaemia.

Nasopharyngeal colonisation with S. pneumoniae is nearly universal in infants, with carriage rates reaching 90% but then rapidly falling to 10% in late childhood and adults.

Although S. pneumoniae infections are common, the majority of colonised individuals do not develop disease suggesting there are robust natural mechanisms of immunity.

These will include physical defences and innate immune responses, but the proportionally greater fall in S. pneumoniae disease rates compared to carriage rates after the first year of life suggests adaptive immune responses also have a role.

S. pneumoniae colonisation in humans can induce anti-capsular antibodies, and by extension from vaccine data these were previously thought to be the main mechanism of naturally acquired adaptive immunity to invasive infectio.

However, in human models S. pneumoniae nasopharyngeal colonisation induces mainly anti-protein rather than anti-capsular antibody responses .

Recent publications have shown that mice colonised with mutant strains of S. pneumoniae, including unencapsulated strains, develop anti-protein antibody responses.

Colonisation-induced protection was not seen in MHCII?/? mice, suggesting an important role for CD4+ helper T-cells. CD4 T-cells may assist protective adaptive immune responses by providing T-cell help towards B-cell antibody production and/or through memory T-cell responses recalled during infectious challenge.

Recall responses to bacterial antigens by human T-cells implies priming during natural exposure. Such cells include Th17-cells, capable of producing large amounts of the cytokines IL-17A and IL-22 which facilitate cellular recruitment to sites of infection and enhance the release of antimicrobial products from local epithelium.

Th17 responses induced through immunisation can protect against challenge with other respiratory pathogens including Bordetella pertussis and Mycobacterium tuberculosis .

S. pneumoniae nasopharyngeal colonisation of mice is known to elicit a Th17-cell response that assists primary clearance of S. pneumoniae from the nasopharynx and inhibits recolonisation.

Furthermore, nasal immunisation with killed S. pneumoniae or purified pneumococcal proteins can also elicit a Th17-cell response capable of protecting against subsequent colonisation.
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