6. Streptococcus pneumoniae, also called pneumococcus are
lancet-shaped, gram-positive diplococci.
The pneumococcal cell wall surface is covered by a
polysaccharide capsule .
The polysaccharide capsule is an essential virulence factor
and means of evading the immune system by resisting
phagocyte killing.
Type-specific antibody to capsular polysaccharide is
protective. 6
7.
8. Colonization:
o S. Pneumoniae is common inhabitant of the respiratory tract
and may be isolated from the nasopharynx.
o Humans may carry the bacteria without being infected
(asymptomatic carriers) , but may still pass on the bacteria to
others .
Transmission:
Person-to-person via respiratory droplets/secretions OR
Autoinoculation in asymptomatic carriers .
8
S. Pneumoniae: Transmission & colonization
13. Invasive
Non-invasive
1. WHO. Acute Respiratory Infections (Update September 2009). 2. Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine Preventable
Diseases. The Pink Book. 11th Edition. May 2009.
26. + =
Conjugate vaccine
The conjugation of a polysaccharide to a carrier protein leads to the interaction with
T cells resulting in the release of functional antibodies and production of
memory B cells
Polysaccharide
antigens
Immunogenic
carrier protein
B cell
Plasma cell
T-independent
Presentation
T cell B cell
Memory B cell
T-dependent
Plasma cell
27.
28. 28
Both of them elicit a B-cell-mediated immune response, but only
PCV13 produces a T-cell dependent response, which is essential for
maturation of the B-cell response and development of
immune memory.
