Abstract
Encapsulated bacteria are responsible for the majority of mortality among neonates and infants. The major components on the surface of these bacteria are polysaccharides which are important virulence factors. Immunity against these components protects against disease. However, most of the polysaccharides are thymus-independent (TI)-2 antigens which induce an inadequate immune response in neonates and infants. The mechanisms that are thought to play a role in the unresponsiveness of this age group to TI-2 stimuli will be discussed. The lack of immune response may be overcome by conjugating the polysaccharides to a carrier protein. This transforms bacterial polysaccharides from a TI-2 antigen into a thymus-dependent (TD) antigen, thereby inducing an immune response and immunological memory in neonates and infants. Such conjugated vaccines have been shown to be effective against the most common causes of invasive disease caused by encapsulated bacteria in neonates and children. These and several other approaches in current vaccine development will be discussed.
Highlights
More than 2.5 million infants die every year from bacteremia, respiratory, and diarrhoeal diseases [1]
MZ B cells with adult features appear after 2 years of life and coincide with the ability to induce an immune response to polysaccharides
With the development of the murine immune system, B cells change from IgMhiIgDlo to IgMloIgDhi and the response to thymus independent (TI)-2 antigens coincided with the appearance of IgD, which takes about one to two weeks in mice [24]
Summary
More than 2.5 million infants die every year from bacteremia, respiratory, and diarrhoeal diseases [1]. The immunologic advantage of this coating is evasion of phagocyte killing, as the coating blocks complement binding and opsonization This can be overcome by C-reactive protein (CRP) binding [3] and the production of antibodies against the polysaccharide [4]. TI2 antigens on the other hand induce a limited immune response in children below two years of age, but older children and adults react to TI-2 antigens with the formation of sufficient antibody production by activated B-cells. TI-2 antigens are bacterial polysaccharides from encapsulated bacteria such as most S. pneumonia serotypes, N. meningitidis, and H. influenza [12] Infection with these bacteria results in a reduced immunological response in neonates and they are at risk [5]. The efficacy and drawbacks of the three main polysaccharideconjugate vaccines will be discussed
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