Clinical implications of the specialised B cell response to polysaccharide encapsulated pathogens
- aMRC Centre for Immune Regulation, University of Birmingham Medical School, Edgbaston, Birmingham, UK, bDepartment of Paediatric Nephrology, Hospital San Rafael, Madrid, Spain, cCanberra Clinical School, University of Sydney and The Canberra Hospital, Woden, ACT, Australia
- Dr Matthew Cook, Canberra Clinical School, University of Sydney, PO Box 11, Woden, ACT, Australia, 2606
- Received 23 January 2001
- Accepted 6 March 2001
Polysaccharide encapsulated human pathogens
Box 1: Summary of main points
Encapsulated bacteria (meningococci, pneumococci, and H influenzae type b) are major causes of respiratory and meningeal infections in infancy worldwide.
Factors that predispose to recurrent infection with encapsulated organisms reflect the importance of B cell receptor signalling and production of complement fixing, opsonising IgG antibodies for host defence against these pathogens.
Investigation of patients with recurrent infection with encapsulated bacteria hinges on identification of defects in antibody production (specific B cell defects, hyposplenism) and opsonisation defects (complement deficiency).
Capsular polysaccharide antigens evoke type 2 thymus independent (TI-2) antibody responses but fail to generate conventional B cell memory.
Antibody unresponsiveness to TI-2 antigens can be overcome by inducing T cell help for responses to polysaccharide antigens (for example, with conjugate vaccines).
Microbiology of encapsulated bacteria
Polysaccharide capsules confer virulence, in part because they enable bacteria to evade adaptive and specific immune defence mechanisms.2 …