Human B-cell receptor specific for Streptococcus pneumoniae type 6B capsular polysaccharide (BCR-Sp6B)

The Human B-cell receptor (BCR) specific for Streptococcus pneumoniae type 6B capsular polysaccharide is a membrane-bound immunoglobulin complex that serves as a critical recognition element in the adaptive immune defense against pneumococcal disease. This receptor is specialized to identify the 6B capsular polysaccharide (CPS), a complex carbohydrate structure that acts as a major virulence factor by protecting the bacterium from host phagocytosis. Upon binding to the 6B CPS antigen—typically delivered through conjugate or polysaccharide vaccines—the BCR initiates a signaling cascade that drives the expansion of specific B-cell clones and their maturation into memory cells and antibody-secreting plasma cells. The resulting secreted IgG antibodies are essential for the opsonization and subsequent clearance of S. pneumoniae by neutrophils and macrophages (PubMed: 15153534). This BCR is a primary functional target for pneumococcal vaccines such as Prevnar 13 and Pneumovax 23, which aim to elicit high-affinity humoral immunity to prevent invasive infections. Research indicates that the human response to the 6B polysaccharide often involves a restricted repertoire of immunoglobulin genes, frequently utilizing the VH3-23 gene segment (PubMed: 18424588). Understanding the structural and genetic basis of this BCR's interaction with the 6B antigen is vital for optimizing vaccine efficacy and addressing the high burden of pneumococcal pneumonia and meningitis in vulnerable populations, including children and the elderly (CDC, 2023).

Other names

Anti-6B B-cell receptorStreptococcus pneumoniae serotype 6B-specific BCR6B-specific surface immunoglobulinAnti-pneumococcal 6B BCR

The BCR binds specifically to the 6B capsular polysaccharide antigen, which consists of repeating units of [->2)-alpha-D-Galp-(1->3)-alpha-D-Glcp-(1->3)-alpha-L-Rhap-(1->4)-D-Rib-ol-(5-P->]. This binding event, particularly when the antigen is conjugated to a carrier protein like CRM197, induces BCR clustering and activates intracellular signaling via the ITAM-containing Ig-alpha/Ig-beta complex, leading to B-cell proliferation, affinity maturation, and differentiation into plasma cells that secrete protective IgG antibodies (PubMed: 15153534, 18424588).