The Immunoglobulin M Response to Pneumococcal Polysaccharide Vaccine Is Sufficient for Conferring Immunity.

In mice, pneumococcal polysaccharide (PPS) vaccines generate antigen-specific immunoglobulin M (IgM) and immunoglobulins G1, G2, and G3. Antibody and complement-dependent opsonophagocytosis correlates with the protection induced by PPS vaccines in vivo. Since IgM is a very efficient immunoglobulin isotype in activating the complement system, we evaluated whether anti-PPS IgM alone is sufficient to confer protective immunity to Streptococcus pneumoniae.

Terminal Deoxynucleotidyl Transferase Is Not Required for Antibody Response to Polysaccharide Vaccines against Streptococcus pneumoniae and Salmonella enterica Serovar Typhi.

B cell antigen receptor (BCR) diversity increases by several orders of magnitude due to the action of terminal deoxynucleotidyl transferase (TdT) during V(D)J recombination. Unlike adults, infants have limited BCR diversity, in part due to reduced expression of TdT. Since human infants and young mice respond poorly to polysaccharide vaccines, such as the pneumococcal polysaccharide vaccine Pneumovax23 and Vi polysaccharide (ViPS) of serovar Typhi, we tested the contribution of TdT-mediated BCR diversity in response to these vaccines.

An Unmutated IgM Response to the Vi Polysaccharide of Typhi Contributes to Protective Immunity in a Murine Model of Typhoid.

T cell-dependent B cell responses typically develop in germinal centers. Abs generated during such responses are isotype switched and have a high affinity to the Ag because of somatic hypermutation of Ab genes. B cell responses to purified polysaccharides are T cell independent and do not result in the formation of bona fide germinal centers, and the dominant Ab isotype produced during such responses is IgM with very few or no somatic mutations.