Stimulation of a memory B cell response does not require primed helper T cells.

The use of universally immunogenic T cell epitopes, such as those identified in tetanus toxin or malaria circumsporozoite protein, could represent a major improvement in the development of synthetic vaccines. However, one limitation of this approach is the lack of T cell cross-reactivity between the vaccine and the pathogen. To determine whether the memory B cell response elicited by immunization with a synthetic peptide containing a B cell epitope linked to a T cell epitope can be restimulated by the same B cell epitope linked to different T cell epitope(s), we used a synthetic peptide which contains non-overlapping B and T cell determinants from hepatitis B surface antigen (HBsAg) of hepatitis B virus (HBV). The results of this study clearly show that primed T cells can increase the antibody response against a B cell epitope linked to the priming T cell determinant. However, the antibody response obtained was weaker than that obtained after two injections of the peptide containing both B and T cell epitopes, showing the important role played by memory B cells in secondary antibody responses. Moreover, a strong antibody response against the B cell epitope was elicited by boosting mice with the B cell epitope linked to a heterologous carrier, thus demonstrating that a strong B cell memory response can be revealed in the absence of primed T cells. These results therefore provide new important information for the design of synthetic or recombinant vaccines.