Production of qualitatively different antibodies by T-bet+ IgM memory cells and plasmablasts

Abstract

Abstract We are investigating the genesis of CD4 T cell-independent T-bet+ IgM+ plasmablasts and memory B cells during intracellular bacterial infection. Although the plasmablasts are generated early during ehrlichial infection, and the memory cells become established within 30 days, it is not known if the populations are related lineally. We showed previously that a high frequency of plasmablast-derived IgM was polyreactive, that is, these IgM bound structurally diverse antigens. Polyreactive IgM were particularly abundant among those Abs that bound the ehrlichial outer membrane protein, OMP-19. Here we addressed whether polyreactivity is also characteristic of memory cell-derived IgM. Antibodies were cloned from sorted CD11c+ T-bet+ IgM memory B cells by single cell Ig sequencing and expressed in HEK cells as chimeric human IgG1. Supernatants were tested by ELISA for reactivity to OMP-19, as well as for double-stranded DNA and insulin. Preliminary data showed that approximately 10% (29 out of 284 samples) of antibodies were OMP-19 specific, but unlike those generated by the plasmablasts, the memory cell-derived antibodies did not exhibit polyreactivity. These data reveal that T-bet+ IgM plasmablasts and memory cells produce distinctly different Igs, which may indicate that the two populations have different origins, or that the populations undergo different selection during their differentiation. Ongoing studies will help resolve these different interpretations.