Filamentous phage as a model immunogen for tracking B-cell responses to infection and vaccination (154.30)

Abstract

Abstract Humoral immunity to infection can be categorized into four response stages: (i) innate-like, (ii) early-induced, (iii) adaptive, and perhaps (iv) the response to chronic infection (ChI). The first three stages are mediated by B-cell lineages distinguishable by phenotypic, genetic and functional characteristics. Our analysis of antibodies (Abs) produced during ChI indicates that “ChI Abs” have unique genetic features including high somatic mutation (SM) and usage of distal germline VH genes; ChI is also associated with aberrations in B-cell subsets. Here, we use filamentous phage as a model antigen to determine the genetic features and cellular origins of “ChI Abs” in the mouse. The phage’s surface consists of ~3,000 copies of the major coat protein, pVIII, and a majority of the anti-phage Ab response cross-reacts with a 12-aa peptide comprising the N-terminus of pVIII, allowing easy isolation of phage-specific B cells. After a single immunization, two “waves” of Ab-secreting cells (ASCs) appeared: first, IgM and IgG ASCs expressing proximal unmutated genes, followed by IgG ASCs expressing more distal genes bearing SMs. Phage-specific ASCs and serum IgG increased with repeated immunization, peaking after the fifth immunization and declining thereafter. Thus, we have validated the approach of combining cellular, flow cytometric, serological and immunogenetic analyses to characterize the dynamics of the B-cell response after initial and repeated encounter with antigen.