Human Anti-Carbohydrate repertoire stability and dynamics throughout life

About This Grant

Project Summary Human humoral immunity is mediated by individual B cells endowed with unique antigen receptors. Following antigen engagement, these cells undergo clonal expansion and differentiation into antibody secreting cells (ASC) and memory B cells (Bmem). During immune responses, B cells undergo somatic hypermutation which changes the genes encoding their antigen receptors, a process that when coupled with selection within germinal centers (GC) improves the quality of their B cell antigen receptors (BCR), typically resulting in higher affinity. Following most productive immune responses, expanded clones undergo a contraction phase reducing their numbers. Within the T cell compartment, chronic antigen exposure to antigen maintains increased frequency of clones, resulting in oligoclonality and a reduction of antigen receptor diversity within the global repertoire. Oligoclonal expansions have been observed in the B cell compartment of older adults as well, however the mechanisms responsible for this effect are not known. Serum antibodies reactive with a wide array of carbohydrate determinants are present in all humans, as are B cells reactive with these carbohydrate structures. In contrast to commonly evaluated B cell specificities that encompass antigens encountered intermittently throughout an individual's lifetime, anti-carbohydrate (AC) responses are driven by glycan determinants derived from the commensal microbiota. Accordingly, these antigens are never `cleared' and are continuously available for immune activation. The effect of this chronic antigen exposure on the AC B cell repertoire is not known. As ACAs are the products of B cells that undergo immune activation including GC involvement, somatic mutation, affinity maturation, and differentiation, we hypothesize the AC-repertoire is subjected to recurrent selection promoting the activation and expansion of only a few clones, thereby becoming increasingly oligoclonal in aged adults. The proposal is focused on evaluating the repertoire, Ab binding properties, and the auto-reactive and anti-microbial potential of the AC repertoire directed at the two most frequently targeted carbohydrates in healthy humans across 6 decades of the human life span. We are using state-of-the-art antigen-specific B cell isolation, BCR sequencing, cloning, and expression to evaluate the diversity and binding properties of the human AC repertoire. We are combining these technologies with high-dimensional cytometric antigen arrays, serum Ab fractionation, functional Ab, and transcriptomic assays to determine changes that occur within the ACA-repertoire across the human lifespan. Our efforts to elucidate the effects of chronic antigen exposure of microbial antigens on the human B cell immune system will illuminate mechanisms causing age-associated loss of B cell repertoire diversity and accompanying immunosenescence.