Protein Interactions in Antibody Diversity

National Institute On Aging

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Abstract

Activation-induced deaminase (AID) not only mutates DNA within the immunoglobulin loci to generate antibody diversity, but it also promotes development of B cell lymphomas. To tame this mutagen, we performed a quantitative high-throughput screen of over 90 000 compounds to see if AID activity could be mitigated. The enzymatic activity was assessed in biochemical assays to detect cytosine deamination and in cellular assays to measure class switch recombination. Three compounds showed promise via inhibition of switching in a transformed B cell line and in murine splenic B cells. These compounds have similar chemical structures, which suggests a shared mechanism of action. Importantly, the inhibitors blocked AID, but not a related cytosine DNA deaminase, APOBEC3B. This first report of small molecules that inhibit AID can be used to gain regulatory control over base editors. Concerning autoimmunity, a distinct B cell population marked by elevated CD11c expression is found in patients with systemic lupus erythematosus (SLE). Cells with a similar phenotype have been described during chronic infection, but variable gating strategies and nomenclature have led to uncertainty of their relationship to each other. We isolated CD11c-hi cells from peripheral blood and characterized them using transcriptome and IgH repertoire analyses. Gene expression data revealed the CD11c-hi IgD+ and IgD- subsets were highly similar to each other, but distinct from naive, memory, and plasma cell subsets. IgH V-gene sequencing analysis showed IgD+ and IgD- CD11c-hi B cells had somatic hypermutation and were clonally related to each other and to conventional memory and plasma cells. The results portray a pervasive B cell population that accumulates during autoimmunity and chronic infection and is refractory to BCR signaling. For antibody responses in mice, compared to males, influenza vaccination of female mice caused greater production of class-switched, somatically-hypermutated antibodies and a more robust germinal center B cell response, leading to more diverse H1N1 antigen recognition and better protection against mutant influenza A viruses. Harnessing methods to improve germinal center B cell responses and frequencies of somatic hypermutation, especially in males, should be considered in the development of universal influenza vaccines.