Antibody Diversity Section
Patricia J. Gearhart, Ph.D., Chief
Somatic hypermutation of immunoglobulin genes occurs at a frequency that is a million times greater than mutation in other genes. We have used biochemical and genetic techniques to study this fascinating process that is initiated by activation-induced deaminase (AID). AID is targeted to variable regions in germinal center B cells by transcription. We found that RNA polymerase II accumulated for an extended distance of 1.2 kb from the promoter, along with the Spt5 transcription factor and AID. The data support a model where mutations occur when the initiating form of RNA polymerase is retained. However, it is not known what causes RNA polymerase to pause in variable regions. We are using biochemical and genetic techniques to decipher this enigma.
To study aging, we sequenced VH and VK rearranged genes from old mice and found that the age-associated B cell subset had a heterogeneous repertoire with significant somatic hypermutation. The results indicate that these cells are antigen-experienced and accumulate over time to diverse antigens. We are now defining how old B cells differ functionally and transcriptionally from their young counterparts.
To study inflammation, we are characterizing the role of B cells in atherosclerosis. Using mouse and human tissues, we demonstrated that antibodies to oxidized low density lipoproteins prevent disease, and antibodies to self-proteins increase inflammation. We then cloned B cells produced at the site of aortic plaques, which will be used to identify novel antigens. The long-term goal is to create potential vaccines for disease prevention.
- Targeting of activation-induced deaminase to variable regions by transcription.
- Characterization of B cells associated with aging.
- Role of B cells and antibodies in atherosclerosis.
Findings and Publications
Castiblanco, D.P., Maul, R.W., Russell Knode, L.M., and Gearhart, P.J.: Co-stimulation of BCR and Toll-like receptor 7 increases somatic hypermutation, memory B cell formation, and secondary antibody response to protein antigen. Frontiers Immunol. 8:1833, 2017 (PMC ID# 5742111).
Pape, K.A., Maul, R.W., Dileepan, T., Paustian, A.S., Gearhart, P.J., and Jenkins, M.K.: Naïve B cells with high-avidity germline-encoded antigen receptors produce persistent IgM+ and transient IgG+ memory B cells. Immunity 48: 1135-1143, 2018 (PMC ID# 6052797).
Zanotti, K.J., Maul, R.W., Yang, W., and Gearhart, P.J.: DNA breaks in Ig V regions are predominantly single stranded and are generated by UNG and MSH6 DNA repair pathways. J. Immunol. 202: 1573-1581, 2019 (PMC ID# 6382588).
Russell Knode, L.M., Park, H.-S., Maul, R.W., and Gearhart, P.J.: B cells from young and old mice switch isotypes with equal frequencies after ex vivo stimulation. Cell. Immunol. 345:103966, 2019 (PMC ID# 6832841).