Obesity-driven alterations in humoral B cell immunity

Obesity is a critical global epidemic, a leading cause of preventable death, and a source of skyrocketing health care costs. To improve the health outcomes of patients suffering from the negative consequences of obesity, we must first understand the extent of obesity-induced immunological changes. We recently connected an increase in inflammatory Tbet+CD11c+ B cells in mice and humans to exacerbated metabolic disease (Hägglöf et al, Cell Metabolism 2023). Tbet+CD11c+ B cells accumulate during autoimmune disease and aging, where they are primed for activation specifically in response to innate activation via TLRs and support by T helper cells but their specific inflammatory role during obesity is not well understood. Our preliminary data using high fat diet (HFD) fed mice, shows that 1) Tbet+ B cells expand in spleen, liver, and adipose tissue during obesity and produce IgG2a self-antigen-containing immune complexes; 2) T follicular and peripheral helper cells also expand in spleen and liver during obesity; 3) Tbet+ B cells express high levels of scavenger receptor CD36, which enables increased antigen uptake and enhanced innate signaling, while mice with a B cell restricted deficiency in CD36 develop fewer HFD-induced splenic Tbet+ B cells or T helper cells than controls; 4)eliminating Tbet in B cells during obesity led to increased GC B and T helper cells and improved immune responses to vaccination and infection. Thus, we hypothesize a dual signal paradigm in obesity whereby innate signaling from autoantigens primes Tbet+ B cells for antigen/MHC-recognition and help from T helper cells. Once expanded, we posit that Tbet+CD11c+ B cells inhibit protective GC-based vaccine responses in favor of extrafollicular expansion, which could explain the poor clinical outcomes for vaccinated or infected obese patients. In Aim 1, in vitro and in vivo assays, RNAseq, flow cytometry, adoptive transfer, and immunofluorescent staining in combination with unique transgenic, TLR deficient, lineage-restricted CD36 deficient, and Tbet+ ZTCE reporter mice all us to characterize the signals which define the innate half of the dual-signal paradigm. These studies will also characterize metabolic changes in rare subsets using SCENITH flow cytometry. In Aim 2, we will consider the adaptive half of the dual-signal paradigm and characterize the antigen-presenting requirements, specificity, and nature of T cells which help Tbet+CD11c+B cells during obesity. We will utilize powerful new lines of mice with Cre expression restricted to CD19+ CD11c+ B cells defined by expression of two proteins, created in collaboration with Mark Shlomchik. Pairing these mice with the innovative uLIPSTIC mice will allow us an unbiased identification and characterization of the T helper partners of Tbet+CD11c+ B cells. Finally, these innovative mice provide exquisite tools for querying the use of IL-12 by Tbet+CD11c+ B cells to block vaccine effectiveness in obese mice. These studies will point to a therapeutic strategy for improving quality of life and survival in obese patients. This strategy may be applicable to immunologically related conditions such as aging and autoimmune disease, expanding the therapeutic effect to other clinically vulnerable populations.