Development of an Inducible Conditional Gene Deletion Mouse Model to Study Plasma Cell Development and Longevity

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Project Summary/Abstract Aging is associated with an overall decline in the adaptive immune response with a bulk of the research focusing on the deficiencies surrounding not only the function, but also the generation, of naive B and T lymphocytes. In contrast, not much is known about how aging alters the functionality of plasmacytes. Plasmacytes represent the terminal differentiation step of mature B cells and consist of both short-lived, proliferative plasmablasts (PBs) and more mature, non-proliferative plasma cells (PCs). These cells are key facilitators of humoral immunity through their robust production of antibodies (Abs) as well as their potential to be long-lived. In humans, this longevity can span decades. Historically, these cells have been considered nothing more than Ab factories; however, recent work has demonstrated the ability of plasmacytes to regulate a variety of physiological processes. In the context of aging, PCs have been shown to evolve a pro-inflammatory phenotype and be key drivers of the increased bone marrow (BM) myelopoiesis normally observed in the elderly. This is in part through the PC-dependent expansion in the numbers of hematopoietic stem cells and myeloid progenitors which has been linked to the elevated incidence of myeloid leukemias in the aged population. More recently, we have identified a sex disparity that exists in regard to PB/PC populations within the young thymus (THY) in which 3 months old female mice have significantly higher numbers of these cells compared to males. Interestingly enough, these THY PBs/PCs express key proteins required for THY T cell selection and their numbers significantly correlate with overall THY cellularity. Similar to BM, we have observed changes in THY PB/PC populations in the context of aging. In particular, male mice accumulate THY PBs/PCs with age while numbers remain constant in females. This is in contrast to BM and spleen (SPL) where PBs/PCs increase with age in both sexes. Thus, understanding how PBs/PCs age will allow us to better evaluate their role(s) in adaptive immune responses in the elderly as well as their evolving repertoire of Ab-independent functions. Ultimately, this may lead to the development of therapies that alter PB/PC behavior and promote increased healthspan in aged individuals. It is currently difficult to identify bona fide long-lived, or aged, plasmacytes. While a variety of cell surface markers have been shown to identify plasmacytes, these determinants do not necessarily correlate with longevity but rather maturity. Alternatively, cell labeling techniques rely on efficient labeling of upstream B cells and label retention in the subsequently generated PBs/PCs. In some instances, detection of these labels requires cell permeabilization thus eliminating the ability to further study living, aged PBs/PCs. Aim 1 focuses on the development of an inducible system to indelibly mark, or timestamp, plasmacytes using a fluorescence reporter thus facilitating the ability to assess population dynamics and potentially isolate cells of various ages. Aim 2 will demonstrate the feasibility of this reporter system to specifically determine differential population turnover and/or maintenance in female versus male THY plasmacytes.