Deciphering The Effect of Xenobiotic Exposure on The Immunobiology of Human Mesenchymal Stem Cells & Their Interaction with Dendritic Cells

Abstract

Mesenchymal Stromal Cells (MSCs) are nonhematopoietic multipotent stem cells that possess a myriad of immunomodulatory and regenerative functions and thus maintain immune physiology and tissue homeostasis in the body. MSCs primarily carry out these functions through intercellular immune interactions involving paracrine secretion of secretory factors such as cytokine, chemokines, and growth factors. Previous study has extensively shown that MSCs display immunosuppressive properties on immune cells of lymphoid lineage; however, MSC’s interactions with cells of myeloid lineage such as dendritic cells require further research. Furthermore, given the central role of dendritic cells in immunity as antigen-presenting cells and the bridge between the innate and adaptive immune systems, it is important to understand how disruptions in the interactions between MSCs and dendritic cells can have implications on immune physiology. This project seeks to address this lack of knowledge by 1) identifying the interactions between human bone marrow derived MSCs and two circulating dendritic cells subtypes (plasmacytoid and myeloid) and by 2) defining the functionality of human bone marrow derived MSCs upon exposure to atrazine. MSC and dendritic cell interactions were investigated by conducting MSC and peripheral blood mononuclear cell (PBMCs) co-cultures under TLR7 or TLR4 stimulation. The presence of MSCs and TLR7 stimulation showed no effects on the function of the plasmacytoid dendritic cell subset. Contrarily, the presence of MSCs and TLR7 stimulation led to a decrease in maturation in the myeloid dendritic cell subset, as measured by CD83 expression using flow cytometry. Interestingly, MSCs present in a co-culture and TLR4 stimulation led to an increase in maturation in the myeloid dendritic cell subset. Secretome analysis of stimulated MSCs using multiplex assays suggests that secretory factors may be the reason for the results seen. Disruptions to MSC immune interactions were investigated by exposing MSCs to the xenobiotic herbicide atrazine at a range of dosages and for various durations of time. Cells were analyzed using an assay matrix comprising of MTT assays, flow cytometry, and multiplex assays. Atrazine was shown to affect MSC metabolic viability, size and granularity in a dose and time dependent manner. Atrazine exposure also modulates certain immunomodulatory and angiogenic secretory factors. Furthermore, atrazine exposure attenuates MSC responsiveness to exogenous cues, namely IFNγ. These results provide the context necessary in understanding how xenobiotic disruptions from atrazine exposure can affect immune interactions between MSCs and circulating dendritic cells.