PROJECT SUMMARY In the United States, 3 million people have received dental implants, and it is predicted that 500,000 dental implants will be newly placed every year. While dental implants have been a popular option to replace lost teeth, peri-implantitis (PI) is getting more prevalent, affecting 24% of dental implant patients. PI is an oral inflammatory disease causing soft and hard tissue breakdowns around dental implants. PI is challenging to treat because of its irreversible aspect, aggressive progression, and difficulty in cleaning implant surface. The current treatment modalities for PI are mainly limited to surgical interventions, which are generally more invasive, painful, and time- intensive. Moreover, these treatments fail to address the host’s uncontrolled immune response and subsequent microbial dysbiosis. In light of previous studies showing that altered host-microbiome interactions may play key roles in PI pathogenesis, I propose to study immunomodulatory strategies as potential treatment options. The objective of this study is to determine the protective role of the C-C motif chemokine ligand 2 (CCL2) on host- microbiome interactions through direct polarization of macrophages into M2-like anti-inflammatory phenotypes. The murine ligature-induced PI is used as a model for an inflammatory disease where tissue destruction is driven by a breakdown of host-microbe homeostasis. In this study, I hypothesize that the local delivery of CCL2- releasing microparticles (CCL2 MPs) into peri-implant tissues will restore the balance of M1/M2 by polarizing macrophages to M2-like phenotype, create an anti-inflammatory environment, and reverse disease-associated microbial changes in PI. This proposal aims to 1) unravel the immunomodulatory effects of CCL2 on immune cells and their downstream pathways and 2) determine the effects of CCL2 on disease-associated bacteria and microbial dysbiosis. In aim 1, the murine ligature-induced PI model will be used with or without local delivery of CCL2 MPs. Then, single-cell RNA sequencing (scRNA-seq) will be performed to acquire in-depth data about the PI pathogenesis and mechanistic CCL2’s function on immune cells by evaluating pathways and differentially expressed genes. In addition, scRNA-seq data will be complemented by Flow Cytometry data. In aim 2, 16S rRNA gene sequencing analysis on peri-implant plaque buildup will be conducted to assess CCL2’s therapeutic effects on PI-related bacterial species and microbial dysbiosis by modulating the host’s inflammatory response. I will evaluate the total bacterial load and shifts in microbiome compositions with or without CCL2 MPs. The overall goal of this proposal is to challenge the unmet need for effective therapies to treat PI by applying a novel immunomodulatory therapy. Successful completion of this proposed study will expand our understanding of PI pathogenesis and support the therapeutic potential of local immunomodulation in PI.