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Review
. 2021 Sep 21;18(16):3697-3707.
doi: 10.7150/ijms.61080. eCollection 2021.

The Role of the Immune Microenvironment in Bone Regeneration

Ning Yang  1   2 , Yao Liu  1   2
Affiliations
Review

The Role of the Immune Microenvironment in Bone Regeneration

Ning Yang et al. Int J Med Sci. .

Abstract

Bone is an active tissue, being constantly renewed in healthy individuals with participation of the immune system to a large extent. Any imbalance between the processes of bone formation and bone resorption is linked to various inflammatory bone diseases. The immune system plays an important role in tissue formation and bone resorption. Recently, many studies have demonstrated complex interactions between the immune and skeletal systems. Both of immune cells and cytokines contribute to the regulation of bone homeostasis, and bone cells, including osteoblasts, osteoclasts, osteocytes, also influence the cellular functions of immune cells. These crosstalk mechanisms between the bone and immune system finally emerged, forming a new field of research called osteoimmunology. Therefore, the immune microenvironment is crucial in determining the speed and outcome of bone healing, repair, and regeneration. In this review, we summarise the role of the immune microenvironment in bone regeneration from the aspects of immune cells and immune cytokines. The elucidation of immune mechanisms involved in the process of bone regeneration would provide new therapeutic targets for improving the curative effects of bone injury treatment.

Keywords: bone regeneration; immune cell; immune cytokine; immune microenvironment; osteoimmunology.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interest exists.

Figures

Figure 1
Figure 1
Interactions between the immune and skeletal systems. The T cell subsets (Th1, Th2, Th17 and Treg) play an important role in bone repair and regeneration. Th17 cells, known as osteoclastogenesis-supporting T cells, which secret IL-17 to upregulate RANKL expression and induce inflammatory cytokines such as TNF-α and IL-1 from innate immune cells. These cytokines further activate osteoclast precursor cells and inhibite osteoblast function. Contrarily, Th1, Th2 and Treg inhibit osteoclastogenesis by secreting cytokines INF-γ, IL-4, CTLA-4 and IL-10 respectively. B cells antagonistically block the effect of RANKL by secreting OPG and induce osteoclast apoptosis by secreting TGF-β.
See this image and copyright information in PMC

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