Organ Crosstalk: The Role of Spleen.

In modern medicine, spleen, the largest secondary lymphoid organ, is responsible for red blood cell turnover and immune inductions. The immune system and spleen actively orchestrate local or systemic inflammatory responses under different disease conditions. In traditional Chinese medicine (TCM), spleen contributes to the body integrity and the essence of "Qi"by collaborating in concert with the other organs ("Zang" in TCM). In both realms, spleen is not a solitary organ since it constantly interacts or "crosstalks" with the rest of the body to maintain homeostasis by secreting or responding to signaling molecules from relevant pathways. Since the spleen is involved in organ crosstalk axes, the health status of many other organs can be potentially alluded when we clinically assess the spleen. However, due to structural delicacy and intrinsic disadvantages of conventional pathology such as biopsy, evaluating the spleen status is challenging. To this end, molecular imaging, a non-invasive and efficient modality, emerged as an elegant solution to provide highly precise depiction of spleen phenotypes. It provides a mesoscopic overview of the spleen's physical status and biological processes occurring at the cellular or molecular level in vivo. With the application of molecular imaging modalities, spleen is now appreciated as a key organ involved in the development or progress of various diseases, such as cancer. We expect molecular imaging of the spleen to be a robust starting point for us to understand the molecular level changes underlying physiological observations including spleen crosstalk in TCM and modern medicine, providing mechanistic evidence for phenotypic patterns.