Intravital Optical Imaging The Dynamics Of Monocytes In Cutaneous Immunity

The skin immune system is the key barrier for the human body to resist external microbial invasion and maintain skin homeostasis.Mobilizing the interstitial migration of leukocyte and subsequent organizing cooperation among these leucocytes in inflamed skin is critical for intelligent and effective response of immune response to foreign antigen challenge.Although the migration strategy of neutrophils?e.g.directional migration?and T cells?e.g.Levy walk?within interstitial space have been thoroughly studied,the behavior of the monocyte is still far from fully investigated till date.When infiltrated into interstitial space,monocytes quickly migrated to sensed inflammatory mediator and communicated with the microenvironment.Therein,they could to be activated to eliminate invasive pathogen or mediate tissue damage.However,the emergence mechanism of monocyte migration and its function-behaviour relationship remain unclear.In addition,it also remains unclear how monocytes are mobilized to amplify inflammatory reactions in T cell-mediated adaptive immunity.Here,we investigate dynamic cellular events in the cascade of inflammatory responses and explore the migration pattern and activation process of monocytes through intravital imaging of a multicolor-labeled murine contact hypersensitivity?CHS?model.Intravital imaging data show that interstitial monocytes migrate in random directions and frequently contact other individuals at 12 hours after hapten challenge.Significantly,cellcell contact promotes monocyte activation,wherein CD11a/ICAM-1 interaction regulates the contact duration and CCR2 mobilize monocyte frequently contact with other individuals.We also found that monocytes formed clusters around hair follicles at 24 hours after hapten challenge in the CHS model.In this process,effector T cells encountered dendritic cells under regions of monocyte clusters and secreted IFN-?,which mobilizes CCR2-dependent monocyte interstitial migration and CXCR2-dependent monocyte cluster formation.We visualized that hair follicles shaped the inflammatory microenvironment for communication among the monocytes,keratinocytes,and effector T cells.After disrupting the T cellmobilized monocyte clusters through CXCR2 antagonization,monocyte activation and keratinocyte apoptosis were significantly inhibited.The main innovations of our research are as follows: 1.We characterize the frequent inter-individual contact among monocytes and verify the contact-dependent pathway for monocyte communication.Cell-cell contact promotes monocyte activation with an increased Ca²⁺ signal and CD11a/ICAM-1 interaction regulates the contact duration in vivo.2.We characterize a T cell-regulated monocyte cluster around hair follicle and reveal the cascade of inflammatory responses and the interactions between innate and adaptive immune response during inflammation in contact hypersensitivity,which provide new insights for our understanding of the processes involved in acquired cutaneous immunity.3.Our results also showed that mobilizing the formation of monocyte clusters is another pathway to stimulate macrophage activation besides the direct stimulation of IFN-?.Mobilizing macrophage interstitial migration and cluster formation is critical for Mon/M? mediating keratinocyte death in the CHS model.