Upon the infection with pathogens, MHC class II intermediate (IIint) immature dendritic cells (DCs) in peripheral tissues mature into MHC class II high (IIhigh) mature DCs, and migrate to the draining lymph nodes (dLNs) for stimulating antigen-specific T cells to initiate adaptive immune responses. However, details of phenotypes and information about migration and proliferation of migratory DCs from immune site in the dLNs remain unknown.
After immunization with CFA/OVA of footpads of photoconvertible protein KikGR knock-in mice, class IIhigh DCs and class IIint DCs increased in the popliteal dLNs along with the enlargement of dLNs. To track migratory DCs from immunized footpads, immunized footpads were exposure to violet light to mark DCs as KikGR-Red. Twenty-four hours after photoconversion, almost 40% of class IIhigh DCs in dLNs were KikGR-Red phenotype, and similar results were obtained for more than 14 days after immunization, suggesting class IIhigh DCs continuously migrated from immunized site. In addition, unexpectedly, KikGR-Red class IIint DCs (almost 10% in total class llint DCs) were detected in the dLNs. KikGR-Red class IIint DCs expressed low level of co-stimulatory molecules, CD86 as well as CD40 as similar to LN-resident DCs. While, expression of CCR7 and PD-L2 on KikGR-Red class IIint DCs was higher than those on LN-resident DCs. These results suggested that class IIint DCs migrated from immunized site to the dLN during immune responses, and they are immature and tolerogenic DC phenotype. Furthermore, we analyzed migration and proliferation simultaneously and found that class IIint DCs migrated from immunized sites proliferated in the dLNs.
These results suggest that migratory class IIint DCs are likely to negatively regulate immune responses for a long time.