High-dimensional intravital microscopy reveals major changes in splenic immune system during postnatal development.

Spleen is a key organ for immunologic surveillance, acting as a firewall for antigens and parasites that spread through the blood. However, how spleen leukocytes evolve across the developmental phase, and how they spatially organize and interact is still poorly understood. Using a novel combination of selected antibodies and fluorophores to image in vivo the spleen immune environment, we described for the first time the dynamics of immune development across postnatal period. We found that spleens from adults and infants had similar numbers and arrangement of lymphoid cells. In contrast, splenic immune environment in newborns is sharply different from adults in almost all parameters analysed. Using this in vivo approach, B cells were the most frequent subtype throughout the development. Also, we revealed how infections - using a model of malaria - can change the spleen immune profile in adults and infants, which could become the key to understanding different severity grades of infection. Our new imaging solutions can be extremely useful for different groups in all areas of biological investigation, paving a way for new intravital approaches and advances.