Quantitative Measurement of Naive T cell Association with Dendritic Cells, FRCs, and Blood Vessels in Lymph Nodes

T cells play a vital role in eliminating pathogenic infections. To activate, naive T cells search lymph nodes(LNs) for dendritic cells(DCs). Positioning and movement of T cells in LNs is influenced by chemokines including CCL21 as well as multiple cell types and structures in the LNs. Previous studies have suggested that T cell positioning facilitates DC colocalization leading to T: DC interaction. Despite the influence chemical signals, cells, and structures can have on naive T cell positioning, relatively few studies have used quantitative measures to directly compare T cell interactions with key cell types. Here we use Pearson correlation coefficient (PCC) and normalized mutual information (NMI) to quantify the extent to which naive T cells spatially associate with DC, fibroblastic reticular cells (FRC), and blood vessels in LN. We measure spatial associations in physiologically relevant regions. We find that T cells are more spatially associated with FRCs than with their ultimate targets, DCs. We also investigated the role of a key motility chemokine receptor, CCR7, on T cell colocalization with DCs. We find that CCR7 deficiency does not decrease naive T cells association with DCs, in fact, CCR7-/- T cells show slightly higher DC association compared with wild type T cells. By revealing these associations, we gain insights into factors that drive T cell localization, potentially affecting the timing of productive T: DC interactions and T cell activation.