A role for LFA-1 in delaying T-lymphocyte egress from lymph nodes.

Lymphocytes use the integrin leukocyte function-associated antigen-1 (LFA-1) to cross the vasculature into lymph nodes (LNs), but it has been uncertain whether their migration within LN is also LFA-1 dependent. We show that LFA-1 mediates prolonged LN residence as LFA-1(-/-) CD4 T cells have significantly decreased dwell times compared with LFA-1(+/+) T cells, a distinction lost in hosts lacking the major LFA-1 ligand ICAM-1. Intra-vital two-photon microscopy revealed that LFA-1(+/+) and LFA-1(-/-) T cells reacted differently when probing the ICAM-1-expressing lymphatic network. While LFA-1(+/+) T cells returned to the LN parenchyma with greater frequency, LFA-1(-/-) T cells egressed promptly. This difference in exit behaviour was a feature of egress through all assessed lymphatic exit sites. We show that use of LFA-1 as an adhesion receptor amplifies the number of T cells returning to the LN parenchyma that can lead to increased effectiveness of T-cell response to antigen. Thus, we identify a novel function for LFA-1 in guiding T cells at the critical point of LN egress when they either exit or return into the LN for further interactions.