L-selectin expression on thymic emigrants defines two distinct tissue-migration pathways

Area of Science:

• Immunology
• Developmental Biology
• Cell Biology

Background:

• Recent thymic emigrants (RTEs) are T cells recently exported from the thymus.
• Understanding RTE homing is crucial for adaptive immunity.
• Lambs provide a valuable model for studying T cell development and migration.

Purpose of the Study:

• To investigate the phenotype and homing receptor expression of RTEs in neonatal lamb blood, spleen, and lymph nodes.
• To compare the migration patterns of T cell subsets to different lymphoid organs.
• To explore the role of L-selectin in RTE homing to the spleen versus lymph nodes.

Main Methods:

• In situ labeling of thymocytes with fluoroscein isothiocyanate (FITC).
• Flow cytometric analysis of RTEs in blood, spleen, and lymph nodes.
• Assessment of L-selectin expression on alphabeta and gammadelta T cell receptor (TCR+) subsets.

Main Results:

• Significant differences observed in the proportions of CD4+, CD8+, and gammadelta TCR+ RTEs exported to spleen versus lymph nodes.
• Spleen showed enrichment of CD8+ and gammadelta TCR+ RTEs, while lymph nodes were enriched in CD4+ RTEs.
• RTEs homing to lymph nodes predominantly expressed L-selectin, whereas a considerably lower proportion of spleen-homing RTEs expressed L-selectin.

Conclusions:

• RTEs exhibit distinct phenotypic profiles and homing receptor expression depending on their destination organ (spleen vs. lymph nodes).
• The low expression of L-selectin on spleen-homing RTEs suggests unique homing receptor specificities for splenic T cell migration.
• These findings highlight differential migration strategies for T cells entering circulation via the spleen compared to lymph nodes.