Differential Contribution of Chemotaxis and Substrate Restriction to Segregation of Immature and Mature Thymocytes

Abstract

SUMMARY T cell development requires sequential localization of thymocyte subsets to distinct thymic microenvironments. To address mechanisms governing this segregation, we used 2-photon microscopy to visualize the migration of purified thymocyte subsets in defined microenvironments within thymic slices. Double-negative (CD4−8−) and double-positive (CD4+8+; DP) thymocytes were strictly confined to cortex where they moved slowly without directional bias. DP cells accumulated and migrated more rapidly in a specialized inner-cortical microenvironment, but were excluded from the medulla by an inability to migrate on medullary substrates. In contrast, CD4 single-positive (SP) thymocytes migrated directionally towards the medulla, where they accumulated and moved very rapidly. Our results reveal a requisite two-step process governing CD4 SP medullary localization: the chemokine receptor CCR7 mediated chemotaxis of CD4 SP cells towards the medulla, whereas a distinct pertussis-toxin sensitive pathway was required for medullary entry. These findings suggest that developmentally regulated responses to both chemotactic signals and specific migratory substrates guide thymocytes to specific locations in the thymus as they mature.

Distinct phases in the positive selection of CD8+T cells distinguished by intrathymic migration and T-cell receptor signaling patterns

“…Preselection DP thymocytes initially localize to the cortex (Fig. 2 F and G), consistent with a previous report (25). After 24 h of culture, however, the majority of OT1 transgenic thymocytes are found in the medulla.…”

“…Intriguingly, we observe a dip in CD69 levels at 12 h, a time point that corresponds to the change in chemokinereceptor expression and migration to the medulla. Thus, thymocytes may "take a break" from TCR signaling as they undergo rapid, directional migration to the medulla (22,25). Indications of biphasic TCR signaling were also reported in another synchronized model for OT1 positive selection, albeit with different kinetics (25).…”

αPIX RhoGEF Supports Positive Selection by Restraining Migration and Promoting Arrest of Thymocytes

“…In the medulla, thymocyte migration is impaired by blocking LFA-1 integrin or by deleting its ligand ICAM-1 (7). Additional factors known to influence localization of thymocytes to the cortex or medulla include chemokines, substrate, and contact with stromal cell "highways" (8,9).…”

B cells within germinal centers migrate preferentially from dark to light zone

“…One of the central questions in this field is whether migration is best described as a (persistent) random walk or whether directed or confined migration is involved, because this is important for our understanding of how cells manage to carry out their functions. Examples of persistent random walk include the migration of T cells, B cells, and plasma cells in lymph nodes (2, 6-8) and of effector T cells migrating in tumors (9), whereas nonrandom migration has for instance been discovered in antigen-engaged B cells moving toward the T zone boundary early in a B-cell response (10), CD8 + T cells being attracted toward "licensed" dendritic cells (11)(12)(13)(14), neutrophil movement in skin (15, 16), and during thymocyte maturation (17,18).In some applications, it is controversial whether migration is best described as random or not, and a prime example is B-cell migration in germinal centers (GCs). At these sites, B lymphocytes mature by somatic hypermutation and clonal selection of the mutants that produce antibody of high affinity.…”