Impaired responsiveness to T-cell receptor stimulation and defective negative selection of thymocytes in CCR7-deficient mice

Abstract

The chemokine receptor CCR7 has been implicated in maintenance of thymus morphology and establishment of tolerance to self-antigens. In this study, we provide direct evidence that negative selection of maturing thymocytes is defective in CCR7-deficent mice. Impaired negative selection was observed after TCR/CD3 complex stimulation in vivo as well as in vitro and was prominent in both doublepositive and semimature single positive cells (CD4 ؉ CD8 ؊ CD24 high ). It is noteworthy that thymocytes of CCR7 ؊/؊ mice display defective negative selection in response to endogenous superantigens, demonstrating that the defect also occurs under physiological conditions. Disturbed negative selection was correlated with delayed activation kinetics and decreased calcium flux response of CCR7 ؊/؊ thymocytes after in vitro TCR/CD3 stimulation, suggesting that an impaired response of CCR7 ؊/؊ thymocytes via TCR-mediated signaling is responsible for defective negative selection in these mice. IntroductionCCR7 is a major regulator of the immune system, orchestrating a broad spectrum of fundamental processes ranging from lymphoid organ development to induction of defensive immune responses as well as oral tolerance. [1][2][3] An important role for CCR7 in thymus compartmentalization and coordination of migratory events during thymopoiesis has been recently demonstrated. 4,5 Mice deficient in CCR7 or in its ligands CCL19 and CCL21-ser (plt/plt mice 6,7 ) display altered thymus architecture, impaired T-cell development, and decreased numbers of thymocytes. 4,5 Alterations of the thymus architecture are frequently observed in mice suffering from autoimmunity, such as mice deficient in the transcriptional regulator autoimmune regulator (Aire) and nonobese diabetic (NOD) mice. 8,9 In these strains, autoimmunity correlates with breakdown of central tolerance, although in NOD mice peripheral tolerance seems to be affected as well. [10][11][12] It has been noted previously that lack of CCR7 signaling is associated with the manifestation of autoimmunity to lachrymal and salivary glands. 13 Expanding this view, we recently demonstrated that CCR7-deficient mice in fact display a more generalized autoimmune phenotype affecting several organs. 14 These observations raised the possibility that CCR7-deficiency affects induction of central tolerance.The hallmark of central tolerance is the negative selection of potentially self-reactive thymocytes. This process guarantees the generation of a self-tolerant peripheral T-cell repertoire. The major mechanism of negative selection is clonal deletion. During this process, thymocytes reacting strongly to self-peptide-self-MHC complexes are eliminated. 15,16 Several studies using well characterized in vivo and in vitro models of negative selection suggest that clonal deletion can occur in all developmental stages of thymocytes, including double-negative, double-positive (DP), and singlepositive (SP). 15,[17][18][19][20] However, it is widely accepted that (for thymocytes expressing an MHC class II-restric...

CCR7-mediated migration of developing thymocytes to the medulla is essential for negative selection to tissue-restricted antigens

“…These results indicate that CCR7 directs the migration of SP thymocytes to the medulla. However, a recent report by DavalosMisslitz et al (15) showed that the density of CD4SP thymocytes in the medulla was not reduced in thymus sections of CCR7 Ϫ/Ϫ (ML) mice, thereby questioning the role of CCR7 in the migration of SP thymocytes to the medulla. Accordingly, we reexamined whether CCR7 contributes to the migration of thymocytes to the medulla.…”

Mst1 regulates integrin-dependent thymocyte trafficking and antigen recognition in the thymus

“…GIT2 − / − DP cells are hyper-responsive to chemotactic cues, which bias localization in the cortex, leading to perturbations in the positive selection process 12 . CCR7-deficient mice develop autoimmunity because of defective negative selection [13][14][15][16] . However, the mechanisms by which thymocyte trafficking controls these selection processes are not well understood.…”

Dynamic control of β1 integrin adhesion by the plexinD1-sema3E axis

“…Despite being highly mobile (7), DP thymocytes remain sequestered in the cortex in frequent physical association with thymic epithelial cells (TECs), moving toward the thymic medulla via chemokine guidance only subsequent to TCR stimulation by self-derived peptide/MHC complexes (pMHC) that induce CD69 expression and support cell survival, i.e., positive selection (8,9). CD69 + DP cells differentiate further into CD4 + CD8 − or CD4 − CD8 + singlepositive (SP) thymocytes, translocating to the thymic medulla to complete their maturation (10,11). While traversing the thymus, immature αβ TCR + thymocytes that are strongly self-reactive with pMHC displayed on cortical and medullary TECs (cTECs and mTECs, respectively) are purged from the repertoire before peripheral exportation in a process termed negative selection (12)(13)(14)(15)(16).…”