Not Just Any T Cell Receptor Will Do

AbstractAlthough our structural understanding of T cell recognition has rapidly evolved due to recent crystallographic results, the reality is that detailed answers to many of the most fundamental questions still remain elusive. In this issue, high-resolution insight into the phenomenon of TCR chain bias takes down another brick from the wall

Staphylococcus aureus bound to complement receptor 1 on human erythrocytes by bispecific monoclonal antibodies is phagocytosed by acceptor macrophages

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FTY720 blocks egress of T cells in part by abrogation of their adhesion on the lymph node sinus

Egress of lymphocytes from lymphoid tissues is a complex process in which Gαi-mediated signals play a decisive role. We show here that although FTY720, an agonist of the sphingosine 1-phosphate (S1P)1 receptor, induces S1P1 receptor internalization sufficiently in the presence or absence of Gαi2 or Gαi3, the drug blocks egress of wild-type (WT) and Gαi3-deficent T cells, but not Gαi2-deficient T cells, in both WT and Gαi2-deficient hosts. Intravital imaging of lymph nodes revealed that all three groups of T cells approached and engaged cortical sinusoids similarly in the presence or absence of FTY720. The cells also entered and departed the sinus at an almost identical frequency in the absence of the drug. However, after engagement of the sinus, most WT and Gαi3-deficient T cells retracted and migrated back into the parenchyma in FTY720-treated animals, due to a failure of the cells to establish adhesion on the sinus, whereas Gαi2-deficient T cells adhered firmly on the sinus, which prevented their retraction, facilitating their transmigration of the lymphatic endothelial barrier. These data confirm egress of Gαi2−/− T cells independent of S1P-mediated chemotaxis and failure of FTY720 to close lymphatic stromal channels and argue for the first time, to our knowledge, that FTY720 induces lymphopenia in part by impairing T cell adhesion to the sinus in a manner dependent on Gαi

T-bet-dependent S1P5 expression in NK cells promotes egress from lymph nodes and bone marrow

During a screen for ethylnitrosourea-induced mutations in mice affecting blood natural killer (NK) cells, we identified a strain, designated Duane, in which NK cells were reduced in blood and spleen but increased in lymph nodes (LNs) and bone marrow (BM). The accumulation of NK cells in LNs reflected a decreased ability to exit into lymph. This strain carries a point mutation within Tbx21 (T-bet), which generates a defective protein. Duane NK cells have a 30-fold deficiency in sphingosine-1-phosphate receptor 5 (S1P5) transcript levels, and S1P5-deficient mice exhibit an egress defect similar to Duane. Chromatin immunoprecipitation confirms binding of T-bet to the S1pr5 locus. S1P-deficient mice exhibit a more severe NK cell egress block, and the FTY720-sensitive S1P1 also plays a role in NK cell egress from LNs. S1P5 is not inhibited by CD69, a property that may facilitate trafficking of activated NK cells to effector sites. Finally, the accumulation of NK cells within BM of S1P-deficient mice was associated with reduced numbers in BM sinusoids, suggesting a role for S1P in BM egress. In summary, these findings identify S1P5 as a T-bet-induced gene that is required for NK cell egress from LNs and BM