Cutting edge: the chemokine receptor CXCR3 retains invariant NK T cells in the thymus.

The current model used to define T cell export from the thymus suggests that emigrating lymphocytes seed the peripheral organs as functionally mature cells. This model holds true for the majority of T cells exported from the thymus with the exception of invariant NK T (iNKT) cells. iNKT cells undergo lineage expansion after positive selection and acquire NK receptor expression once fully mature; yet, the majority of mature iNKT cells are retained in the thymus by an as of yet unidentified mechanism. In this study we demonstrate that mature iNKT cells are retained in the thymus by the chemokine receptor CXCR3. We propose that the expression of CXCR3 ligands in the thymic medullary epithelium promotes the chemotactic retention of mature iNKT thymocytes and prevents leakage of iNKT cells into the peripheral circulation.

Application of a new anti-zearalenone monoclonal antibody in different immunoassay formats.

Monoclonal antibodies against zearalenone (ZEA) were raised in mice according to the hybridoma technology and applied in different immunochemical techniques. More specifically, three formats based on the competitive direct enzyme immunoassay principle were developed: an enzyme-linked immunosorbent assay (ELISA), a flow-through gel-based immunoassay column and a flow-through membrane-based immunoassay. In ELISA, the 50% inhibitory concentration (IC50) was 0.8 ng/mL, and the limit of detection for ZEA standard solutions was 0.1 ng/mL. The antibodies showed a high ZEA (100%) and alpha-zearalenol (alpha-ZOL) (69%) recognition, while cross-reactivities with alpha-zearalanol, zearalanone, beta-zearalenol and beta- zearalanol were 42%, 22%, <1% and <1%, respectively. For standard solutions, a cut-off level at 10 ng/mL could be established for the gel- and membrane-based enzyme immunoassays. Assay time of both non-instrumental tests was 25 min for 10 samples. By including a simple sample extraction procedure, the methods were applied to wheat with IC50s in ELISA of 80 and 120 microg/kg (dilution up to 5% and 15% (v/v) of wheat matrix, respectively). The cut-off level of the gel- and membrane-based immunoassays was established at 100 microg/kg. Potentials and limitations of the developed methods were compared. The possible application for multi-mycotoxin analysis of the ELISA method based on a single monoclonal antibody was investigated. Therefore, principal component analysis and partial least squares regression data modelling were used to separate the immunoassay responses of two cross-reactants (ZEA and alpha-ZOL).

Lymphotoxin alpha 1 beta 2: a critical mediator in V alpha 14i NKT cell differentiation.

Lymphotoxin (LT) alpha 1 beta 2, a tumour necrosis factor (TNF) cytokine critically involved in lymphoid organogenesis, is indispensable for the differentiation of V alpha 14i natural killer T (NKT) cells, a lymphocyte subset with important immunoregulatory properties. However, it is not required for the development of conventional T-cells. LT alpha 1 beta 2 signals through the LT beta receptor, which is expressed on non-lymphoid cells. Triggering of this receptor induces a unique signalling cascade leading to the activation of the transcription factor RelB through activation of NF-kappa B inducing kinase. This pathway is required for V alpha 14i NKT cell differentiation as appears from studies in gene-deficient animals. By reciprocal bone marrow chimeras, it was shown that RelB is required in a radiation-resistant host cell or stromal cell for normal V alpha 14i NKT cell development, presumably in the thymic stroma. These stromal cells are not required for the positive selection of these cells but rather play a prominent role in their terminal differentiation. Altogether, these observations underscore the unique developmental requirements of this particular lymphocyte subset.

A unique lymphotoxin {alpha}beta-dependent pathway regulates thymic emigration of V{alpha}14 invariant natural killer T cells.

Natural killer (NK) T cells using an invariant Valpha14 (Valpha14i) T cell receptor rearrangement form a distinct immunoregulatory T cell lineage. Several studies indicated that a NK1.1(-) Valpha14i NKT precursor cell differentiates and expands within the thymus before export to the peripheral tissues occurs. However, little is known about the signals that cause the emigration of Valpha14i NKT cells from the thymus to the periphery. Here we show that signaling of lymphotoxin (LT) alphabeta through the LTbeta receptor (LTbetaR) is indispensable for regulating peripheral but not thymic Valpha14i NKT cell numbers. Homing to and homeostatic proliferation of thymic Valpha14i NKT cells in peripheral organs, however, was not dependent on LTbetaR. Instead, our data indicate that a LTbetaR-expressing thymic stromal cell regulates the thymic emigration of Valpha14i NKT cells but not conventional T cell receptor alphabeta cells.

Ly49 and CD94/NKG2 receptor acquisition by NK cells does not require lymphotoxin-beta receptor expression.

A crucial step in murine natural killer (NK) cell development, mediated by bone marrow stromal cells, is the induction of Ly49 and CD94/NKG2 receptor expression. The signals that regulate Ly49 receptor expression are still largely undetermined. It has been shown that interaction between lymphotoxin alpha1beta2 (LTalpha1beta2) and LTbeta receptor (LTbetaR), expressed on lymphoid progenitor cells and nonlymphoid bone marrow stromal cells, respectively, is important for both quantitative and functional NK cell development. Therefore, we have investigated the role of LT-LTbetaR-mediated signaling in Ly49 and CD94/NKG2 receptor acquisition. We show that the NK receptor repertoire of LTbetaR-/- mice can only be partially analyzed because of the residual 129/Ola mouse genetic background, due to a physical linkage of the LTbetaR locus and the loci encoding the Ly49 and CD94/NKG2 receptors. Therefore, we transferred wild-type B6 lymphoid-committed progenitor cells into LTbetaR-/- mice, which differentiated into NK cells with a normal NK cell receptor repertoire. Also, administration of LTbetaR-immunoglobulin (Ig), which acts as a soluble receptor for LTalpha1beta2, resulted in reduced NK cell percentages but did not influence the Ly49 and CD94/NKG2 receptor acquisition on remaining NK cells. These results indicate that LTbetaR-mediated signals are not required for Ly49 and CD94/NKG2 receptor acquisition.

A vasorelaxing factor is released from mouse retinal tissue.

The present study aimed to demonstrate the release of a retinal relaxing factor (RRF) from the retina of mice and to investigate the identity of the RRF. Ring segments of a mouse aorta were mounted in a small vessel myograph. The relaxing influence of mouse retinal tissue was assessed by placing a retina in close proximity to the precontracted aorta. This elicited reliable and reproducible relaxations in the aorta. Both the nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine and the soluble guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one had no effect on the RRF response. Also the cyclooxygenase inhibitors indomethacin and sodium diclofenac failed to affect the retina-induced relaxations. Acute hypoxia largely enhanced retina-induced relaxations. It is concluded that mouse retinal tissue releases an RRF, that the mouse RRF response is not mediated by NO or prostanoids and that the mouse RRF response is profoundly influenced by hypoxia.