Vanadate and pervanadate (the complexes of vanadate with hydrogen peroxide) are two commonly used general protein-tyrosine phosphatase (PTP) inhibitors. These compounds also have insulin-mimetic properties, an observation that has generated a great deal of interest and study. Since a careful kinetic study of the two inhibitors has been lacking, we sought to analyze their mechanisms of inhibition. Our results show that vanadate is a competitive inhibitor for the protein-tyrosine phosphatase PTP1B, with a K i of 0.38 ؎ 0.02 M. EDTA, which is known to chelate vanadate, causes an immediate and complete reversal of the inhibition due to vanadate when added to an enzyme assay. Pervanadate, by contrast, inhibits by irreversibly oxidizing the catalytic cysteine of PTP1B, as determined by mass spectrometry. Reducing agents such as dithiothreitol that are used in PTP assays to keep the catalytic cysteine reduced and active were found to convert pervanadate rapidly to vanadate. Under certain conditions, slow time-dependent inactivation by vanadate was observed; since catalase blocked this inactivation, it was ascribed to in situ generation of hydrogen peroxide and subsequent formation of pervanadate. Implications for the use of these compounds as inhibitors and rationalization for some of their in vivo effects are considered.Protein-tyrosine phosphorylation plays a central role in regulating a variety of fundamental cellular processes (1-3). The tyrosyl phosphorylation state of a protein in the cell reflects the balance between the competing activities of the protein-tyrosine kinases and the protein tyrosine phosphatases (PTPs).

Thymic stromal lymphopoietin (TSLP) is a cytokine that promotes CD4+ T cell homeostasis. We now demonstrate that TSLP is required to mount a normal CD4+ T cell–mediated inflammatory response. TSLP acts directly on naive, but not, memory CD4+ T cells, and promotes their proliferation in response to antigen. In addition, TSLP exerts an effect indirectly through DCs to promote Th2 differentiation of CD4+ T cells. Correspondingly, TSLP receptor (TSLPR) knockout (KO) mice exhibit strong Th1 responses, with high levels of interleukin (IL)-12, interferon-γ, and immunoglobulin (Ig) G2a, but low production of IL-4, -5, -10, -13, and IgE; moreover, CD4+ T cells from these animals proliferate less well in response to antigen. Furthermore, TSLPR KO mice fail to develop an inflammatory lung response to inhaled antigen unless supplemented with wild-type CD4+ T cells. This underscores an important role for this cytokine in the development of inflammatory and/or allergic responses in vivo.

Thymic stromal lymphopoietin (TSLP) signals via a receptor comprising the interleukin (IL)-7 receptor α chain and a distinctive subunit, TSLP receptor (TSLPR), which is most related to the common cytokine receptor γ chain, γc. We have generated TSLPR knockout (KO) mice and found that although these mice had normal lymphocyte numbers, γc/TSLPR double KO mice had a greater lymphoid defect than γc KO mice. This indicates that TSLP contributes to lymphoid development and accounts for some of the residual lymphoid development in γc KO mice and presumably in patients with X-linked severe combined immunodeficiency. Injection of TSLP into γc KO mice induced the expansion of T and B cells. Moreover, sublethally irradiated TSLPR KO mice showed weaker recovery of lymphocyte populations than wild-type (WT) littermates, even when neutralizing anti–IL-7 antibodies were injected. Interestingly, TSLP preferentially stimulated the proliferation and survival of CD4+ single positive thymocytes and peripheral T cells in vitro. Additionally, CD4+ T cells from TSLPR KO mice expanded less efficiently than WT CD4+ T cells in irradiated hosts, and TSLP preferentially expanded CD4+ T cells both in vitro and in vivo. Thus, as compared with other known cytokines, TSLP is distinctive in exhibiting a lineage preference for the expansion and survival of CD4+ T cells.

There are characteristic abdominal findings in patients with LAM that, in conjunction with the classic thin-section CT finding of pulmonary cysts, are useful in establishing this diagnosis.