The CD45 family of transmembrane protein-tyrosine phosphatases plays a critical role in T cell activation signaling by regulating the tyrosine phosphorylation of protein-tyrosine kinases and their substrates. Multiple alternatively spliced CD45 isoforms, differing only in their extracellular domains, are differentially expressed by subsets of T cells with distinct functional repertoires. However, the physiological function of the various isoforms remains elusive. Using a novel panel of Jurkat T cell clones that uniquely express either the smallest (CD45(0)) or the largest (CD45(ABC)) isoform, we previously demonstrated CD45 isoform-specific differences in interleukin-2 secretion and tyrosine phosphorylation of Vav. We now demonstrate differential activation-induced tyrosine phosphorylation of a 76-kDa Vav-associated protein (pp76) by cells expressing distinct CD45 isoforms. The tyrosine phosphorylation of Vav and associated pp76 follow parallel kinetics. pp76 interacts with the SH2 and SH3 domains of Vav. We have identified pp76 as SLP-76, a recently cloned Grb2-binding protein. After activation with anti-CD3, CD45(ABC) transfectants demonstrate increased tyrosine phosphorylation and physical association of SLP-76 with Vav compared to transfectants expressing CD45(0). These results establish a novel physical link between Vav and SLP-76 that is differentially regulated by CD45 isoform expression.

The CD45 family of transmembrane protein-tyrosine phosphatases plays a crucial role in the regulation of lymphocyte activation by coupling activation signals from antigen receptors to the signal transduction apparatus. Multiple CD45 isoforms, generated through regulated alternative mRNA splicing, differ only in the length and glycosylation of their extracellular domains. Differential distribution of these isoforms defines subsets of T cells having distinct functions and activation requirements. While the requirement for the intracellular protein-tyrosine phosphatase domains has been documented, the physiological role of the extracellular domains remains elusive. Here we report the generation of CD45-antisense transfected Jurkat T cell clones that lack CD45 or have been reconstituted to uniquely express either the smallest, CD45(0), or the largest, CD45(ABC), isoform. These cells exhibited marked isoform-dependent differences in IL-2 production and tyrosine phosphorylation of cellular proteins, including Vav after anti-CD3 stimulation. These results demonstrate that the distinct CD45 extracellular domains differentially regulate T cell receptor-mediated signaling pathways. Furthermore, these findings suggest that alterations in CD45 isoform expression by individual T cells during thymic ontogeny and after antigen exposure in the periphery directly affects the signaling pathways utilized. Activation of resting T lymphocytes through the T cell receptor (TCR)1 requires expression of the CD45 family of transmembrane protein-tyrosine phosphatases (PTPases) (1, 2). CD45 has been shown to regulate the basal activity of the Fyn and Lck protein-tyrosine kinases (PTKs) by dephosphorylation of their respective regulatory carboxyl-terminal tyrosine residues (3-7). However, it is not clear that these are CD45's sole functions. For example, new evidence suggests that CD45 can also dephosphorylate certain PTK substrates, such as the TCR chain (8) and the 32-kDa CD45-associated phosphoprotein, LPAP (9). Thus, the precise functions of the CD45 phosphatase in signal transduction are incompletely understood.While the requirement for the intracellular PTPase domains has been documented (10 -13), the function of the CD45 extracellular domain in lymphocyte signal transduction remains a major unresolved issue. In humans, five CD45 isoforms, ranging in size from 180 -220 kDa, are generated by the regulated alternative mRNA splicing of three exons, encoded by a single gene (14 -16). The alternatively spliced exons, commonly referred to as A, B, and C, are located near the 5Ј end of the gene and give rise to isoforms that differ only in their extracellular regions. Individual lymphocytes simultaneously express more than one CD45 isoform (17,18). However, the expression of certain isoforms is highly regulated, resulting in their differential expression on lymphocytes of different lineage (e.g. T versus B cells), as well as on distinct functional subsets of T cells (19 -22). Furthermore, individual T cells alter their isoform expression in ...

Background. Urinary excretion of 5‐S‐cysteinyldopa (5‐S‐CD) has been used as a biochemical marker of melanoma progression. Melanomas produce not only 5‐S‐CD but also 5,6‐dihydroxyindole‐2‐carboxylic acid (5,6DHI2C) as major intermediates in melanin formation. 5,6DHI2C is then metabolized to the two O‐methyl derivatives, 5H6MI2C and 6H5MI2C. The aim of this study was to determine which marker in serum and urine most sensitively reflected the progression of melanoma. Methods. Serum and 24‐hour urine samples were collected and assayed serially by high‐performance liquid chromatography every 1 to 4 months in 28 patients with primary or recurrent melanomas, for up to 48 months. Results. Serum concentration and urinary excretion of 5‐S‐CD and 6H5MI2C in patients with melanoma without metastases were close to those obtained from normal subjects. Metastases developed in 9 of the 28 patients. In seven of these nine patients, serum or urinary 5‐S‐CD values were elevated before or at the time of clinical detection of visceral metastases. However, serum 5‐S‐CD was elevated significantly earlier and reflected melanoma progression better than the physical examination and/or laboratory tests, such as scintigraphy and echography. Serum 6H5MI2C values exceeded the normal range shortly before death in three patients, and urinary 6H5MI2C did not increase at any stage in most patients, therefore these metabolites did not reflect progression of disease. Conclusions. Among the four markers, serum 5‐S‐CD appears to be the best biochemical marker for the detection of progression of melanotic melanoma, a value of more than 10 nmol/1 suggesting the presence of metastasis.

These results indicate that anti-CD45 mAbs are potent immunomodulatory agents, able to sustain indefinite islet allograft function after a short treatment course in the highly immunogenic model of islet transplantation.

We studied the effect of potassium iodide on the chemotaxis of neutrophil in 15 healthy subjects with a modified Boyden chamber method. Orally administered potassium iodide (15 mg/kg/day for 3 days) significantly inhibited the neutrophil chemotaxis in peripheral blood. It is postulated that the therapeutic effect of potassium iodide on erythema nodosum, nodular vasculitis, and Sweet's syndrome might be mediated through the inhibition of neutrophil chemotaxis by this agent.