SUMMARY SWAP-70-like adaptor of T cells (SLAT) is a guanine nucleotide exchange factor for Rho GTPases that regulates the development of T helper 1 (Th1) and Th2 cell inflammatory responses by controlling the Ca2+-NFAT signaling pathway. However, the mechanism used by SLAT to regulate these events is unknown. Here, we report that the T cell receptor (TCR)-induced translocation of SLAT to the immunological synapse required Lck-mediated phosphorylation of two tyrosine residues located in an immunoreceptor tyrosine-based activation motif-like sequence but was independent of the SLAT PH domain. This subcellular relocalization was coupled to, and necessary for, activation of the NFAT pathway. Furthermore, membrane targeting of the SLAT Dbl-homology (catalytic) domain was sufficient to trigger TCR-mediated NFAT activation and Th1 and Th2 differentiation in a Cdc42-dependent manner. Therefore, tyrosine-phosphorylation-mediated relocalization of SLAT to the site of antigen recognition is required for SLAT to exert its pivotal role in NFAT-dependent CD4+ T cell differentiation.

Despite the clear functional importance of CD28 costimulation, the signaling pathways transduced through CD28 have remained controversial. PI3K was identified early as a candidate for CD28 signaling, but conflicting data during the past decade has left the role of PI3K unresolved. In this report, we have resolved this controversy. We show that mutation of the PI3K interaction site in the cytosolic tail of CD28 site disrupts the ability of CD28 to recruit protein kinase C-θ to the central supramolecular activation cluster (c-SMAC) region of the immunological synapse, promote NF-κB nuclear translocation, and enhance IL-2 gene transcription. In contrast, mutation of the PI3K interaction site had no effect on the ability of CD28 to enhance IL-2 mRNA stability. These results suggest that two distinct pathways mediate CD28-induced up-regulation of IL-2 expression, a PI3K-dependent pathway that may function through the immunological synapse to enhance IL-2 transcription and a PI3K-independent pathway that induces IL-2 mRNA stability.

This review will focus on the origins and function of Treg in peripheral self-tolerance. We will summarize the role of Treg in preventing autoimmune diseases, with a particular focus on Type 1 Diabetes (T1D), and discuss the prospects for Treg-based therapies for autoimmune diseases.

NF-B is a family of essential transcription factors involved in both embryonic development and inflammatory responses of the immune system. NF-B can be activated by two pathways, i.e. the canonical (NF-B1) pathway, which acts through the catalytic components of the IB kinase complex and leads to IB phosphorylation, degradation, and subsequent NF-B nuclear translocation, or the non-canonical (NF-B2) pathway, which involves NF-B-induced kinase-dependent proteolytic processing of p100/p52 to yield translocationcompetent p52-containing NF-B complexes. We examined the relative roles of the NF-B1 and NF-B2 pathways in TCR/CD28 costimulation. We found that TCR/CD28 costimulation activates the canonical but not the non-canonical NF-B pathway and that the serine/ threonine kinase protein kinase C (PKC) is essential for TCR/CD28-mediated canonical NF-B activation in T cells. Importantly, TCR/CD28 costimulation induces higher p52 protein levels in T cells, but this effect is secondary to enhanced de novo synthesis of p100, not to enhanced processing of extant p100; PKC deficiency impairs signal-dependent p52 accumulation because of defects in p100 production. Finally, we found that TCR/ CD28 costimulation induces IB␣, IB␤, and IB⑀ degradation, and PKC is required for IB␣ and IB⑀ but not IB␤ degradation. PKC acts solely within the canonical pathway to activate NF-B, and PKC deficiency impacts upon p100/p52 processing in a manner that is independent of NF-B-induced kinase. Nuclear factor B (NF-B)1 is a family of essential transcription factors with a well recognized role in regulating the T cell response to foreign antigen. The members of the NF-B protein family, p100/p52, p105/p50, p65 (RelA), RelB, and cRel, share a structural motif called a Rel homology domain that contains regions permitting protein dimerization, DNA binding, and nuclear localization. Limited proteolytic processing of the p100 and p105 proteins generates p52 and p50, respectively, and NF-B DNA binding and transactivation is carried out by heterodimers of p50 or p52 with one of the transactivation-domain containing Rel proteins (RelA, RelB, or c-Rel) (1).Activation (nuclear translocation and DNA binding) of NF-B heterodimers is stimulated by upstream signaling events that impact on proteins of the inhibitor of B (IB) kinase (IKK) complex, which consists of two catalytic components, IKK␣ (IKK1) and IKK␤ (IKK2), and the adaptor protein IKK␥ (NF-B essential modulator (NEMO)). Activated IKK␣ or IKK␤ phosphorylates proteins of the IB family, which is comprised of IB␣, IB␤, IB⑀, p100, and p105 (1). IB␣, IB␤, and IB⑀ bind to NF-B heterodimers in the cytoplasm, masking one (IB␣ and IB⑀) or both (IB␤) of the NF-B nuclear localization sequences. IB␣ and IB⑀ also contain nuclear export sequences that ensure rapid export of IB-bound NF-B molecules from the cell nucleus; therefore, when NF-B complexes are bound to IB, NF-B is predominantly localized in the cytoplasm (2, 3). Importantly, the carboxyl-terminal portions of p100 and p105 bear significant homology to other...

Following peripheral nerve transection, a series of biochemical changes occurs in axons and Schwann cells both at the site of the lesion and distal to it. Macrophages differentiated from monocytes that invade the area in response to transection (elicited macrophages) and, perhaps, also macrophages normally present in the tissue (resident macrophages) play important roles in these changes. In addition, nerve transection produces changes in the cell bodies of axotomized neurons and their surrounding glial cells, located at some distance from the lesion. To determine whether macrophages might play a role in the changes occurring in the superior cervical ganglion (SCG) after axotomy, we examined the presence of macrophages before and after axonal damage. The monoclonal antibodies ED1, ED2, and OX6 were used, each of which recognizes a somewhat different population of macrophages. Ganglia from normal rats contained a population of resident cells that were ED2+ but very few that were ED1+. Within 2 days after the post-ganglionic nerves were transected, the number of ED1+ cells increased substantially, with little change in immunostaining for ED2. These data, in combination with published studies on other tissues, suggest that ED1 in the SCG is selective for elicited macrophages and ED2 for resident macrophages. OX6 immunostaining was prominent in normal ganglia but also increased significantly after axotomy, suggesting that it reflects both macrophage populations. Systemic administration of 6-hydroxydopamine, a neurotoxin that causes the destruction of sympathetic nerve endings, also produced an increase in ED1 immunostaining. Thus, the change in ED1 immunostaining in the SCG does not require surgery, with the attendant severing of local blood vessels and connective tissue, but rather only the disconnection of sympathetic neurons from their end organs. The time course of the invasion of monocytes after axotomy indicates that this process is not required to trigger the biochemical changes occurring in the ganglion within the first 24 h. On the other hand, the existence of a resident population of macrophages raises the possibility that changes in those cells might be involved.