The activating receptors 2B4 and NTB-A, but not CRACC are subject to ligand-induced down-regulation on human natural killer cells

Activation of natural killer cells can be mediated by different receptors. Stimulation of the receptors 2B4, NTB-A and CRACC, members of the SLAM-related receptor family, induces cytotoxicity and cytokine production. The surface expression of 2B4 and other activating natural killer cell receptors is down-modulated after receptor engagement, which results in a weaker response to consecutive stimulation. We tested whether this regulatory mechanism applies to all SLAM-related receptors expressed by primary human natural killer cells. After co-culture with target cells expressing the respective ligands different effects on receptor surface expression were observed. While 2B4 ex-pression was strongly reduced, NTB-A showed less prominent down-modulation and the expression level of CRACC remained unchanged. The expression levels of the receptor-proximal signaling molecules SAP, EAT-2 and FynT did not change after receptor engagement. Co-culture with target cells expressing the ligands for NTB-A or CRACC had no impact on subsequent NTB-A or CRACC-mediated NK cell activation

Regulation of human lymphocytes by SLAM-related receptors

The six members of the SLAM-related receptor family are expressed on many cell types of the immune system and play a role in fine-tuning of immune responses. In this study we investigated the SLAM-related receptors 2B4, NTB-A and CRACC. 2B4 and NTB-A are activating receptors on human natural killer (NK) cells. 2B4 binds to CD48, NTB A is homophilic. The molecular basis for the homophilic NTB A interaction has been identified by crystal structure analysis, but the results have not been tested in functional assays. Using mutational analysis we could show that the residues H54 and S90 are very important for functional homophilic interaction between two NTB A molecules, whereas the residues E37 and Q88 are not. After binding to their ligands 2B4 and NTB A recruit the two adapter molecules SAP and EAT 2. Although many elements of 2B4 and NTB A signaling have been described, the early events in their signal transduction are not fully understood. In this study we could show that in human natural killer cells the phosphorylation of 2B4 and NTB A takes place independently of SAP. However, both receptors need the presence of SAP to trigger cytotoxic responses. The adapter EAT 2 does not bind to the phosphorylated receptors in the absence of SAP. This leads to the conclusion that SAP association with the receptors is the crucial prerequisite for further signaling events, including the recruitment of EAT 2. CRACC is an activating receptor on NK cells triggering cytotoxicity and enhancing cytokine production. The receptor is also expressed on a subset of CD8-positive and few CD4-positive T cells, but the function of CRACC on these cells is unknown. In this study we describe CRACC as co-stimulatory receptor on T cells. Simultaneous engagement of the T cell receptor and CRACC induces expression of activation markers, proliferation and cytokine production. T cell-mediated cytotoxicity is not enhanced by engagement of CRACC. We found that CRACC is expressed mainly on CD8-positive memory T cells, and its expression is induced on CD8-positive T cells by activation. Therefore we suggest that CRACC co-stimulation supports the expansion of activated cells and facilitates the re-activation of memory T cells. Furthermore we could detect CRACC expression on CD4-positive, CD28-negative T cells in patients with unstable angina pectoris. This population appears in patients with chronic inflammatory diseases and amplifies the inflammatory process. We suggest that CRACC co-stimulation could be involved in the continuous activation of these cells, and therefore is a possible therapeutical target

NK cell cytotoxicity mediated by 2B4 and NTB-A is dependent on SAP acting downstream of receptor phosphorylation

2B4 (CD244) and NK-T-B-antigen (NTB-A, CD352) are activating receptors on human natural killer (NK) cells and belong to the family of signaling lymphocyte activation molecule (SLAM)-related receptors (SRR). Engagement of these receptors leads to phosphorylation of their cytoplasmic tails and recruitment of the adapter proteins SLAM-associated protein (SAP) and Ewing's sarcoma-activated transcript-2 (EAT-2). X-linked lymphoproliferative syndrome (XLP) is a severe immunodeficiency that results from mutations in the SAP gene. 2B4 and NTB-A-mediated cytotoxicity are abrogated in XLP NK cells. To elucidate the molecular basis for this defect we analyzed early signaling events in SAP knockdown cells. Similar to XLP NK cells, knockdown of SAP in primary human NK cells leads to a reduction of 2B4 and NTB-A-mediated cytotoxicity. We found that early signaling events such as raft recruitment and receptor phosphorylation are not affected by the absence of SAP, indicating the defect in the absence of SAP is downstream of these events. In addition, knockdown of EAT-2 does not impair 2B4 or NTB-A-mediated cytotoxicity. Surprisingly, EAT-2 recruitment to both receptors is abrogated in the absence of SAP, revealing a novel cooperativity between these adapters

Synthesis of optimal inventory control system with discrete PID-controller via linear matrix inequalities technique

В статье предложен подход к решению задачи оптимального управления запасами в условиях неизвестного, но ограниченного внешнего спроса и наличия структурных ограничений с помощью дискретного нестационарного ПИД-регулятора в контуре обратной связи. Подход основан на использовании квадратичных функций Ляпунова, через которые осуществляется описание инвариантных эллипсоидов достижимости замкнутой системы при действии ограниченных внешних возмущений. Использование математического аппарата линейных матричных неравенств позволило сформулировать задачу синтеза как последовательность задач полуопределенного программирования, для решения которых используются специализированные пакеты на базе системы MATLAB. Рассмотрен численный пример.An approach to the solution of the optimal inventory control under "unknown but bounded" external demand and the availability of structural constraints using the discrete non-stationary linear PID controller in the feedback loop is proposed. The approach is based on the use of quadratic Lyapunov functions, through which the description of the invariant attainability ellipsoids of a close-loop system under the action of bounded perturbations is implemented. Using the Linear Matrix Inequalities allowed to formulate the synthesis problem as a sequence of semidefinite programming, for solution which is used specialized packages based on the MATLAB system. A numerical example is considered