LAMP1/CD107a is required for efficient perforin delivery to lytic granules and NK-cell cytotoxicity

The central role of the cytoskeleton in mechanisms and functions of the NK cell immune synapse

Natural killer (NK) cells discriminate between healthy and unhealthy target cells through a balance of activating and inhibitory signals at direct intercellular contacts called immune synapses. Rearrangements in the cellular cytoskeleton have long been known to be critical in assembly of immune synapses. Here, through bringing together the vast literature on this subject, the number of different ways in which the cytoskeleton is important becomes evident. The dynamics of filamentous actin are critical in (i) creating the nanometer-scale organization of NK cell receptors, (ii) establishing cellular polarity, (iii) coordinating immune receptor and integrin-mediated signaling, and (iv) directing secretion of lytic granules and cytokines. The microtubule network also is important in the delivery of lytic granules and vesicles containing cytokines to the immune synapse. Together, these data establish that the cytoskeleton acts as a central regulator of this complex and dynamic process - and an enormous amount of NK cell biology is controlled through the cytoskeleton.

Effects of cryopreservation on effector cells for antibody dependent cell-mediated cytotoxicity (ADCC) and natural killer (NK) cell activity in (51)Cr-release and CD107a assays

Freshly isolated PBMC are broadly used as effector cells in functional assays that evaluate antibody-dependent cell mediated cytotoxicity (ADCC) and NK activity; however, they introduce natural-individual donor-to-donor variability. Cryopreserved PBMC provide a more consistent source of effectors than fresh cells in cytotoxicity assays. Our objective was to determine the effects of cryopreservation of effector PBMC on cell frequency, and on the magnitude and specificity of ADCC and NK activity. Fresh, frozen/overnight rested and frozen/not rested PBMC were used as effector cells in (51)Cr-release and CD107a degranulation assays. Frozen/overnight rested PBMC had higher ADCC and NK activity in both assays when compared to fresh PBMC; however, when using frozen/not rested PBMC, ADCC and NK activities were significantly lower than fresh PBMC. Background CD107a degranulation in the absence of target cell stimulation was greater in PBMC that were frozen/not rested when compared to fresh PBMC or PBMC that were frozen overnight and rested. The percentages of CD16(+)CD56(dim) NK cells and CD14(+) monocytes were lower in PBMC that were frozen and rested overnight than in fresh PBMC. CD16 expression on CD56(dim) NK cells was similar for all PBMC treatments. PBMC that were frozen and rested overnight were comparable to fresh PBMC effectors. PBMC that were frozen and used immediately when evaluating ADCC or NK activity using either a (51)Cr-release assay or a CD107a degranulation assay had the lowest activity. Clinical studies of antibodies that mediate ADCC would benefit from using effector cells that have been frozen, thawed and rested overnight prior to assay.

Cell biological steps and checkpoints in accessing NK cell cytotoxicity

Natural killer (NK) cell-mediated cytotoxicity is governed by the formation of a lytic immune synapse in discrete regulated steps, which give rise to an extensive array of cellular checkpoints in accessing NK cell-mediated cytolytic defense. Appropriate progression through these cell biological steps is critical for the directed secretion of specialized secretory lysosomes and subsequent target cell death. Here we highlight recent discoveries in the formation of the NK cell cytolytic synapse as well as the molecular steps and cell biological checkpoints required for this essential host defense process.

Hemophagocytic syndrome in children and adults

Hemophagocytic syndrome, also known as hemophagocytic lymphohistiocytosis (HLH), is a heterogenic syndrome, which leads to an acute, life-threatening inflammatory reaction. HLH occurs both in children and adults, and can be triggered by various inherited as well as acquired factors. Depending on the etiology, HLH can be divided into genetic (i.e., primary) and acquired (i.e., secondary) forms. Among genetic HLH forms, one can distinguish between familial HLH and other genetically conditioned forms of HLH. Acquired HLH can be typically triggered by infections, autoimmune diseases, and malignancies. The most common symptoms of HLH are unremitting fever, splenomegaly, and peripheral blood cytopenia. Some severely ill patients present with central nervous system involvement. Laboratory tests reveal hyperferritinemia (often >10,000 μg/L), increased serum concentration of soluble receptor α for interleukin-2 (>2,400 U/L), hypertriglyceridemia, hypofibrinogenemia, coagulopathy, hyponatremia, hypoproteinemia, and elevated liver transaminases and bilirubin. Prognosis in HLH is very serious. Genetic HLH is always lethal if adequate therapy is not administered. Similarly, severe acquired cases often lead to death without appropriate treatment. Since HLH can be encountered by various specialists in the medical field, basic knowledge of this entity such as diagnostic criteria and treatment should be familiar to all physicians.

Gap junction intercellular communications regulate NK cell activation and modulate NK cytotoxic capacity

Gap junctions (GJs) mediate intercellular communication between adjacent cells. Previously, we showed that connexin 43 (Cx43), the main GJ protein in the immune system, mediates Ag transfer between human dendritic cells (DCs) and is recruited to the immunological synapse during T cell priming. This crosstalk contributed to T cell activation, intracellular Ca(2+) responses, and cytokine release. However, the role of GJs in NK cell activation by DCs and NK cell-mediated cytotoxicity against tumor cells remains unknown. In this study, we found polarization of Cx43 at the NK/DC and NK/tumor cell-contact sites, accompanied by the formation of functional GJs between NK/DCs and NK/tumor cells, respectively. Cx43-GJ-mediated intercellular communication (GJIC) between human NK and DCs was bidirectional. Blockage of Cx43-GJIC inhibited NK cell activation, though it affected neither the phenotype nor the function of DCs. Cx43 knockdown or inhibition using mimetic peptides greatly reduced CD69 and CD25 expression and IFN-γ release by DC-stimulated NK cells. Moreover, blocking Cx43 strongly inhibited the NK cell-mediated tumor cell lysis associated with inhibition of granzyme B activity and Ca(2+) influx. Our data identify a novel and active role for Cx43-GJIC in human NK cell activation and antitumor effector functions that may be important for the design of new immune therapeutic strategies.