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Apoptosis is the most common form of neutrophil death under both physiological and inflammatory conditions. However, forms of nonapoptotic neutrophil death have also been observed. In the current study, we report that human neutrophils undergo necroptosis after exposure to GM-CSF followed by the ligation of adhesion receptors such as CD44, CD11b, CD18, or CD15. Using a pharmacological approach, we demonstrate the presence of a receptor-interacting protein kinase-3 (RIPK3)-a mixed lineage kinase-like (MLKL) signaling pathway in neutrophils which, following these treatments, first activates p38 MAPK and PI3K, that finally leads to the production of high levels of reactive oxygen species (ROS). All these steps are required for necroptosis to occur. Moreover, we show that MLKL undergoes phosphorylation in neutrophils in vivo under inflammatory conditions. This newly identified necrosis pathway in neutrophils would imply that targeting adhesion molecules could be beneficial for preventing exacerbation of disease in the neutrophilic inflammatory response., (Copyright © 2016 by The American Association of Immunologists, Inc.)

Resting human NK cells require a two-stage activation process that we have previously described as "priming" and "triggering." NK-sensitive tumor cells provide both priming and triggering signals. NK-resistant tumors evade lysis, mostly by failure to prime; however, we recently reported a tumor cell line (CTV-1) that primes resting NK cells but fails to trigger lysis. In this article, we report two additional leukemia cell lines that prime NK cells but are resistant to lysis. Tumor-mediated NK priming is via CD2 binding to a ligand within CD15 on the tumor cell. NK-resistant RAJI cells became susceptible to NK lysis following transfection and expression of CD15. Blockade of CD15 on K562 cells or on CD15(+) RAJI cells significantly inhibited lysis, as did blockade of CD2 on resting NK cells. NK priming via CD2 induced CD16 shedding, releasing CD3ζ to the CD2, leading to its phosphorylation and the subsequent phosphorylation of linker for activation of T cells and STAT-5 and synthesis of IFN-γ. Blockade of C-type lectin receptors significantly suppressed the tumor-mediated priming of NK cells, whereas blockade of Ig-superfamily-like receptors had no effect at the NK-priming stage. Tumor priming of resting NK cells was irrespective of HLA expression, and blockade of HLA-killer Ig-like receptor interactions did not influence the incidence or degree of priming. However, CD15-CD2 interactions were critical for NK priming and were required, even in the absence of HLA-mediated NK inhibition. Tumor-mediated priming led to a sustained primed state, and the activated NK cells retained the ability to lyse NK-resistant tumors, even after cryopreservation.

Daclizumab (Dac), an Ab against the IL-2R alpha-chain, inhibits brain inflammation in patients with multiple sclerosis, while expanding CD56(bright) immunoregulatory NK cells in vivo. We hypothesized that this unexpected expansion is paradoxically IL-2 driven; caused by the increased availability of T cell-derived IL-2 for NK cell signaling. To this end, we performed ex vivo functional analyses of CD56(bright) NK cells and T cells from patients in clinical trials with Dac. We developed in vitro models to investigate mechanisms for ex vivo observations. We observed that Dac treatment caused decreased numbers and proliferation of FoxP3(+) T regulatory cells (Tregs), a model T cell population known to be dependent on IL-2 for proliferation and survival. As anticipated, Dac therapy inhibited IL-2 signaling in all T cells; however, we also observed functional adaptation of T cells to low IL-2 signal in vivo, characterized by the concomitant enhancement of IL-7 signaling on all T cells and parallel increase of CD127 expression by Tregs. In contrast, IL-2 signaling on CD56(bright) NK cells was not inhibited by Dac and their in vivo proliferation and cytotoxicity actually increased. Mechanistic studies indicated that the activation of CD56(bright) NK cells was likely IL-2 driven, as low doses of IL-2, but not IL-15, mimicked this activation in vitro. Our study provides insight into the role that IL-2 and CD25 play in functional regulation of two important immunoregulatory cell populations in humans: FoxP3(+) Tregs and CD56(bright) NK cells.

C1 inhibitor (C1INH), a member of the serine proteinase inhibitor (serpin) family, is an inhibitor of proteases in the complement system, the contact system of kinin generation, and the intrinsic coagulation pathway. It is the most heavily glycosylated plasma protein, containing 13 definitively identified glycosylation sites as well as an additional 7 potential glycosylation sites. C1INH consists of two distinct domains: a serpin domain and an amino-terminal domain. The serpin domain retains all the protease-inhibitory function, while the amino-terminal domain bears most of the glycosylation sites. The present studies test the hypothesis that plasma C1INH bears sialyl Lewis(x)-related moieties and therefore binds to selectin adhesion molecules. We demonstrated that plasma C1INH does express sialyl Lewis(x)-related moieties on its N-glycan as detected using mAb HECA-452 and CSLEX1. The data also show that plasma C1INH can bind to P- and E-selectins by FACS and immunoprecipitation experiments. In a tissue culture model of endothelial-leukocyte adhesion, C1INH showed inhibition in a dose-dependent manner. Significant inhibition (>50%) was achieved at a concentration of 250 micro g/ml or higher. This discovery may suggest that C1INH plays a role in the endothelial-leukocyte interaction during inflammation. It may also provide another example of the multifaceted anti-inflammatory effects of C1INH in various animal models and human diseases.

We recently identified several individuals carrying a missense mutation (G329A; Arg(110)-Gln) in the FUT7 gene encoding fucosyltransferase VII. This enzyme is involved in the biosynthesis of the sialyl Lewis x (Le(x)) epitope on human leukocytes, which has been identified as an important component of leukocyte ligands for E- and P-selectin. No enzyme activity was measurable in expression studies in COS-7 cells using the mutated FUT7 construct. One of the identified individuals carried this mutation homozygously. Flow cytometry analysis of polymorphonuclear leukocytes (PMN) from this individual showed a nearly complete absence of staining with mAbs directed against sialyl Le(x) and a diminished staining with an E-selectin IgG chimera. However, staining with P-selectin IgG chimera and Abs directed against P-selectin glycoprotein ligand-1 was not affected by the mutation. PMN from the homozygously mutated individual was further analyzed in an in vitro flow chamber assay. The number of rolling PMN and the rolling velocities on both E- and P-selectin were in the range of PMN from nonmutated individuals. FUT4 and FUT7 mRNA was quantified in PMN isolated from individuals carrying the FUT7 mutation. It was found that PMN from both FUT7 homozygously and heterozygously mutated individuals exhibited an elevated expression of FUT4 mRNA compared with PMN from FUT7 nonmutated individuals. The elevated expression of fucosyltransferase IV was reflected as an increased expression of the Le(x) and CD65s Ags on PMN from these individuals. The significance of the mutation was supported by transfection of BJAB cells.

The T cell and NK cell adhesion molecule CD2 interacts with different ligands, viz, CD58, CD48, and CD59. Using a fluorescent multimeric construct of rCD2, we previously identified an additional CD2 ligand (CD2L) on the erythroleukemic cell line K562. CD2L bound to a different region of CD2 than known ligands and was N-glycosylation dependent. In this study we show that mAbs specific for the carbohydrate Ag Lewis x (CD15, Gal-beta 1-4 GlcNAc alpha 1-3Fuc) inhibit multimeric rCD2 binding to CD2L. CD2L is restricted in expression to myeloid cells, where it is co-expressed with CD58 on monocytes and is the dominant, if not sole, CD2 ligand on neutrophils. Sugar specificity studies show that CD2L is not CD15. Thus, whereas soluble Lewis x inhibits binding of CD15 mAb to K562 and neutrophils, binding of multimeric rCD2 is unaffected. Furthermore, multimeric rCD2 binding to K562 is inhibited by L-fucose and following treatment of K562 with an alpha 1-6 fucosidase, whereas these treatments do not inhibit the binding of CD15 mAb. Thus, it is likely that CD2L is a carbohydrate structure closely associated with, yet distinct from, CD15, which can be sterically blocked by CD15 mAb. Functional studies revealed that CD2L is probably an important CD2 ligand in the non-MHC-restricted NK cell killing of K562 target cells, since this activity was strongly inhibited by CD15 mAb. Collectively, this study indicates that a CD15 (Lewis x)-associated carbohydrate structure(s), which has previously been shown to be a selectin ligand, also may function as an important CD2 ligand on myeloid cells.

Activated monocytes express tissue factor (TF), a protein that is important in the pathogenesis of thrombotic disorders. We sought to characterize an adhesion-dependent pathway for monocyte activation. In this study, we showed that adhesion of monocytes to cytokine-activated endothelial cells (EC) increased (approximately 5- to 10-fold) monocyte procoagulant activity (PCA). The PCA was attributed to TF because it was dependent on the coagulation factors VII and X, but not VIII, and was completely blocked by an anti-TF mAb. Direct cell-cell contact between monocytes and EC was required. The induction of TF was rapid, peaked at 30 min, and persisted for 4 h. Northern analysis revealed a rapid (approximately 30 min) increase in TF mRNA following adhesion, distinct from that induced by LPS (approximately 2-4 h). Four-hour TNF-treated EC supported TF expression, but 0.5- and 24-h TNF-treated EC had no effect. An anti-E-selectin mAb (H18/7) exerted partial inhibition, whereas anti-VCAM-1, ICAM-1, and CD11/CD18 mAbs had no inhibition. Synthetic Lewis X (Le(x)) oligosaccharide partially blocked TF induction, whereas sialyl-Le(x) (sLex) oligosaccharide had no effect. Cross-linking Le(x) on monocytes, but not sLex, significantly increased (approximately 10-fold) the TF expression. Le(x) cross-linking induced TF in 30 min and lasted for 4 h. All seventeen anti-Le(x) mAbs induced significant amount of TF generation, and epitope mapping revealed a single binding epitope on Le(x). These findings indicate that adhesion of monocytes to activated EC induces TF generation, and also suggest that Le(x) may represent an important signaling molecule on monocytes.

The selectin family of cell adhesion molecules consists of three members, E-selectin (ELAM-1), L-selectin (LECAM-1), and P-selectin (CD62, GMP140, or PADGEM), which are all involved in binding of leukocytes to endothelial cells. All members have structural similarities and they can all bind to a common carbohydrate epitope, sialyl Lewis X in in vitro assays. To study cross-reactivity of the selectins in more detail we used Ig chimeras of murine and human L- and human E-selectin. All three chimeras bound to the natural ligands of L-selectin on specialized high endothelial venules in both human and murine lymphoid organs as determined by immunohistochemistry and were able to precipitate 50- and 90-kDa sulfated ligands from organ cultures of murine peripheral and mesenteric lymph nodes. This recognition was calcium dependent and inhibitable by mAb specific for the lectin domain of the respective selectin. L- and E-selectin binding to high endothelial venules and to the sulfated ligands was inhibitable by the carbohydrates, fucoidan and sialyl Lewis X, respectively. Although immunoprecipitations showed that both murine and human L-selectin could recognize the sulfated ligands from high endothelial venules more efficiently than human E-selectin at the concentrations used, both L- and E-selectin chimeras could inhibit in vivo lymphocyte trafficking into peripheral lymph nodes equally well.

Many monoclonal antibodies that react with the lacto-N-fucopentaose III (LNF III) antigenic determinant, Gal beta 1-4(Fuc alpha 1-3)GlcNAc beta 1-3Gal beta 1-4Glc, have been described recently. The terminal trisaccharide of this determinant, fucosyllactosamine, is present on glycolipids and glycoproteins and on the surface of granulocytes, monocytes, and other cells. To study the structural and genetic diversity of these antibodies, syngeneic anti-idiotypic monoclonal antibodies were produced in BALB/c mice against PMN 6, a monoclonal antibody directed against this sequence. Anti-idiotypic antibodies 6B1 and 6C4 reacted with 50% of a panel of 20 anti-LNF III monoclonal antibodies, whereas 6A3 reacted strongly only with PMN 6. This indicates that the determinants recognized by 6C4 and 6B1 represent major cross-reactive idiotopes of this family of antibodies. The binding of idiotypic antibodies to a glycolipid bearing this antigenic determinant was completely inhibited by the three anti-idiotypic antibodies, 6A3, 6B1, and 6C4. The idiotopes could be demonstrated on the heavy chain of the monoclonal antibodies by an antibody transfer technique when mild reducing conditions were employed, but a high concentration of reducing agent destroyed the idiotypic determinants. This suggests that the anti-idiotypic antibodies recognize conformational structures expressed on the heavy chain molecules. The binding of 18 monoclonal antibodies to two glycolipid antigens and to a fucosyllactosamine-bovine serum albumin conjugate was compared. Antibodies that possessed the 6C4 cross-reactive idiotope bound to fucosyllactosamine-bovine serum albumin more weakly than idiotype-negative antibodies (p = 0.001). This suggests that the 6C4-positive antibodies might represent germline structures.