Human Antibodies against Herpes Simplex Virus 2 Glycoprotein G Do Not Neutralize but Mediate Antibody-Dependent Cellular Cytotoxicity.

Herpes simplex virus 2 (HSV-2) is a sexually transmitted infection affecting 491 million individuals globally. Consequently, there is a great need for both prophylactic and therapeutic vaccines. Unfortunately, several vaccine clinical trials, primarily employing the glycoprotein D of HSV-2 (gD-2), have failed. The immune protection conferred by human anti-HSV-2 antibodies in genital infection and disease remains elusive. It is well-known that gD-2 elicits cross-reactive neutralizing antibodies, i.e., anti-gD-2 antibodies recognize gD in HSV-1 (gD-1). In contrast, anti-glycoprotein G in HSV-2 (mgG-2) antibodies are exclusively type-specific for HSV-2. In this study, truncated versions of gD-2 and mgG-2 were recombinantly produced in mammalian cells and used for the purification of anti-gD-2 and anti-mgG-2 antibodies from the serum of five HSV-2-infected subjects, creating a pool of purified antibodies. These antibody pools were utilized as standards together with purified mgG-2 and gD-2 antigens in ELISA to quantitatively estimate and compare the levels of cross-reactive anti-gD-1 and anti-gD-2 antibodies, as well as anti-mgG-2 antibodies in sera from HSV-1+2-, HSV-2-, and HSV-1-infected subjects. The median concentration of anti-mgG-2 antibodies was five times lower in HSV-1+2-infected subjects as compared with cross-reactive anti-gD-1 and anti-gD-2 antibodies, and three times lower in HSV-2 infected subjects as compared with anti-gD-2 antibodies. The pool of purified anti-gD-2 antibodies presented neutralization activity at low concentrations, while the pool of purified anti-mgG-2 antibodies did not. Instead, these anti-mgG-2 antibodies mediated antibody-dependent cellular cytotoxicity (ADCC) by human granulocytes, monocytes, and NK-cells, but displayed no complement-dependent cytotoxicity. These findings indicate that antibodies to mgG-2 in HSV-2-infected subjects are present at low concentrations but mediate the killing of infected cells via ADCC rather than by neutralizing free viral particles. We, and others, speculate that Fc-receptor mediated antibody functions such as ADCC following HSV-2 vaccination may serve as a better marker of protection correlate instead of neutralizing activity. In an mgG-2 therapeutic vaccine, our findings of low levels of anti-mgG-2 antibodies in HSV-2-infected subjects may suggest an opportunity to enhance the immune responses against mgG-2. In a prophylactic HSV-2 mgG-2 vaccine, a possible interference in cross-reactive immune responses in already infected HSV-1 subjects can be circumvented.

Rheumatoid arthritis chondrocytes produce increased levels of pro-inflammatory proteins.

Objective: To investigate whether articular chondrocytes from rheumatoid arthritis (RA) patients have acquired a proinflammatory phenotype. Method: Articular cartilage explants from RA patients and healthy controls (HC) were cultured with or without interleukin (IL)-1ß for two weeks. Protein levels of cytokines and metalloproteinases (MMPs) in the supernatant were measured by LUMINEX, mRNA with qPCR and nitrogen oxide (NO) levels with Griess assay. Results: Within 24 â€‹h after culture, cartilage explants from RA spontaneously produced MMP-1 and MMP-13, and matrix components (aggrecan and collagen type IV) were released. In addition, the RA explants released higher levels of tumor necrosis factor, interferon-γ, IL-33, IL-18, vascular endothelial growth factor-A, IL-6 but not IL-8, and granulocyte-macrophage colony-stimulating factor (GM-CSF) as compared with HC. During two weeks of incubation the higher levels did not diminish. IL-1ß stimulation further increased the levels of IL-6, IL-8 and GM-CSF, mainly in RA explants, and induced increased levels of NO in the supernatant from both HC and RA explants, as a result of chondrocyte activation. Conclusions: RA chondrocytes are activated with a proinflammatory profile involving the production of cytokines as well as MMP-1 and MMP-13, that can lead to release of matrix molecules after activation, which suggests that the chondrocytes have a proinflammatory phenotype and thereby an active role in the pathogenesis.

Human CD38 regulates B cell antigen receptor dynamic organization in normal and malignant B cells.

CD38 is a multifunctional protein expressed on the surface of B cells in healthy individuals but also in B cell malignancies. Previous studies have suggested a connection between CD38 and components of the IgM class B cell antigen receptor (IgM-BCR) and its coreceptor complex. Here, we provide evidence that CD38 is closely associated with CD19 in resting B cells and with the IgM-BCR upon engagement. We show that targeting CD38 with an antibody, or removing this molecule with CRISPR/Cas9, inhibits the association of CD19 with the IgM-BCR, impairing BCR signaling in normal and malignant B cells. Together, our data suggest that CD38 is a new member of the BCR coreceptor complex, where it exerts a modulatory effect on B cell activation upon antigen recognition by regulating CD19. Our study also reveals a new mechanism where α-CD38 antibodies could be a valuable option in therapeutic approaches to B cell malignancies driven by aberrant BCR signaling.

Data describing expression of formyl peptide receptor 2 in human articular chondrocytes.

The formyl peptide receptor 2 (FPR2) belongs to the family of seven-transmembrane G protein-coupled receptors (GPCR) and are expressed by many different cells but mainly studied in immune cells. FPR2 is involved in host defense against bacterial infections and clearance of damaged cells through the oxidative burst and chemotaxis of neutrophils. In addition, FPR2 has also been implicated as an immunomodulator in sterile inflammations, e.g. inflammatory joint diseases. Here we present data regarding FPR2 expression in human articular chondrocytes, isolated from healthy individuals and osteoarthritic patients, on both mRNA and protein level using qPCR and Imagestream flow cytometry. We also present data after receptor stimulation and monitoring of production of nitric oxide, reactive oxygen species, IL-6, IL-8 and MMP-3. The presented data show that human articular chondrocytes from patients with osteoarthritis as well as from healthy individuals express FPR2 both at mRNA and protein level. The biological relevance of FPR2 expression in chondrocytes needs to be further investigated.

Moderate- to high intensity aerobic and resistance exercise reduces peripheral blood regulatory cell populations in older adults with rheumatoid arthritis.

OBJECTIVE: Exercise can improve immune health and is beneficial for physical function in patients with rheumatoid arthritis (RA), but the immunological mechanisms are largely unknown. We evaluated the effect of moderate- to high intensity exercise with person-centred guidance on cells of the immune system, with focus on regulatory cell populations, in older adults with RA. METHODS: Older adults (≥65 years) with RA were randomized to either 20-weeks of moderate - to high intensity aerobic and resistance exercise (n = 24) or to an active control group performing home-based exercise of light intensity (n = 25). Aerobic capacity, muscle strength, DAS28 and CRP were evaluated. Blood samples were collected at baseline and after 20 weeks. The frequency of immune cells defined as adaptive regulatory populations, CD4 + Foxp3 + CD25 + CD127- T regulatory cells (Tregs) and CD19 + CD24hiCD38hi B regulatory cells (Bregs) as well as HLA-DR-/lowCD33 + CD11b + myeloid derived suppressor cells (MDSCs), were assessed using flow cytometry. RESULTS: After 20 weeks of moderate- to high intensity exercise, aerobic capacity and muscle strength were significantly improved but there were no significant changes in Disease Activity Score 28 (DAS28) or CRP. The frequency of Tregs and Bregs decreased significantly in the intervention group, but not in the active control group. The exercise intervention had no effect on MDSCs. The reduction in regulatory T cells in the intervention group was most pronounced in the female patients. CONCLUSION: Moderate- to high intensity exercise in older adults with RA led to a decreased proportion of Tregs and Bregs, but that was not associated with increased disease activity or increased inflammation. TRIAL REGISTRATION: Improved Ability to Cope With Everyday Life Through a Person-centered Training Program in Elderly Patients With Rheumatoid Arthritis - PEP-walk Study, NCT02397798. Registered at ClinicalTrials.gov March 19, 2015.

Moderate-to-high intensity exercise with person-centered guidance influences fatigue in older adults with rheumatoid arthritis.

Fatigue is described as a dominant and disturbing symptom of rheumatoid arthritis (RA) regardless of the advances in pharmacological treatment. Fatigue is also found to correlate with depression. The objective was to evaluate the impact of moderate-to-high intensity, aerobic and resistance exercise with person-centered guidance on fatigue, anxiety and depression, in older adults with RA. Comparisons were made between older adults (> 65 years) with RA taking part in a 20-week moderate-to-high intensity exercise at a gym (n = 36) or in home-based exercise of light intensity (n = 38). Assessments were performed at baseline, at 20 weeks, and at 52 weeks. Outcomes were differences in Multidimensional Fatigue Inventory (MFI-20), Visual Analog Scale Fatigue (VAS fatigue), and Hospital Anxiety and Depression Scale (HADS). Analysis of metabolomics was also performed. The subscales "physical fatigue" and "mental fatigue" in MFI-20 and symptoms of depression using HADS depression scale improved significantly at week 20 in the exercise group compared with the control group. Exercise did not influence global fatigue rated by VAS or subscales "reduced motivation", "reduced activity" and "general fatigue" in MFI-20. No significant change was found on the anxiety index of HADS. The improvements in physical fatigue were associated with changes in the metabolism of lipids, bile acids, the urea cycle and several sugars. Moderate-to-high intensity exercise with person-centered guidance decreased fatigue and improved symptoms of depression and were accompanied by metabolic changes in older adults with RA.

CD21-/low B cells associate with joint damage in rheumatoid arthritis patients.

Depletion of B cells is beneficial in rheumatoid arthritis (RA) patients with autoantibodies to citrullinated proteins (ACPA) and/or the Fc portion of immunoglobulins (rheumatoid factor [RF]), suggesting a role for B cells in disease pathogenesis. To date, however, the identity of specifically pathogenic B cell subsets has not been discovered. One candidate population is identified by the low expression or absence of complement receptor 2 (CD21-/low B cells). In this study, we sought to determine whether there was any correlation between CD21-/low B cells and clinical outcome in patients with established RA, either ACPA+ /RF+ (n = 27) or ACPA- /RF- (n = 10). Healthy donors (n = 17) were included as controls. The proportion of the CD21-/low CD27- IgD- memory B cell subset in peripheral blood (PB) was significantly increased in ACPA+ /RF+ RA patients compared with healthy donors, and the frequency of this subset correlated with joint destruction (r = 0.57, P < 0.04). The levels of the chemokines CXCL-9 and CXCL-10 were higher in synovial fluid than in plasma, and PB CD21-/low cells expressed the receptor, CXCR3. In synovial fluid, most of the B cells were CD21-/low , approximately 40% of that population was CD27- IgD- , and a third of those expressed the pro-osteoclastogenic factor receptor activator of the nuclear factor κB ligand (RANKL). This subset also secreted RANKL, in addition to other factors such as IL-6, even in the absence of stimulation. We interpret these data as reason to propose the hypothesis that the CD27- IgD- subset of CD21-/low B cells may mediate joint destruction in patients with ACPA+ /RF+ RA.

Data on the NADPH-oxidase activity induced by WKYMVm and galectin-3 in bone marrow derived and exudated neutrophils isolated from four different mouse strains.

Neutrophils are the key players in inflammatory reactions and the release of superoxide through the NADPH-oxidase upon neutrophil activation contributes to bacterial clearance and surrounding tissue damage. Here we describe data on the mouse neutrophil NADPH-oxidase activation induced by the mouse formyl peptide receptor (Fpr) agonist WKYMVm and galectin-3. Neutrophils isolated from bone marrow, peritoneal exudated, and in vitro TNFα primed bone marrow neutrophils from four different laboratory strains (C57BL/6, DBA/1, BALB/c and NMRI) were used. Both Fpr agonist and galectin-3 activated neutrophils to release superoxide. No differences were observed in the amounts of superoxide released from neutrophils derived from four different strains.

Vaccination with the Secreted Glycoprotein G of Herpes Simplex Virus 2 Induces Protective Immunity after Genital Infection.

Herpes simplex virus 2 (HSV-2) infects the genital mucosa and establishes a life-long infection in sensory ganglia. After primary infection HSV-2 may reactivate causing recurrent genital ulcerations. HSV-2 infection is prevalent, and globally more than 400 million individuals are infected. As clinical trials have failed to show protection against HSV-2 infection, new vaccine candidates are warranted. The secreted glycoprotein G (sgG-2) of HSV-2 was evaluated as a prophylactic vaccine in mice using two different immunization and adjuvant protocols. The protocol with three intramuscular immunizations combining sgG-2 with cytosine-phosphate-guanine dinucleotide (CpG) motifs and alum induced almost complete protection from genital and systemic disease after intra-vaginal challenge with HSV-2. Robust immunoglobulin G (IgG) antibody titers were detected with no neutralization activity. Purified splenic CD4+ T cells proliferated and produced interferon-γ (IFN-γ) when re-stimulated with the antigen in vitro. sgG-2 + adjuvant intra-muscularly immunized mice showed a significant reduction of infectious HSV-2 and increased IFN-γ levels in vaginal washes. The HSV-2 DNA copy numbers were significantly reduced in dorsal root ganglia, spinal cord, and in serum at day six or day 21 post challenge. We show that a sgG-2 based vaccine is highly effective and can be considered as a novel candidate in the development of a prophylactic vaccine against HSV-2 infection.

Novel rat models to study primary genital herpes simplex virus-2 infection.

In this study we describe that six rat models (SD, WIST, LEW, BN, F344 and DA) are susceptible to intravaginal herpes simplex virus-2 (HSV-2) infection after pre-treatment with progesterone. At a virus dose of 5 × 10(6) PFU of HSV-2, all rat models were infected presenting anti-HSV-2 antibodies, infectious virus in vaginal washes, and HSV-2 DNA genome copies in lumbosacral dorsal root ganglia and the spinal cord. Most of the LEW, BN, F344, and DA rats succumbed in systemic progressive symptoms at day 8-14 post infection, but presented no or mild genital inflammation while SD and WIST rats were mostly infected asymptomatically. Infected SD rats did not reactivate HSV-2 spontaneously or after cortisone treatment. In an HSV-2 virus dose reduction study, F344 rats were shown to be most susceptible. We also investigated whether an attenuated HSV-1 strain (KOS321) given intravaginally, could protect from a subsequent HSV-2 infection. All LEW, BN, and F344 rats survived a primary HSV-1 infection and no neuronal infection was established. In BN and F344 rats, anti-HSV-1 antibodies were readily detected while LEW rats were seronegative. In contrast to naïve LEW, BN, and F344 rats where only 3 of 18 animals survived 5 × 10(6) PFU of HSV-2, 23 of 25 previously HSV-1 infected rats survived a challenge with HSV-2. The described models provide a new approach to investigate protective effects of anti-viral microbicides and vaccine candidates, as well as to study asymptomatic primary genital HSV-2 infection.

A novel receptor cross-talk between the ATP receptor P2Y2 and formyl peptide receptors reactivates desensitized neutrophils to produce superoxide.

Neutrophils express several G-protein coupled receptors (GPCRs) and they cross regulate each other. We described a novel cross-talk mechanism in neutrophils, by which signals generated by the receptor for ATP (P2Y2) reactivate desensitized formyl peptide receptors (FPRs) so that these ligand-bound inactive FPRs resume signaling. At the signaling level, the cross-talk was unidirectional, i.e., P2Y2 ligation reactivated FPR, but not vice versa and was sensitive to the phosphatase inhibitor calyculinA. Further, we show that the cross talk between P2Y2 and FPR bypassed cytosolic Ca(2+) transients and did not rely on the actin cytoskeleton. In summary, our data demonstrate a novel cross-talk mechanism that results in reactivation of desensitized FPRs and, an amplification of the neutrophil response to ATP.

The subcellular localization of the receptor for platelet-activating factor in neutrophils affects signaling and activation characteristics.

The localization in neutrophils, of the receptor for platelet-activating factor (PAFR), has been determined using subcellular fractionation and a receptor mobilization protocol. We show that the PAFR is expressed primarily in the plasma membrane. Although activation of neutrophils by PAF induces responses typical also of agonists that bind the formyl peptide receptors (FPR), known to be stored in mobilizable organelles, some quantitative as well as qualitative differences were observed when neutrophils were activated through these receptors. PAF is equipotent to fMLF (high affinity agonist for FPR1) to cleave off L-selectin and to induce granule/vesicle secretion but is more potent than fMLF to induce a rise in intracellular Ca(2+). Similar to fMLF, PAF induced also a robust release of reactive oxygen species, but with higher EC50 value and was less sensitive to a PI3K inhibitor compared to the fMLF response. Despite the lack of a granule localized storage pool of receptors, the PAF-induced superoxide production could be primed; receptor mobilization was, thus, not required for priming of the PAF response. The desensitized PAFR could not be reactivated, suggesting that distinct signaling pathways are utilized for termination of the responses triggered through FPR1 and PAFR.

Reactivation of desensitized formyl peptide receptors by platelet activating factor: a novel receptor cross talk mechanism regulating neutrophil superoxide anion production.

Neutrophils express different chemoattractant receptors of importance for guiding the cells from the blood stream to sites of inflammation. These receptors communicate with one another, a cross talk manifested as hierarchical, heterologous receptor desensitization. We describe a new receptor cross talk mechanism, by which desensitized formyl peptide receptors (FPRdes) can be reactivated. FPR desensitization is induced through binding of specific FPR agonists and is reached after a short period of active signaling. The mechanism that transfers the receptor to a non-signaling desensitized state is not known, and a signaling pathway has so far not been described, that transfers FPRdes back to an active signaling state. The reactivation signal was generated by PAF stimulation of its receptor (PAFR) and the cross talk was uni-directional. LatrunculinA, an inhibitor of actin polymerization, induced a similar reactivation of FPRdes as PAF while the phosphatase inhibitor CalyculinA inhibited reactivation, suggesting a role for the actin cytoskeleton in receptor desensitization and reactivation. The activated PAFR could, however, reactivate FPRdes also when the cytoskeleton was disrupted prior to activation. The receptor cross talk model presented prophesies that the contact on the inner leaflet of the plasma membrane that blocks signaling between the G-protein and the FPR is not a point of no return; the receptor cross-talk from the PAFRs to the FPRdes initiates an actin-independent signaling pathway that turns desensitized receptors back to a signaling state. This represents a novel mechanism for amplification of neutrophil production of reactive oxygen species.

Galectin 3 aggravates joint inflammation and destruction in antigen-induced arthritis.

OBJECTIVE: Galectin 3, an endogenous ß-galactoside-binding lectin, plays an important role in the modulation of immune responses. The finding that galectin 3 is present in the inflamed synovium in patients with rheumatoid arthritis suggests that the protein is associated with the pathogenesis of this disease. We undertook this study to investigate the influence of galectin 3 deficiency in a murine model of arthritis. METHODS: Wild-type (WT) and galectin 3-deficient (galectin 3(-/-) ) mice were subjected to antigen-induced arthritis (AIA) through immunization with methylated bovine serum albumin. The concentration of serum cytokines (interleukin-6 [IL-6] and tumor necrosis factor α [TNFα]) and antigen-specific antibodies was evaluated using a cytometric bead array platform and enzyme-linked immunosorbent assay (ELISA). Cellular IL-17 responses were examined by flow cytometry, ELISA, and enzyme-linked immunospot assay. RESULTS: The joint inflammation and bone erosion of AIA were markedly suppressed in galectin 3(-/-) mice as compared with WT mice. The reduced arthritis in galectin 3(-/-) mice was accompanied by decreased levels of antigen-specific IgG and proinflammatory cytokines. The frequency of IL-17-producing cells in the spleen was reduced in galectin 3(-/-) mice as compared with WT mice. Exogenously added recombinant galectin 3 could partially restore the reduced arthritis and cytokines in galectin 3(-/-) mice. CONCLUSION: Our findings show that galectin 3 plays a pathogenic role in the development and progression of AIA and that the disease severity is accompanied by alterations of antigen-specific IgG levels, systemic levels of TNFα and IL-6, and frequency of IL-17-producing T cells. To our knowledge, this is the first report of in vivo evidence that galectin 3 plays a crucial role in the development of arthritis.

Mice chronically fed high-fat diet have increased mortality and disturbed immune response in sepsis.

BACKGROUND: Sepsis is a potentially deadly disease that often is caused by gram-positive bacteria, in particular Staphylococcus aureus (S. aureus). As there are few effective therapies for sepsis, increased basic knowledge about factors predisposing is needed. METHODOLOGY/PRINCIPAL FINDINGS: The purpose of this study was to study the effect of Western diet on mortality induced by intravenous S. aureus inoculation and the immune functions before and after bacterial inoculation. Here we show that C57Bl/6 mice on high-fat diet (HFD) for 8 weeks, like genetically obese Ob/Ob mice on low-fat diet (LFD), have increased mortality during S. aureus-induced sepsis compared with LFD-fed C57Bl/6 controls. Bacterial load in the kidneys 5-7 days after inoculation was increased 10-fold in HFD-fed compared with LFD-fed mice. At that time, HFD-fed mice had increased serum levels and fat mRNA expression of the immune suppressing cytokines interleukin-1 receptor antagonist (IL-1Ra) and IL-10 compared with LFD-fed mice. In addition, HFD-fed mice had increased serum levels of the pro-inflammatory IL-1beta. Also, HFD-fed mice with and without infection had increased levels of macrophages in fat. The proportion and function of phagocytosing granulocytes, and the production of reactive oxygen species (ROS) by peritoneal lavage cells were decreased in HFD-fed compared with LFD-fed mice. CONCLUSIONS: Our findings imply that chronic HFD disturb several innate immune functions in mice, and impairs the ability to clear S. aureus and survive sepsis.

The host defense peptide LL-37 selectively permeabilizes apoptotic leukocytes.

LL-37 is a cationic host defense peptide that is highly expressed during acute inflammation and that kills bacteria by poorly defined mechanisms, resulting in permeabilization of microbial membranes. High concentrations of LL-37 have also been reported to have cytotoxic effects against eukaryotic cells, but the peptide is clearly capable of differentiating between membranes with different compositions (eukaryotic versus bacterial membranes). Eukaryotic cells such as leukocytes change their membrane composition during apoptotic cell death, when they are turned into nonfunctional but structurally intact entities. We tested whether LL-37 exerted specific activity on apoptotic cells and found that the peptide selectively permeabilized the membranes of apoptotic human leukocytes, leaving viable cells unaffected. This activity was seemingly analogous to the direct microbicidal effect of LL-37, in that it was rapid, independent of known surface receptors and/or active cell signaling, and inhibitable by serum components such as high-density lipoprotein. A similar selective permeabilization of apoptotic cells was recorded for both NK cells and neutrophils. In the latter cell type, LL-37 permeabilized both the plasma and granule membranes, resulting in the release of both lactate dehydrogenase and myeloperoxidase. Apoptosis is a way for inflammatory cells to die silently and minimize collateral tissue damage by retaining tissue-damaging and proinflammatory substances within intact membranes. Permeabilization of apoptotic leukocytes by LL-37, accompanied by the leakage of cytoplasmic as well as intragranular molecules, may thus shift the balance between pro- and anti-inflammatory signals and in this way be of importance for the termination of acute inflammation.

Tumour necrosis factor (TNF)-alpha primes murine neutrophils when triggered via formyl peptide receptor-related sequence 2, the murine orthologue of human formyl peptide receptor-like 1, through a process involving the type I TNF receptor and subcellular granule mobilization.

Neutrophil granulocytes play an important role in innate host defence against microbial invasions and they are also the key effector cells in mediating host tissue damage. These functions often rely on the production of reactive oxygen species (ROS) from the membrane-bound NADPH-oxidase system. The magnitude of ROS production varies depending on the state of the cells, i.e. resting or primed. Many priming agents as well as potent NADPH-oxidase activators have been identified and characterized for human neutrophils. The cytokine tumour necrosis factor (TNF)-alpha is one prominent example of a priming agent and the synthetic hexapeptide WKYMVm is an agonist that triggers an activation of the NADPH-oxidase of human neutrophils through two members of the formyl peptide family of receptors, formyl peptide receptor (FPR) and FPR-like 1 (FPRL1). This peptide also activates murine neutrophils but the precise receptor involved has not been previously characterized. We show in this study that WKYMVm activates stably transfected HL60 cells expressing murine formyl peptide receptor-related sequence 2 (Fpr-rs2) and that activation of murine neutrophils with WKYMVm is blocked by an FPRL1-specific antagonist. WKYMVm is thus an agonist for Fpr-rs2 and we suggest that this receptor is in fact the mouse orthologue of FPRL1. In addition, we show that the WKYMVm response in murine neutrophils can be primed by TNF-alpha and this priming process involves mobilization of subcellular granules. The results obtained using neutrophils derived from TNF receptor type I (TNFRI)-deficient animals suggest that TNF-alpha exerts its priming effect via the TNFRI.

The beta-galactoside binding immunomodulatory lectin galectin-3 reverses the desensitized state induced in neutrophils by the chemotactic peptide f-Met-Leu-Phe: role of reactive oxygen species generated by the NADPH-oxidase and inactivation of the agonist.

Neutrophils interacting with a chemoattractant gradually become nonresponsive to further stimulation by the same agonist, a process known as desensitization. Receptor desensitization is a highly regulated process that involves different mechanisms depending on which receptor-ligand pair that is studied. Galectin-3, a member of a large family of beta-galactoside-binding lectins, has been suggested to be a regulator of the inflammatory process, augmenting or directly triggering the neutrophil functional repertoire. We show here that the desensitized state of neutrophils interacting with the chemotactic peptide fMLF is broken by galectin-3 and that this is achieved through an oxygen radical-mediated inactivation of the chemoattractant. The effect was inhibited by the competitor lactose and required the affinity of galectin-3 for N-acetyllactosamine, a saccharide typically found on cell surface glycoproteins. The latter was shown using a galectin-3 mutant that lacked N-acetyllactosamine binding activity, and this protein was not active. The mechanism behind the inactivation of the chemoattractant was found to depend on the ability of galectin-3 to induce a neutrophil generation/secretion of reactive oxygen species which in combined action with myeloperoxidase inactivated the peptides.