Defective neutrophil degranulation induced by interleukin-8 and complement 5a and down-regulation of associated receptors in children vertically infected with human immunodeficiency virus type 1

Effect of Antiretroviral Therapy on Neutrophil Oxidative Burst in Children

OBJECTIVE

To ascertain the effect of human immunodeficiency virus (HIV) infection, as well as, antiretroviral therapy (ART) on neutrophil oxidative burst in children.

METHODS

Fifty-five children living with HIV infection (30 receiving ART for ≥ 2 y, 25 treatment-naïve) and 30 healthy controls, aged 18 mo-18 y, were assessed for hemogram and neutrophil oxidative burst. The treatment-naïve children were followed up and the above tests were repeated after 6 mo of ART.

RESULTS

Mean (SD) serum MPO activity at 6 mo after ART [32.1 (± 19.9) U/L] was comparable to that at disease onset [17.2 (± 23.0) U/L], although it was significantly higher compared to that in children on ART ≥ 2 y [13.3 (± 15.8) U/L] and controls [12.1 (± 11.9) U/L]. Median fluorescence intensity (MFI) of unstimulated DHR was highest at 6 mo after ART and in the treatment-naïve group, which was significantly higher than in the controls, as well as, children receiving ART ≥ 2 y. Stimulation index was highest in the control group [442.4 (341.9-562.9)], which was comparable to that in children on ART ≥ 2 y [304.2 (153.2-664.8)], but was significantly higher than the treatment-naïve cohort [266.1 (148.2-339.4)] and children on ART for 6 mo [318.8 (154.9-395.6)].

CONCLUSION

A hyperinflammatory state caused by an increased serum myeloperoxidase enzyme activity and increased basal neutrophil oxidative burst was seen in untreated HIV infection and during initial 6 mo of ART. ART given for ≥ 2 y normalized the impaired neutrophilic phagocytic functions.

Orchestration of Neutrophil Extracellular Traps (Nets), a Unique Innate Immune Function during Chronic Obstructive Pulmonary Disease (COPD) Development

Morbidity, mortality and economic burden caused by chronic obstructive pulmonary disease (COPD) is a significant global concern. Surprisingly, COPD is already the third leading cause of death worldwide, something that WHO had not predicted to occur until 2030. It is characterized by persistent respiratory symptoms and airway limitation due to airway and/or alveolar abnormalities usually caused by significant exposure to noxious particles of gases. Neutrophil is one of the key infiltrated innate immune cells in the lung during the pathogenesis of COPD. Neutrophils during pathogenic attack or injury decide to undergo for a suicidal death by releasing decondensed chromatin entangled with antimicrobial peptides to trap and ensnare pathogens. Casting neutrophil extracellular traps (NETs) has been widely demonstrated to be an effective mechanism against invading microorganisms thus controlling overwhelming infections. However, aberrant and massive NETs formation has been reported in several pulmonary diseases, including chronic obstructive pulmonary disease. Moreover, NETs can directly induce epithelial and endothelial cell death resulting in impairing pulmonary function and accelerating the progression of the disease. Therefore, understanding the regulatory mechanism of NET formation is the need of the hour in order to use NETs for beneficial purpose and controlling their involvement in disease exacerbation. For example, DNA neutralization of NET proteins using protease inhibitors and disintegration with recombinant human DNase would be helpful in controlling excess NETs. Targeting CXC chemokine receptor 2 (CXCR2) would also reduce neutrophilic inflammation, mucus production and neutrophil-proteinase mediated tissue destruction in lung. In this review, we discuss the interplay of NETs in the development and pathophysiology of COPD and how these NETs associated therapies could be leveraged to disrupt NETopathic inflammation as observed in COPD, for better management of the disease.

Corticosteroid use and increased CXCR2 levels on leukocytes are associated with lumacaftor/ivacaftor discontinuation in cystic fibrosis patients homozygous for the F508del CFTR mutation

Cystic fibrosis (CF) is the most common life-shortening genetic disease and is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Several current therapies aim at improving availability and/or function of the mutant CFTR proteins. The combination therapeutic lumacaftor/ivacaftor (Orkambi, luma/iva) partially corrects folding and potentiates CFTR function impaired by the F508del mutation. Despite the potential for clinical benefit, a substantial number of patients discontinue treatment due to intolerable adverse effects. The aim of the present study is to identify differences between individuals who continued treatment and those who discontinued due to adverse respiratory effects to potentially inform treatment decisions. Clinical data from the year prior to treatment initiation were analyzed from 82 patients homozygous for the F508del mutation treated at the Colorado Adult CF Program. Blood samples were collected from 30 of these subjects before initiation of treatment to examine expression of circulating leukocyte surface antigens and cytokines. Clinical and demographic characteristics were analyzed along with inflammatory markers to determine biomarkers of drug discontinuation. The use of oral prednisone and/or nasal budesonide in the year prior to luma/iva initiation was more prevalent in CF subjects who did not tolerate luma/iva (82% vs. 43%). Increased age, but not gender or initial lung function, was associated with higher probability of discontinuing treatment due to side effects overall. Worse lung function (lower ppFEV₁, ppFEF_25-75 ≤ 60%) was associated with higher incidence of discontinuing treatment due to pulmonary adverse effects. In a nested cohort of patients, increased surface levels of CXCR2 on CD14+CD16- monocytes were associated with discontinuation. Overall, the patients who tolerated luma/iva were distinguishable from those who did not tolerate the drug based on clinical and cellular markers obtained prior to treatment initiation.

The role of polymorphonuclear neutrophils during HIV-1 infection

It is well-recognized that human immunodeficiency virus type-1 (HIV-1) mainly targets CD4⁺ T cells and macrophages. Nonetheless, during the past three decades, a huge number of studies have reported that HIV-1 can directly or indirectly target other cellular components of the immune system including CD8⁺ T cells, B cells, dendritic cells, natural killer cells, and polymorphonuclear neutrophils (PMNs), among others. PMNs are the most abundant leukocytes in the human circulation, and are known to play principal roles in the elimination of invading pathogens, regulating different immune responses, healing of injured tissues, and maintaining mucosal homeostasis. Until recently, little was known about the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression. This is because early studies focused on neutropenia and recurrent microbial infections, particularly, during advanced disease. However, recent studies have extended the investigation area to cover new aspects of the interactions between HIV-1 and PMNs. This review aims to summarize these advances and address the impact of HIV-1 infection on PMNs as well as the impact of PMNs on HIV-1 disease progression to better understand the pathophysiology of HIV-1 infection.

Critical role of the C5a-activated neutrophils in high-fat diet-induced vascular inflammation

Exceed and chronic high-fat diet (HFD) contributes to the diagnosis and development of atherosclerosis, obesity, and metabolic syndrome. However, the key molecular component(s) triggered by HFD responsible for initiating vascular inflammation remain unknown. We observed that feeding HFD for 4 weeks is sufficient to induce leukocyte recruitment in the femoral artery of wild-type mice. Neutrophil- and monocyte-depletion analyses confirmed the preferential recruitment of neutrophils in these mice. Protein analysis of sera from HFD-fed mice revealed a marked elevation of complement component C5a levels. Exogenous C5a alone induced leukocyte recruitment, which was abolished by a C5a-receptor antagonist. We also examined the role of neutrophil-derived MCP-1 in accumulation of leukocytes in the artery. These results demonstrated a previously unrecognized role for C5a and neutrophils in the early onset of HFD-induced vascular inflammation. Further study may help in elucidating a novel regulatory pathway to control diet-induced inflammation such as that in case of atherosclerosis.

The effect of HIV infection on the host response to bacterial sepsis

Bacterial sepsis is an important cause of morbidity and mortality in patients with HIV. HIV causes increased susceptibility to invasive infections and affects sepsis pathogenesis caused by pre-existing activation and exhaustion of the immune system. We review the effect of HIV on different components of immune responses implicated in bacterial sepsis, and possible mechanisms underlying the increased risk of invasive bacterial infections. We focus on pattern recognition receptors and innate cellular responses, cytokines, lymphocytes, coagulation, and the complement system. A combination of factors causes increased susceptibility to infection and can contribute to a disturbed immune response during a septic event in patients with HIV. HIV-induced perturbations of the immune system depend on stage of infection and are only in part restored by combination antiretroviral therapy. Immunomodulatory treatments currently under development for sepsis might be particularly beneficial to patients with HIV co-infection because many pathogenic mechanisms in HIV and sepsis overlap.

Cathepsin D is released after severe tissue trauma in vivo and is capable of generating C5a in vitro

In response to severe tissue trauma several danger sensing and signalling cascades are activated, including the complement and the apoptosis systems. In polytrauma patients, both the early activation of the complement cascade with an excessive generation of the potent anaphylatoxin C5a and the induction of apoptosis have been shown to modulate the post-traumatic immune response. However, little is known about a direct interaction between the complement and apoptosis systems after severe tissue trauma. Therefore the focus of the present study was to elucidate the interplay between the central complement component C5 and the pro-apoptotic aspartic protease cathepsin D. In vivo, the cathepsin D plasma concentration of multiple injured patients was markedly increased when compared to healthy volunteers. In vitro incubation of C5 with cathepsin D resulted in a concentration- and time-dependent generation of C5a, which was inhibited by the aspartate protease inhibitor pepstatin A. Immunoblotting and sequencing analysis indicated that the C5 cleavage product represents the native form of human C5a, also exhibiting chemotactic activity for human neutrophils. In conclusion, these data show for the first time that cathepsin D is increased in plasma early after severe tissue injury. Furthermore, the results provide in vitro evidence of cleavage of C5 by an aspartic protease with subsequent generation of functional C5a, which represents a new path of complement activation.

HIV and other lentiviral infections cause defects in neutrophil chemotaxis, recruitment, and cell structure: immunorestorative effects of granulocyte-macrophage colony-stimulating factor

Patients with HIV infection exhibit deficits in bacterial and fungal clearance, and possibly depressed innate immunity. In this study, we observed that neutrophils from HIV-infected patients have a profound defect in chemotaxis in response to endogenous (IL-8) and bacterial (fMLP) chemoattractants, which was directly correlated with peripheral CD4(+) lymphocyte levels but not plasma viral load. A similar chemotactic defect was observed in the feline immunodeficiency virus (FIV) model of HIV infection. Intravital microscopy of FIV-infected animals revealed marked impairment in the in vivo recruitment of leukocytes; specifically integrin-dependent neutrophil adhesion and emigration induced by bacterial products. Treatment of FIV-infected animals with GM-CSF re-established both neutrophil recruitment (rolling, adhesion, and emigration) and in vitro chemotaxis to the levels seen in uninfected animals. This restoration of neutrophil responses was not due to GM-CSF-mediated priming. Rather, HIV and FIV infections resulted in defective neutrophil development, with an ensuing reduction in neutrophil granularity and chemotactic receptor expression. GM-CSF therapy restored neutrophil granularity, implying restoration of normal neutrophil development. Together, our findings underscore the fundamental defects in innate immunity caused by lentivirus infections, while also indicating that GM-CSF may be a potential immunorestorative therapy for HIV-infected patients.

Age-related changes in polymorphonuclear neutrophil characteristics in infants born to human immunodeficiency virus type 1 seropositive mothers

In infants, the major components of the innate immune system appear weakened, and it has been shown that both polymorphonuclear neutrophil (PMN) production and function are immature. This study was conducted to assess the expression of a number of receptors important to normal PMN function and the integrity of PMN degranulation in cord blood and in uninfected children of varying ages born to human immunodeficiency virus type 1 (HIV-1) seropositive mothers. Although the expression of l-selectin (CD62L) on PMN did not differ between the infants aged 12, 15 and 18 months, the expression of the interleukin-8 (IL-8) receptors CXCR1 and CXCR2, and the complement 5a (C5a) receptor CD88 displayed a similar pattern, with the highest levels expressed on PMN from infants in the 12 month old age group, and declining with age. It was also observed that PMN from a substantial proportion of the younger infants were unresponsive to a variety of stimuli including IL-8, C5a, stromal cell-derived factor (SDF)-1alpha, SDF-1beta, and phorbol 12-myristate 13-acetate (PMA), with the proportions of children showing positive (adult-like) PMN degranulation responses increasing with age. Exposure to HIV-1 did not appear to be the cause of impaired degranulation responses, since a similar proportion of cord blood PMN from uninfected infants born to HIV-1 infected and HIV-1 uninfected mothers were unresponsive. The altered expression of these important receptors and inefficient agonist-induced degranulation in early life may contribute to the increased susceptibility of infants to secondary microbial infections.

Reduced frequency of wheezing respiratory illness in infants with perinatal human immunodeficiency virus-type 1 infection: a model for immunologic and inflammatory mechanisms of airway obstruction?

A multivariate analysis using a logistic regression model evaluated odds ratio (OR) and 95% confidence limits (95% CL) of pediatrician-diagnosed wheezing respiratory illness in 75 infants with perinatal human immunodeficiency virus-type 1 (HIV-1) infection, 205 uninfected infants of HIV-1 infected mothers, and 1780 infants of HIV-1 uninfected mothers. Infants were prospectively followed-up for the first 2 years of life. Covariates were risk factors for wheezing respiratory illness (preterm delivery, low birth weight, maternal smoking, formula feeding, and neonatal respiratory disorders). Maternal use of illicit drugs in pregnancy, antiretroviral treatment in pregnancy, maternal HIV-1-related clinical condition at the time of delivery were also included in the models when infants of HIV-1 infected mothers were taken into account. Although the frequency of risk factors for wheezing respiratory illness was higher in infants of HIV-1 infected than in those of uninfected mothers, HIV-1 infection emerged as a protective factor [OR: 0.001 (95% CL: 0.0001-0.01); p < 0.001]. The frequency of risk factors was similarly high among infants of infected mothers, but OR was lower in HIV-1 infected than in uninfected infants of infected mothers (0.005; 95% CL: 0.0004-0.06; p < 0.001). Finally, OR was higher in uninfected infants of HIV-1 infected mothers (who evidenced a higher frequency of risk factors) than in infants of HIV-1 uninfected mothers (9.97; 95% CL: 4.87-20.40; p < 0.001). Understanding the reason why HIV-1 protects against wheezing respiratory illness could shed light on the immunologic and inflammatory mechanisms of airway obstruction.

Altered expression of L-selectin (CD62L) on polymorphonuclear neutrophils of children vertically infected with human immunodeficiency virus type 1

The expression of the leukocyte adhesion molecule L-selectin (CD62L) on polymorphonuclear neutrophils (PMN) and circulating levels of the soluble form of the receptor (sCD62L) were determined for a group of HIV-1-infected children, categorized as having mild or severe disease, and a group of uninfected control children. The fluorescence intensity of CD62L on PMN was significantly reduced in the HIV-1-infected children with mild disease compared to the uninfected controls. The proportion of lymphocytes expressing CD62L, as well as their corresponding fluorescence intensities, was significantly reduced in both the mild and the severe disease groups compared to the uninfected children, while peripheral levels of sCD62L were significantly elevated in the HIV-1-infected children with mild and severe disease compared to the controls. Altered cell migration resulting from reduced expression of CD62L may be an important contributor to the increased susceptibility to secondary microbial infections seen in HIV-1-infected children.