Chemotactic responsiveness of eosinophils isolated from patients with inflammatory skin diseases

Neuropeptide-induced chemotaxis of eosinophils in pulmonary diseases

Eosinophilic lung diseases include various disease entities, and the incidence of pulmonary infiltration with eosinophilia is on the rise. Because eosinophils, well known as inflammatory cells, respond to peripheral neuropeptides in vitro and in vivo, and these peptides are also present in human airway nerves, their interactions are thought to play a major role in the initiation and perpetuation of inflammatory lung diseases. This article reviews the current literature on eosinophil biology and interactions of these cells with the neuroendocrine system. Also, implications of tachykinins and other neuropeptides in eosinophilic pulmonary diseases is discussed based on recently investigated mechanisms. Eosinophils and sensory nerves most likely influence each other in a two-directional way in the pathogenesis of pulmonary diseases. Although release of sensory neuropeptides is involved in most conditions of airway hyperresponsiveness, increased bronchial resistance, and lung eosinophilia, the role of these nervous system-derived mediators in pulmonary diseases may be underestimated.

Differences in eosinophil and neutrophil chemotactic responses in sowda and generalized form of onchocerciasis

Extravasation of host's leukocytes from blood vessels into inflammatory tissues represents a prerequisite for a subsequent interaction with invaded parasites. The migratory responses of eosinophilic and neutrophilic granulocytes in the polar forms of the filarial infection onchocerciasis were investigated. The hyporeactive, generalized form, the chronic hyperreactive (sowda) form and persons without signs of onchocerciasis from a hypoendemic area for onchocerciasis were compared. Eosinophils from sowda patients responded more strongly to the inflammatory mediator platelet-activating factor (PAF) than those from generalized patients and persons without onchocerciasis. The most significant differences were found between the sowda group and a subgroup of the generalized form with 16-80 microfilariae/mg skin (P<0.05) while patients with low microfilarial density exhibited chemotactic responses similar to the sowda group. In contrast to the strong eosinophil response, neutrophils from sowda patients appeared unreactive to PAF and the tripeptide activator formyl-methionyl-leucyl-phenylalanine (fMLP), thereby differing from both other groups. Laboratory data confirmed a state of hyperreactivity in sowda patients similarly found in generalized patients with low microfilarial density and contrasting with those with a microfilarial density of 16-80 mf/mg. The results revealed an inverse chemotactic responsiveness of eosinophil and neutrophil granulocytes in sowda patients and strengthened the observation of a spectrum of host's responsiveness in onchocerciasis.

C3a is a chemotaxin for human eosinophils but not for neutrophils. I. C3a stimulation of neutrophils is secondary to eosinophil activation

Inflammatory action of the potent chemotaxin C5a has been well characterized on a variety of human cell types, including neutrophils, monocytes, basophils, and eosinophils. The cellular effects of C3a are less well defined. Contradictory reports have been published for C3a activation of neutrophils. Recent reports that C3a activates both basophils and eosinophils prompted us to reinvestigate the effects of C3a stimulation on eosinophils. We hypothesized that C3a activation of eosinophils, cells that are present in most neutrophil preparations, might lead to neutrophil activation. Using neutrophils of 98% purity, we observed no evidence of cellular activation after stimulation with either C3a, recombinant human C3a (rhC3a), or the synthetic C3a analogue C3a 57-77, Y57. Eosinophils purified to > 98% purity displayed concentration-dependent polarization, chemotaxis, and enzyme release by stimulation with C3a, rhC3a, and the synthetic C3a analogue. An inactive form of C3a, C3adesArg, failed to stimulate either eosinophils or neutrophils. Using neutrophil preparations containing 5-9% eosinophils, up to 20% of neutrophils became polarized after exposure to C3a. Likewise, we demonstrated that supernatant from C3a-stimulated eosinophils promotes neutrophil chemotaxis. Eosinophil polarization experiments were repeated in the presence of antibody to the C5a receptor (C5aR) to show that C3a and C5a interact with different receptors. C3a activates eosinophils in the presence of anti-C5aR antibody at concentrations that fully block C5a activation. We conclude that eosinophils are directly activated by either C3a or C5a, whereas C3a failed to activate neutrophils. C3a acts on eosinophils via a receptor that is distinct from C5aR. Since neutrophils are indirectly stimulated by C3a, eosinophils contaminating neutrophil preparations may explain earlier reports that C3a activates human neutrophils.

Monocyte adhesion to fibronectin in psoriasis

BACKGROUND

After vascular extravasation, mononuclear cells (MNC) undergo chemotaxis and adhesion to extracellular matrix proteins, resulting in their differentiation into macrophages. Although endothelial adhesion and chemotaxis are altered in psoriasis, MNC adhesion to extracellular matrix proteins has not been previously studied in the disease. Since MNC adhesion to endothelial cells is abnormally regulated in psoriasis by TGF-beta, we tested they hypothesis that in psoriasis substance P also regulates the adhesion of monocytes to the extracellular matrix protein fibronectin.

METHODS

Monocytes from 16 normal controls and 11 psoriatic individuals were isolated and purified using a two-step gradient centrifugation procedure. Adhesion to fibronectin was studied by plating monocyte suspensions onto fibronectin-precoated microtiter plates. The number of adherent cells was quantified by measuring their hexosaminidase activity.

RESULTS

Although statistically significant differences in the basal (unstimulated) adhesion or in the substance P-stimulated adhesion between normal control monocytes and those obtained from psoriatic individuals were not observed, a subpopulation of psoriatics was identified who responded to substance P. Furthermore, this in vitro response to substance P was correlated with the clinical status of the subpopulation which was characterized by unstable psoriasis triggered by stressful life events.

CONCLUSIONS

The results of this study indicate that priming of monocytes by the extracellular matrix protein fibronectin or by elevated levels of substance P are not critical steps in the pathogenesis of stable, chronic psoriasis. Substance P may contribute to the appearance of new lesions in some individuals with unstable psoriasis.

Interleukin-8 is a chemo-attractant for eosinophils purified from subjects with a blood eosinophilia but not from normal healthy subjects

Interleukin-8 (IL-8), a pro-inflammatory cytokine with potent neutrophil chemotactic activity, was studied for its effect on eosinophil migration responses, in vitro. Normal density eosinophils were isolated from healthy, non-atopic subjects (<0.35 x 10(9) eosinophils/l) and individuals with various diseases associated with a blood eosinophilia (range 0.56 x 10(9)-12.2 x 10(9) eosinophils/l). IL-8 produced a dose-dependent migrational response for eosinophils from subjects with an eosinophilia, optimal at 10(-8) M (P < 0.01) and the major component of the migrational response was chemokinesis. On a molar basis, IL-8 (EC50 approximately 10(10) M) was 100-fold more potent than platelet activating factor (PAF), although a comparison of the migrational responses showed that at optimal concentrations IL-8 (10(-8) M) produced only 30% maximal responses stimulated by PAF (10(-6) M). In contrast, IL-8 tested over a wide concentration range had a negligible effect on eosinophils from normal subjects. A direct correlation between the total blood eosinophil counts for all subjects and the absolute magnitude of the migrational response to IL-8 (r = 0.727, P < 0.01 at 10(-8) M), PAF (r = 0.551, P < 0.03 at 10(-6) M) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) (r = 0.689, P < 0.02 at 10(-8) M), suggested that heightened eosinophil migrational responses to inflammatory mediators may arise as a consequence of in vivo priming mechanism(s) associated with the development of an eosinophilia. In this regard, eosinophils derived from human cord blood mononuclear cells cultured in the presence of eosinophilopoietic cytokines IL-3 and IL-5, produced migrational responses to IL-8 and PAF, that were comparable with that of eosinophils from eosinophilic subjects. Furthermore, incubation of eosinophils from normal donors with IL-5 (optimal concentration 10(-9) M), significantly enhanced the subsequent migrational responses to both IL-8 (10(-8) M, P < 0.01) and PAF (10(-8) M, P < 0.05). Therefore, the increased responsiveness of eosinophils from eosinophilic subjects may reflect in vivo priming by IL-5 and this phenomenon may contribute partly to the mechanism(s) by which eosinophils preferentially accumulate at sites of allergic inflammation.

The role of eosinophils in the pathogenesis of atopic dermatitis--eosinophil granule proteins as markers of disease activity

Currently, there is a large body of evidence that atopic dermatitis (AD) has an immunologic basis. Atopy-specific helper T cells (Th2-like T cells) may play a pathogenetic role by producing and releasing cytokines relevant for the allergic inflammation, such as IL-4, IL-5, and other growth factors. Eosinophils are believed to be of major importance as effector cells mediating the pathogenetically relevant late-phase reaction which is associated with a significant destruction of the surrounding tissue. Accordingly, a significant preactivation of peripheral blood eosinophils was detected in AD patients, leading to an enhanced susceptibility of these cells to distinct stimuli such as IL-5. Toxic proteins, such as eosinophil cationic protein (ECP), contained in the matrix and the core of secondary granules of eosinophils, may play an important role by propagating the allergic inflammatory process and by modulating the immune response. The pathogenetic role of eosinophils in AD is further supported by the detection of these proteins in the eczematous skin of patients. Furthermore, recent data point to a significant correlation between disease activity and deposition of eosinophil granule content: ECP serum levels were significantly increased in AD patients. In addition, ECP levels correlated with the disease activity. Moreover, clinical improvement was associated with a decrease of both the clinical score and serum ECP levels. These data clearly indicate that activated eosinophils may play a major role in the allergic inflammatory process of AD. Therefore, modulation of eosinophil activation could prove to be an important pharmacologic modality for the treatment of AD.