Hypoxemia modifies circulating and exudate neutrophil number and functional responses in carrageenin-induced pleurisy in the rat.

To assess the effect of hypoxemia on the responses of polymorphonuclear neutrophils (PMN) during an inflammatory response, rats were maintained in a low F1O2 atmosphere (9% O2) or room air for 12 h before intrathoracic injection of carrageenin or intradermal injections of agonists. After 4 h, hypoxemic rats had 50% more circulating PMN in blood and 25% less PMN in pleural exudate, whereas the number of PMN in skin biopsies did not differ from controls. Following hypoxemia, basal adhesion of blood PMN to serum-coated plastic wells was unchanged, whereas fMLP-stimulated adhesion was 50% greater. In contrast, basal adhesion of exudate PMN was 72% greater. In hypoxemic rats, exudate PMN produced 64% more PMA-stimulated superoxide than blood PMN; furthermore, blood and exudate PMN produced 4.5- and 2-fold more LPS-stimulated nitric oxide than controls, respectively. These results show that a moderate level of hypoxemia may trigger mechanisms that will interfere with PMN emigration yet prime these cells for enhanced responses upon stimulation.

Priming and induction of eosinophil trafficking in guinea-pig cutaneous inflammation by tumour necrosis factor alpha.

Tissue eosinophilia is a hallmark of allergic and parasitic diseases. Priming mechanisms may play an important role in mediating the process of eosinophil accumulation in these conditions. We have previously shown that blockade of tumour necrosis factor alpha (TNFalpha) inhibited the capacity of lipopolysaccharide to prime skin sites for chemoattractant-induced eosinophil recruitment. The present study was carried out to investigate the capacity of TNFalpha to prime an inflammatory site for enhanced eosinophil accumulation. Initial experiments investigated the capacity of TNFalpha itself to induce eosinophil accumulation. Intradermal injection of murine TNFalpha (10-300 ng per site) in the guinea-pig induced significant accumulation of 111In-eosinophils. Kinetic studies showed the response to be delayed in onset and inhibited by cycloheximide, consistent with a dependency on protein synthesis. Trafficking of 111In-eosinophils to sites treated for 2 h with TNFalpha (10-100 ng per site) was inhibited by monoclonal antibodies (mAbs) against beta2 or alpha4 integrins. Intradermal injection of a low dose (3 ng) of TNFalpha (which by itself had no significant effect on eosinophil trafficking) prior to chemoattractants or antigen in sensitized skin sites, induced significant priming of eosinophil accumulation. Recruitment of both 111In-eosinophils and endogenous eosinophils was enhanced. Trafficking to TNFalpha-primed responses was dependent on protein synthesis and beta2 integrins. In contrast, the alpha4 integrin mAb failed to inhibit the TNFalpha primed response. Thus, TNFalpha can induce and also prime eosinophil recruitment in guinea-pig skin. Our results provide further evidence that this cytokine may be an important mediator of allergic- or parasite-induced eosinophilic inflammation.

A comparison of the inhibitory activity of PDE4 inhibitors on leukocyte PDE4 activity in vitro and eosinophil trafficking in vivo.

1. Phosphodiesterase (PDE) 4 inhibitors have been shown to inhibit eosinophil PDE4 activity in vitro and accumulation of eosinophils in experimental airways inflammation. However, direct effects on eosinophil trafficking have not been studied in detail and it is not known if activity in vitro translates into efficacy in vivo. In the present study, we compared the activity of five PDE4 inhibitors in vitro and against trafficking of (111)In-eosinophils in cutaneous inflammation in the guinea-pig. 2. The rank order of potency for inhibition of PDE4 activity in guinea-pig eosinophil, neutrophil and macrophage, and human neutrophil lysates was RP73401 > SB207499 >CDP840 > rolipram > LAS31025. On TNFalpha production by human PBMC, all inhibitors with the exception of rolipram showed potency similar to their effect on neutrophil lysates. 3. In a brain cerebellum binding assay, the rank order of potency at displacing [3H]-rolipram was RP73401 > rolipram > SB207499 > CDP840 > LAS30125. 4. Trafficking of (111)In-eosinophils to skin sites injected with PAF, ZAP or antigen in sensitized sites was inhibited by oral administration of all PDE4 inhibitors. The rank order of potency was RP73401 = rolipram > LAS31025 > SB207499 > CDP840. 5. With the exception was RP73401, which was the most potent compound in all assays, there was no clear relationship between activity of PDE4 inhibitors in vitro and capacity to inhibit eosinophil trafficking in vivo. Thus, we conclude that in vitro activity of PDE4 inhibitors does not predict in vivo efficacy in an experimental model of eosinophil trafficking.

Priming of eosinophil recruitment in vivo by LPS pretreatment.

Eosinophils are important inflammatory cells in allergic diseases. Recent evidence suggests that priming mechanisms in the blood may be important for effective eosinophil recruitment to sites of allergic inflammation. We have investigated whether priming an inflammatory site could enhance eosinophil recruitment in vivo. Pretreatment of skin sites in the guinea pig with a low dose (30 ng) of LPS, which had little effect on eosinophil accumulation alone, enhanced by up to threefold the 111In-eosinophil accumulation in response to a passive cutaneous anaphylactic reaction and to intradermally injected eosinophil chemoattractants (leukotriene B4, PAF, and C5ades Arg). In contrast, LPS pretreatment did not enhance accumulation of 111In-neutrophils. Priming was seen only with a 1-h pretreatment time and was not associated with an increase in local edema or a change in cutaneous blood flow. It was independent of local protein synthesis, as assessed using cycloheximide, and was unaffected by a PAF antagonist, a 5-lipoxygenase inhibitor, and the IL-1 receptor antagonist. The priming response was, however, reduced by co-injection with the LPS of TNFR-IgG, but not of CD4-IgG. Blockade of CD18 showed this adhesion molecule to be critical for eosinophil accumulation, and LPS-primed sites were inhibited as effectively as nonprimed sites. In conclusion, low dose LPS pretreatment of guinea pig skin sites primes for eosinophil accumulation induced by intradermally injected inflammatory mediators and cutaneous anaphylactic reaction. This may be an important process by which eosinophil recruitment is modulated in vivo.