In neutrophils, coupling of chemoattractants to their cell surface receptor at low temperature (<15°C) leads to receptor deactivation/desensitization without any triggering of the superoxide anion-generating NADPHoxidase. We show that the deactivated formyl peptide receptors (FPRs) can be reactivated/resensitized by the cytoskeleton-disrupting drug cytochalasin B. Such cytoskeleton-dependent receptor reactivation occurs also with the closely related receptors FPR-like-1 and C5aR but not with the receptors for interleukin-8 and plateletactivating factor. The reactivation state was further characterized with FPR as a model. The signals generated by receptor reactivation induced superoxide production that was terminated in 5-8 min, after which the neutrophils entered a new state of homologous deactivation. FPR antagonists were potent inhibitors of the superoxide production induced by the reactivated receptors, suggesting that the occupied receptors turn into an actively signaling state when the cytoskeleton is disrupted. The signals generated by the reactivated receptor were pertussis toxin-sensitive, indicating involvement of a G-protein. However, no transient elevation of intracellular Ca 2؉ accompanies the NADPH-oxidase activation. This was not due to a general down-regulation of phospholipase C/Ca 2؉ signaling, and despite the fact that no intracellular Ca 2؉ transient was generated, protein kinase C still appeared to be involved in the response. Further, phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and MEK all participated in the generation of second messengers from the reactivated receptors.

The eosinophil granulocyte is an inflammatory cell involved in allergic diseases such as asthma and rhinitis. Eosinophil cationic protein (ECP) is a basic and potentially cytotoxic granule protein that is released from the eosinophil upon activation. The aim was to study secretion of molecular variants of ECP from blood eosinophils with the hypothesis that the stored noncytotoxic ECP is altered into cytotoxic species upon release from the cell. Eosinophil granulocytes were purified to &gt;95% from venous blood from birch pollen allergic subjects, with symptoms of rhinitis, and from healthy control subjects during the birch pollen season. The cells were stimulated with IL-5, GM-CSF, or serum-opsonized Sephadex particles. Concentration of ECP in cells or supernatants was measured by means of a fluoroenzyme immunoassay, and ECP heterogeneity was studied using an affinity capture assay with the surface-enhanced laser desorption/ionization-time of flight mass spectrometry technique. Extracts of unstimulated eosinophils contained 10 major ECP variants, with molecular masses ranging from 16.1 to 17.7 kDa. Stimulation with particles mainly induced the secretion of two molecular variants at 16.1 and 16.3 kDa, while cytokine stimulation gave rise to a different secretion profile. ECP variants in the pellet extracts remained unaffected by cell activation. The modifications of secreted ECP were partly explained by differences in N-linked glycosylations. Secretion of ECP from eosinophils involves protein modification. The molecular masses of released ECP have acquired the masses of the cytotoxic species.

Eosinophil cationic protein (ECP), a secretory protein of the eosinophil granulocyte, is a basic and highly heterogeneous protein. This heterogeneity is dependent on polymorphisms in the ECP gene and post-translational modifications, and it affects the functional properties of the protein in terms of cytotoxicity. The aim of this study was to further investigate the molecular heterogeneity, hence, an affinity capture assay based on an antigen-antibody interaction with the surface-enhanced laser desorption/ionization-time of flight mass spectrometry (SELDI-TOF MS) technique was developed. Of three monoclonal antibodies tested, that is, EG2, 614, and 652, the 614 mab was chosen for the experiments. ECP heterogeneity of single individuals was studied in extracts of purified blood eosinophils, and the presence of approximately 5 major molecular species was demonstrated in each subject. ECP from subjects with different ECP 434(G>C) genotypes (arg97thr) showed mass differences corresponding to the amino acid shift from arginine to threonine. ECP purified from pooled leukocytes of large numbers of healthy blood donors demonstrated an extensive mass heterogeneity with approximately 10 major molecular species. By the use of a variety of glucosidases it was shown that this heterogeneity was mainly due to N-linked oligosaccharides on which sialic acid, galactose, and acetylglucosamine was positioned. We conclude that the SELDI-TOF MS technique using specific monoclonal antibodies is a convenient and versatile tool; by means of this technique, we could detect both genetic and post-translational causes of the molecular heterogeneity of the eosinophil cationic protein.

We conclude that the eosinophils of birch pollen allergic patients have reduced production of oxygen radicals when the patients are exposed to their allergen, which could depend on higher amounts of hypodense eosinophils in the blood during season.

Blood eosinophils from allergic patients are primed in vivo, as compared to eosinophils from non-allergic controls, during a pollen season. Interleukin-5 primes equally the PMA-induced oxidative metabolism of human eosinophils from healthy or allergic subjects. The mechanism of IL-5 priming after PMA stimulation of oxygen radical production is MEK independent.