Cross reactivity between European hornet and yellow jacket venoms.

BACKGROUND: Cross-reactions between venoms may be responsible for multiple diagnostic positivities in hymenoptera allergy. There is limited data on the cross-reactivity between Vespula spp and Vespa crabro, which is an important cause of severe reactions in some parts of Europe. We studied by CAP-inhibition assays and immunoblotting the cross-reactivity between the two venoms. METHODS: Sera from patients with non discriminative skin/CAP positivity to both Vespula and Vespa crabro were collected for the analyses. Inhibition assays were carried out with a CAP method, incubating the sera separately with both venoms and subsequently measuring the specific IgE to venoms themselves. Immunoblotting was performed on sera with ambiguous results at the CAP-inhibition. RESULTS: Seventeen patients had a severe reaction after Vespa crabro sting and proved skin and CAP positive also to vespula. In 11/17 patients, Vespula venom completely inhibited IgE binding to VC venom, whereas VC venom inhibited binding to Vespula venom only partially (<75%). In 6 subjects the CAP-inhibition provided inconclusive results and their sera were analysed by immunoblotting. The SDS-PAGE identified hyaluronidase, phospholipase A1 and antigen 5 as the main proteins of the venoms. In 5 sera the levels of IgE against antigen 5 of Vespa crabro were higher than IgE against Vespula germanica, thus indicating a true sensitisation to crabro. CONCLUSION: In the case of multiple positivities to Vespa crabro and Vespula spp the CAP inhibition is helpful in detecting the cross-reactivities.

Nerve growth factor inhibits apoptosis in memory B lymphocytes via inactivation of p38 MAPK, prevention of Bcl-2 phosphorylation, and cytochrome c release.

Survival of memory B lymphocytes is tightly linked to the integrity of the Bcl-2 protein and is regulated by a nerve growth factor (NGF) autocrine circuit. In factor-starved memory B cells, the addition of exogenous NGF promptly induced p38 mitogen-activated protein kinase (MAPK), but not c-Jun N-terminal kinase (JNK), dephosphorylation. Conversely, withdrawal of endogenous NGF was followed by p38 MAPK activation and translocation onto mitochondria, whereby it combined with and phosphorylated Bcl-2, as assessed by co-immunoprecipitation and kinase assays in vivo and in vitro. Mitochondria isolated from human memory B cells, then exposed to recombinant p38 MAPK, released cytochrome c, as did mitochondria from Bcl-2-negative MDCK cells loaded with recombinant Bcl-2. Apoptosis induced by NGF neutralization could be blocked by the specific p38 MAPK inhibitor SB203580 or by Bcl-2 mutations in Ser-87 or Thr-56. These data demonstrate that the molecular mechanisms underlying the survival factor function of NGF critically rely upon the continuous inactivation of p38 MAPK, a Bcl-2-modifying enzyme.

Interferon-alpha-induced inhibition of B16 melanoma cell proliferation: interference with the bFGF autocrine growth circuit.

The molecular mechanisms underlying the growth inhibition induced by interferon-alpha (IFN-alpha) in B16 murine melanoma cells were investigated. IFN-alpha did not induce cell apoptosis, but strongly interfered with the synthesis of basic fibroblast growth factor (bFGF), which acts as an autocrine growth factor in this system. Inhibition of bFGF synthesis was observed at the same concentrations (50-500 pM, 10-100 U/ml) of IFN-alpha able to induce growth arrest of B16 melanoma cells. Although the synthesis of acidic (a)FGF was only slightly affected by IFN-alpha, the cytokine induced release of an aFGF-related low-molecular-weight peptide, which was able to interfere with bFGF binding to surface receptors. Thus, the molecular mechanisms of IFN-alpha activity on melanoma cells include a specific modulation of the bFGF autocrine circuit.

Interleukin-4 rapidly down-modulates the macrophage colony-stimulating factor receptor in murine macrophages.

The activation of macrophages interferes with their response to macrophage colony-stimulating factor (M-CSF), the main growth and differentiation factor for mononuclear phagocytes. We tested the rapid effects of interleukin-4 (IL-4), the alternative macrophage activator produced by Th2 helper lymphocytes, on the receptor for M-CSF (M-CSFR) expressed on the cell surface of murine macrophages. IL4 rapidly down-modulated M-CSFR in a dose-dependent fashion. This effect was unique to IL-4 among a number of Th2-produced cytokines, none of which, with the exception of IL4 itself, is able to activate macrophages. The down-modulation of M-CSFR by IL4 was partially prevented by the inhibition of the activity of phospholipase C or protein kinase C. The data are consistent with the hypothesis that the down-modulation of M-CSFR is a property common to, and exclusive of, macrophage activators, and is driven by different activators via a common mechanism.

Interleukin 2 down-modulates the macrophage colony-stimulating factor receptor in murine macrophages.

Macrophage colony-stimulating factor (M-CSF) is the main growth factor for mononuclear phagocytes. Responsiveness to growth factors is reduced in the course of functional activation of macrophages. We studied the interference of the macrophage activator interleukin 2 (IL-2) with the response to M-CSF, in macrophages of the M-CSF-dependent murine line BAC-1.2F5. Long-term effects of IL-2 on cell growth were determined, showing that IL-2 reduces the M-CSF-dependent proliferation of macrophages. Short-term effects of IL-2 on the expression of the receptor for M-CSF (M-CSF.R) were characterized in more detail. IL-2 rapidly down-modulated M-CSF.R in a dose-dependent fashion, and interferon-gamma and lipopolysaccharides synergized with IL-2 in this modulation. The IL-2-induced down-modulation of M-CSF.R was shown to require the activity of protein-kinase-C and phospholipase-C. The data are consistent with the hypothesis that the down-modulation of M-CSF.R is a general property of macrophage activators.

Nerve growth factor is an autocrine survival factor for memory B lymphocytes.

Production of nerve growth factor (NGF) was assessed in cultures of human T and B lymphocytes and macrophages. NGF was constitutively produced by B cells only, which also expressed surface p140trk-A and p75NGFR molecules and hence efficiently bound and internalized the cytokine. Neutralization of endogenous NGF caused disappearance of Bcl-2 protein and apoptotic death of resting lymphocytes bearing surface IgG or IgA, a population comprising memory cells, while surface IgM/IgD "virgin" B lymphocytes were not affected. In vivo administration of neutralizing anti-NGF antibodies caused strong reduction in the titer of specific IgG in mice immunized with tetanus toxoid, nitrophenol, or arsonate and reduced numbers of surface IgG or IgA B lymphocytes. Thus, NGF is an autocrine survival factor for memory B lymphocytes.