Effect of immunological stimulation on the production of platelet-activating factor by rat peritoneal cells: its relevance to anaphylactic reactions

Immunoglobulin-E/dinitrophenyl complexes induce nitric oxide synthesis in rat peritoneal macrophages by a mechanism involving CD23 and NF-kappa B activation

The production of nitric oxide (NO) by rat adherent peritoneal cells stimulated with preformed IgE/Dinitrophenyl-BSA (DNP-BSA) complexes and its dependence on the activation of the transcription factor NF-kappa B were studied. Stimulation with IgE/DNP-BSA complexes at equivalence induced both the production of NO and an increased expression of the inducible isoform of NO synthase (iNOS) protein. Both events were also elicited by a rabbit polyclonal F(ab')2 anti-CD23 cross-reacting with rat CD23, thus suggesting Fc epsilon RII/CD23 antigen as the IgE-binding structure involved in the triggering of the response and ruling out an interaction of the antibody via its Fc portion. Inhibition of redox-sensitive signaling mechanisms by the antioxidant pyrrolidine dithiocarbamate (PDTC) blocked NO production, iNOS expression, and NF-kappa B activation elicited by both IgE/DNP-BSA complexes and anti-CD23 F(ab')2, thus suggesting the involvement of NF-kappa B in the signaling pathway leading to the transcriptional activation of iNOS. These results show the existence in rat peritoneal macrophages of a signaling pathway triggered by CD23 engagement that promotes nuclear translocation of NF-kappa B and transcriptional activation of the inducible isoform of NO synthase.

Strain-dependency of leukotriene C4 generation from isolated lungs of immunized mice

1. The antigen-induced leukotriene C4 (LTC4)-like-material release from isolated perfused lungs of actively sensitized Swiss, Balb/C and CBA/J mice was compared. The intra-tracheal (i.t.) instillation of 1 and 100 micrograms ovalbumin to lungs from Swiss mice was followed by a dose-dependent generation of LTC4-like material into the effluent, as detected by radio-immunoassay and h.p.l.c., followed by an enzyme-immunoassay. In contrast, lungs from sensitized Balb/C and CBA/J mice failed to exhibit LTC4-like-material release in amounts above the basal values. No histamine secretion was observed when lungs of the three strains of mice were challenged with ovalbumin. 2. The i.t. instillation of 1 or 10 micrograms platelet-activating factor (PAF) or of 100 micrograms arachidonic acid to lungs from non-sensitized mice, induced the release of comparable amounts of LTC4-like-material in the effluent, irrespective to the strain. However, N-formyl-L-methionyl-L-leucyl-L- phenylalanine (fMLP, 0.1, 10 micrograms), was more effective in inducing the release of LTC4-like-material from lung from Swiss and CBA, than from Balb/C, mice. 3. The intraplantar injection of 0.01 microgram ovalbumin to sensitized Swiss mice induced an intense oedema formation, as measured plethysmographically, while Balb/C mice required a dose of antigen at least 10 fold higher for a similar response. CBA/J mice did not respond to antigen challenge in terms of oedema formation. The intraplantar injection of PAF or fMLP to non-immunized mice induced an oedema of similar intensity in all the strains considered. Accordingly, the different responses to ovalbumin of the three strains of mice is not accounted for by different paw responsiveness to inflammatory mediators.4. Swiss and CBA/J mice exhibited higher titers of circulating IgG antibodies, as measured by passive cutaneous anaphylaxis (PCA), than Balb/C mice. Conversely, lower IgE titers were measured in the serum of sensitized Swiss and CBA/J mice, as compared to Balb/C.5. Our results demonstrate a strain-dependency of antigen-induced LTC4 release from lungs from sensitized mice. This difference is related to the ability of sensitized animals to develop immediate hypersensitivity responses, such as paw oedema formation, but not to the antibody subclass involved in the immunization. Strain-dependent factors may influence the intensity of the response to antigen stimulation. It is thus essential to characterize the different components of the immune response when mouse models for studying hypersensitivity reactions are developed.

Study of the effector mechanism involved in the production of haemorrhagic necrosis of the small intestine in rat passive anaphylaxis

1. The effector mechanism of intestinal necrosis in rat anaphylaxis was studied following several complementary approaches: (i) the use of monoclonal antibodies (mAb) belonging to different classes (IgG1, IgG2b and IgE anti-DNP), (ii) the assay of mediators, and (iii) the use of pharmacological tools. 2. Lethality and haemorrhagic necrosis of the small intestine were observed in IgE-sensitized rats, whereas IgG mAb produced milder physiological disturbances. 3. Inhibition of leukotriene biosynthesis reduced the drop of systemic blood pressure (BP) and the extent of protein-rich plasma exudation but it did not influence the haemorrhagic component of intestinal necrosis. 4. The antihistamine, pyrilamine, partially diminished the haemorrhagic component of the intestinal necrosis. 5. The involvement of mediators related to platelet-activating factor (PAF) was studied by examining the pharmacological effects of these autacoids and of PAF-receptor antagonists (PCA4248, UR12460 and BB823). PAF induced intestinal lesions similar to those observed in IgE-sensitized rats and PAF-receptor antagonists markedly decreased haemorrhage in IgE-sensitized rats. 6. PAF levels were transiently increased after dinitrophenol (DNP)- bovine serum albumin (BSA) challenge in the small intestine of IgE-sensitized rats. 7. These data stress differences in the outcome of anaphylaxis related to the type of receptors for the Fc portion of immunoglobulins that are involved. IgE is the antibody class that elicits the most severe response due to the activation of mast cells via Fc epsilon RI (surface receptors that bind IgE antibodies with high affinity), and the only one able to produce intestinal haemorrhagic necrosis. 8. The mast-cell-derived mediators PAF/acyl-PAF and histamine, most probably associated with tumour necrosis factor alpha/cachectin (TNF-alpha), seem to play a central role in the production of the vascular changes required for the extravasation of erythrocytes in the small intestine mucosa.