The inositol-1,2-cyclic phosphate moiety of the cross-reacting determinant, carbohydrate chains, and proteinaceous components are all responsible for the cross-reactivity of trypanosome variant surface glycoproteins.

Salivarian trypanosomes evade the host immune system by continually swapping their protective variant surface glycoprotein (VSG) coat. Given that VSGs from various trypanosome stocks exhibited cross-reactivity (Camargo et al., Vet. Parasitol. 207, 17-33, 2015), we analyzed here which components are the antigenic determinants for this cross-reaction. Soluble forms of VSGs were purified from four Venezuelan animal trypanosome isolates: TeAp-N/D1, TeAp-ElFrio01, TeAp-Mantecal01, and TeGu-Terecay323. By using the VSG soluble form from TeAp-N/D1, we found that neither the inositol-1,2-cyclic phosphate moiety of the cross-reacting determinant nor the carbohydrate chains were exclusively responsible for its cross-reactivity. Then, all four purified glycoproteins were digested with papain and the resulting peptides were separated by high-performance liquid chromatography. Dot blot evaluation of the fractions using sera from trypanosome-infected animals yielded peptides that possessed cross-reaction activity, demonstrating for the first time that proteinaceous epitopes are also responsible for the cross-reactivity of trypanosome VSGs.

New insights into early and late onset subgroups of preeclampsia from longitudinal versus cross-sectional analysis of urinary inositol-phosphoglycan P-Type.

Most pre-eclampsia (PE) studies have used cross-sectional data to derive conclusions regarding the pathophysiology of the condition. This has led to the concept that there exists early (<34 weeks) and late-onset (>34 weeks) disease according to gestational age at diagnosis. Survival time models have predicted that if the pregnancy was to continue indefinitely, all women would develop PE. In this study we have performed a longitudinal analysis of the urinary biomarker, inositol phosphoglycan (IPG), in a cohort of women giving birth in Mauritius (n-920). We have analysed the PE data in the traditional cross-sectional manner for n = 77 women who developed PE and also then looked at the longitudinal data for 71/77 of the same women. The data allows us to use longitudinal values to calculate a date of onset (first presence of biomarker in urine) and compare that to date of clinical diagnosis (cross sectional). We find two populations for both analysis consistent with an early and late stage subgroup. The calculated date of onset had subgroups (early and late) at 28.4 ±â€¯0.41 weeks and 35.37 ±â€¯0.26 weeks and for clinical date of diagnosis, 32.3 ±â€¯0.59 weeks and 37.04 ±â€¯0.62 weeks, respectively. The presence of the same biomarker in both subgroups and its ability to predict clinical onset 2-4 weeks prior to clinical diagnosis suggest that both groups may have similar aetiology.

Metabolic Phenotypes of Response to Vaccination in Humans.

Herpes zoster (shingles) causes significant morbidity in immune compromised hosts and older adults. Whereas a vaccine is available for prevention of shingles, its efficacy declines with age. To help to understand the mechanisms driving vaccinal responses, we constructed a multiscale, multifactorial response network (MMRN) of immunity in healthy young and older adults immunized with the live attenuated shingles vaccine Zostavax. Vaccination induces robust antigen-specific antibody, plasmablasts, and CD4+ T cells yet limited CD8+ T cell and antiviral responses. The MMRN reveals striking associations between orthogonal datasets, such as transcriptomic and metabolomics signatures, cell populations, and cytokine levels, and identifies immune and metabolic correlates of vaccine immunity. Networks associated with inositol phosphate, glycerophospholipids, and sterol metabolism are tightly coupled with immunity. Critically, the sterol regulatory binding protein 1 and its targets are key integrators of antibody and T follicular cell responses. Our approach is broadly applicable to study human immunity and can help to identify predictors of efficacy as well as mechanisms controlling immunity to vaccination.

Inositol tetrakisphosphate limits NK cell effector functions by controlling PI3K signaling.

Natural killer (NK) cells have important functions in cancer immunosurveillance, BM allograft rejection, fighting infections, tissue homeostasis, and reproduction. NK cell-based therapies are promising treatments for blood cancers. Overcoming their currently limited efficacy requires a better understanding of the molecular mechanisms controlling NK cell development and dampening their effector functions. NK cells recognize the loss of self-antigens or up-regulation of stress-induced ligands on pathogen-infected or tumor cells through invariant NK cell receptors (NKRs), and then kill such stressed cells. Two second-messenger pathways downstream of NKRs are required for NK cell maturation and effector responses: PIP(3) generation by PI3K and generation of diacylglycerol and IP(3) by phospholipase-Cγ (PLCγ). In the present study, we identify a novel role for the phosphorylated IP(3) metabolite inositol (1,3,4,5)tetrakisphosphate (IP(4)) in NK cells. IP(4) promotes NK cell terminal differentiation and acquisition of a mature NKR repertoire. However, in mature NK cells, IP(4) limits NKR-induced IFNγ secretion, granule exocytosis, and target-cell killing, in part by inhibiting the PIP(3) effector-kinase Akt. This identifies IP(4) as an important novel regulator of NK cell development and function and expands our understanding of the therapeutically important mechanisms dampening NK cell responses. Our results further suggest that PI3K regulation by soluble IP(4) is a broadly important signaling paradigm.

[Cloning, expression and immune function analysis of a gene encoding inositol monophosphate in Schistosoma japonicum].

OBJECTIVE: To clone and express a full-length cDNA encoding inositol monophosphate of Schistosoma japonicum (SjIM), and to access its immunoprotection in BALB/c mice for schistosomisis. METHODS: A full-length cDNA encoding the S. japonicum inositol monophosphate was isolated from 42 d schistosomes cDNAs. The expression profiles in different developmental stages were detected by real-time quantitative RT-PCR. The open reading frame (ORF) was subcloned into a pET28a(+) vector and transformed into BL21 and the recombinant protein was induced by IPTG. The immune characters of the purified recombinant protein were analyzed by Western blotting and immunoprotection in BALB/c mice. RESULTS: Bioinformatics analysis indicated that SjIM had an ORF of 834 base pairs that encoded 278 amino acids. Real-time quantitative RT-PCR analysis revealed that SjIM was upregulated in 35-day-old schistosomes, while the expression level in females was higher than that in male worms in 42nd day. Western blotting showed that the recombinant SjIM was immunogenic. An immunoprotection experiment in BALB/c mice showed that vaccination with recombinant SjIM could induce 48.76% and 41.29% reductions in the numbers of worms and eggs in the liver, respectively. CONCLUSIONS: The gene of SjIM is obtained from schistosomes cDNAs and the recombinant SjIM protein is induced successfully in E. coli. These aforementioned results demonstrate that the recombinant SjIM cand induce partial protection against schistosomiasis in BALB/c mice.

Inositol hexakisphosphate kinase 1 regulates neutrophil function in innate immunity by inhibiting phosphatidylinositol-(3,4,5)-trisphosphate signaling.

Inositol phosphates are widely produced throughout animal and plant tissues. Diphosphoinositol pentakisphosphate (InsP7) contains an energetic pyrophosphate bond. Here we demonstrate that disruption of inositol hexakisphosphate kinase 1 (InsP6K1), one of the three mammalian inositol hexakisphosphate kinases (InsP6Ks) that convert inositol hexakisphosphate (InsP6) to InsP7, conferred enhanced phosphatidylinositol-(3,4,5)-trisphosphate (PtdIns(3,4,5)P3)-mediated membrane translocation of the pleckstrin homology domain of the kinase Akt and thus augmented downstream PtdIns(3,4,5)P3 signaling in mouse neutrophils. Consequently, these neutrophils had greater phagocytic and bactericidal ability and amplified NADPH oxidase-mediated production of superoxide. These phenotypes were replicated in human primary neutrophils with pharmacologically inhibited InsP6Ks. In contrast, an increase in intracellular InsP7 blocked chemoattractant-elicited translocation of the pleckstrin homology domain to the membrane and substantially suppressed PtdIns(3,4,5)P3-mediated cellular events in neutrophils. Our findings establish a role for InsP7 in signal transduction and provide a mechanism for modulating PtdIns(3,4,5)P3 signaling in neutrophils.

Inositol 1,4,5-trisphosphate 3-kinase B controls survival and prevents anergy in B cells.

Inositol 1,4,5-trisphosphate 3-kinase B (or Itpkb) and inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4), its reaction product, play an important role in the control of B lymphocyte fate and function in vivo. In order to investigate the fine mechanisms of Itpkb and Ins(1,3,4,5)P4 action in B cells, we crossed Itpkb(-/-) mice with transgenic mice expressing a 3-83µÎ´ B cell receptor (BCR) specific for membrane-bound MHC-I H2-K(b) and H2-K(k) molecules. On a non-deleting H2-K(d) genetic background, we show that Itpkb is important for the control of Bim protein expression and B cell survival rather than for the control of B cell development from one stage to another. Analyses of cell surface markers expression, proapoptotic Bim protein expression, in vitro survival and in vivo turnover demonstrated that BCR transgenic Itpkb(-/-) B cells exhibit an anergic phenotype with the notable exception of their enhanced antigen-induced calcium signalling. On a deleting H2-K(b) genetic background, we show that Itpkb is not essential for BCR editing or negative selection. These data establish Itpkb as an important regulator of B cell survival and anergy in vivo.

Regulation of immune cell development through soluble inositol-1,3,4,5-tetrakisphosphate.

The membrane lipid phosphatidylinositol-3,4,5-trisphosphate (PtdInsP(3)) regulates membrane receptor signalling in many cells, including immunoreceptor signalling. Here, we review recent data that have indicated essential roles for the soluble PtdInsP(3) analogue inositol-1,3,4,5-tetrakisphosphate (InsP(4)) in T cell, B cell and neutrophil development and function. Decreased InsP(4) production in leukocytes causes immunodeficiency in mice and might contribute to inflammatory vasculitis in Kawasaki disease in humans. InsP(4)-producing kinases could therefore provide attractive drug targets for inflammatory and infectious diseases.

The link between insulin resistance and preeclampsia: new perspectives.

In preeclampsia, there is exacerbation of physiological changes associated with pregnancy such as insulin resistance, altered immune responses and inflammatory pathway activation. These exaggerated responses seen in preeclampsia are reminiscent of metabolic syndrome, and also are evident in gestational diabetes mellitus. The link between these phenomena is not clear but novel findings providing some insight have been reported recently. Inositol phosphoglycan P-type (P-IPG) in preeclampsia has been extensively investigated and increased production has been demonstrated. This molecule acts as a second messenger of insulin, enhances the metabolic effects of insulin and is associated with insulin resistance. This review article summarizes current evidence of the role of inositol phosphoglycans in the metabolic syndrome that occurs in preeclampsia, discussed in the light of modifications found in gestational diabetes mellitus and diabetes type 2 in pregnancy in humans and animal models. An increase in urinary release of P-IPG during pregnancy may herald the onset of preeclampsia. Further knowledge about the nature of the metabolic syndrome during preeclampsia and the degree of association between its components will help to inform future research efforts and to identify biochemical markers that could help in clinical practice, for example early markers that will have utility in managing disease progression.

Beyond IP3: roles for higher order inositol phosphates in immune cell signaling.

Nearly 25 years ago the first function of an inositol phosphate, namely Ins(1,4,5)P3, was reported to act as a "second messenger" to mobilize calcium from the endoplasmic reticulum (ER). Since this discovery, many other inositol phosphates and the kinases and phosphatases that generate these inositol phosphates have subsequently been discovered. However, the function of these "higher order" inositol phosphates in biological processes, if any, has remained a mystery. Interest in higher order inositol phosphates, such as Ins(1,3,4,5)P4, was renewed this year following reports of novel roles for these molecules in distinct processes within the immune system ranging from T cell development, B cell development and tolerance induction, as well as neutrophil and mast cell function. In this review, we will touch upon recent advances in inositol phosphate function in mammalian cells. More specifically, we will highlight new studies that have identified novel functions for specific higher order inositol phosphates, such as Ins(1,3,4,5)P4, in the immune system.

Preeclampsia, insulin signalling and immunological dysfunction: a fetal, maternal or placental disorder?

An inappropriate glycogen accumulation in preeclamptic placentas was described as secondary to biochemical alterations. Insulin resistance is widely accepted to be associated with preeclampsia, although its basis remain unclear. A family of putative insulin mediators, namely inositol phosphoglycans, were described to exert many insulin-like effects on lipid and glucose metabolism. A definite association between the P-type mediator (P-IPG) and preeclampsia was reported, being increased in placenta, urine, amniotic fluid and cord blood from human preeclamptic pregnancies. A strong link exists between insulin resistance and inflammation. Clear features of insulin resistance and systemic inflammatory activation were described in preeclampsia. It may be a consequence of the immunological dysfunction that occurs in preeclampsia that is temporized during sperm exposure and co-habitation which confuses the maternal immune network to perceive 'danger'. The over-expression of P-IPG during preeclampsia may be a counter-regulatory mechanism to insulin resistance since these molecules mimic insulin action. Besides, the lipidic form of P-IPG was reported to be similar to endotoxins, and may represent the 'danger signa'. We propose here a novel working theory on insulin resistance and preeclampsia.

Cross talk between T and B cells generates B antigen-presenting cells able to induce inositol phosphate production in T cells responding to Mls(a) superantigens.

Previous studies showed that activation of CD4+ T cells with mouse mammary tumor virus-encoded Mls(a) superantigens induces strong proliferative responses and interleukin-2 production but fails to elicit typical early T cell receptor (TCR)-mediated signal transduction events, such as hydrolysis of polyphosphoinositides (PI) or an increase in intracellular calcium. Here we show that the failure of Mls(a) antigen to activate PI hydrolysis applies when resting B cells are used as antigen-presenting cells (APC). By contrast, when Mls(a)-bearing B cells are activated for 24 h by exposure to lipopolysaccharide or, more importantly, to Mls(a)-reactive T cells or anti-CD40 antibodies the cells develop the capacity to elicit easily detectable PI turnover. These studies demonstrate that, for B cells as APC, the initiation of certain TCR-associated signal transduction pathways can depend on activation of the APC. The data suggest that cross talk between T cells and resting B cells can suffice to generate competent B APC and lead to the delayed initiation of signaling pathways important in T cell responses.

Inositol 1,3,4,5-tetrakisphosphate as a mediator of neuronal death in ischemic hippocampus.

Selective death of CA1 pyramidal neurons after transient forebrain ischemia has attracted interest for its possible relation to the pathogenesis of memory deficits and dementia. Using whole cell patch-clamp recording from CA1 pyramidal neurons in hippocampal slices of gerbils after ischemia we studied the intracellular signaling mechanisms related to the phosphoinositide cycle. Intracellular application of an antibody against phosphatidylinositol 4,5-bisphosphate rescued ischemic neurons from stimulus-induced irreversible depolarization. Furthermore, application of inositol 1,3,4,5-tetrakisphosphate in normal cells caused an irreversible depolarization in response to synaptic input, which mimicked the deterioration of ischemic neurons. Depolarization of both ischemic and normal neurons in the presence of inositol 1,3,4,5-tetrakisphosphate was prevented by the addition of the Ca2+ chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetate. Application of antibody against inositol 1,4,5-triphosphate 3-kinase, which blocks formation of inositol 1,3,4,5-tetrakisphosphate, also protected against cell deterioration. Our results suggest that the vulnerability of hippocampal pyramidal neurons following ischemia is caused by a disturbed phosphoinositide cascade, with one metabolite, inositol 1,3,4,5-tetrakisphosphate, playing a key role in the induction of Ca2+ accumulation, which leads to neuronal death.

Brain-derived neurotrophic factor and neurotrophin-3 support the survival and neuritogenesis response of developing cochleovestibular ganglion neurons.

The effects of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) on the differentiation of avian cochleovestibular ganglion and their possible association with the hydrolysis of glycosyl-phosphatidylinositol (GPI) were studied. BDNF and NT-3 (2 ng/ml) promoted neurite outgrowth in explants of both cochlear and vestibular ganglia. This effect on neuritogenesis was stage-dependent, reaching a maximum at E7 for NT-3 and at E9 for BDNF. The magnitude of the response of the vestibular ganglion to BDNF was always smaller than that of the cochlear ganglion of an equivalent stage. BDNF and NT-3 stimulation of neuronal survival and neurite extension was also demonstrated in dissociated neuronal cell cultures. The effect was concentration-dependent with saturation of the response occurring at 4 ng/ml for BDNF and at 2 ng/ml for NT-3, the half-maximal effect occurring at 2 and 1 ng/ml, respectively, for the most sensitive stages of the chick cochlear ganglion. Inositol phosphoglycan (IPG) did not mimic the effects of BDNF or NT-3 on neuronal survival and neurite outgrowth, nor was it able to potentiate their responses. Antibodies raised against IPG did not block the effects of these neurotrophins. The results suggest that BDNF and NT-3 may act in cooperation to establish the innervation pattern of the inner ear. Unlike their early proliferative effects, neurotrophic effects are uncoupled from the GPI/IPG signal transduction system.

Brain-derived neurotrophic factor and neurotrophin-3 induce cell proliferation in the cochleovestibular ganglion through a glycosyl-phosphatidylinositol signaling system.

We have investigated the role of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in the regulation of cell proliferation in the early developing cochleovestibular ganglion (CVG). Ganglia were isolated from 72-hr chick embryos and cultured for 24 hr. Both BDNF and NT-3 had a powerful mitogenic effect, at doses of 1-5 ng/ml, consistent with an involvement of the high-affinity receptor. Evidence for the participation of the glycosyl-phosphatidylinositol (GPI)/inositol phosphoglycan (IPG) signaling system in the mediation of proliferative effects of BDNF and NT-3 is presented. Both of these neurotrophins elicited a fast and transient hydrolysis of labeled GPI, approximately 60% in 30 sec. The dose-response profile of GPI hydrolysis overlaps the neurotrophin-induced cell proliferation response profile. Anti-IPG antibodies were able to block the growth-promoting effects of BDNF and NT-3. Anti-IPG antibodies immunoprecipitated a CVG-endogenous IPG, induced upon BDNF treatment, which exhibited proliferative stimulating properties. Both BDNF and NT-3 are proposed as potential candidates for regulation of growth during CVG development, with this mitogenic effect being mediated by the GPI/IPG signaling system.

Electrophysiological and biochemical evidence for bradykinin receptors on cultured rat cortical oligodendrocytes.

The effects of the neuropeptide bradykinin (Bk) were examined on antigenically-identified rat cortical oligodendrocytes. Bk significantly increased the incorporation of [3H]myo-inositol into phospholipids, indicating the turnover of phosphatidyl inositol (PI). Ca2+ flux analysis experiments confirmed that this effect was accompanied by an increase in intracellular Ca2+. Using the whole-cell patch clamp technique, Bk was shown to induce an inward current associated with a decrease in membrane conductance, indicating a closure of ion channels. The reversal potential of the current was close to the potassium equilibrium potential, consistent with an effect on a K+ conductance in these cells. These results show that oligodendrocytes possess Bk receptors that may be of functional relevance.

The involvement of inositol phosphoglycan mediators in the modulation of steroidogenesis by insulin and insulin-like growth factor-I.

We have investigated the mechanisms by which insulin and insulin-like growth factor-I (IGF-I) regulate the synthesis of progesterone by swine ovary granulosa cells. Analysis of the cell density dependence of the effects of insulin and IGF-I showed that the induction of progesterone synthesis by these growth factors is consistent with an autocrine or paracrine model of action, which involves the insulin- and IGF-I-stimulated release of a soluble factor(s) into the culture medium. We have tested the hypothesis that this soluble factor(s) may be structurally related to inositol phosphoglycans, a class of putative second messengers of the action of insulin. Consistent with this hypothesis, we isolated an activator of pyruvate dehydrogenase (PDH) phosphatase from culture medium obtained from cells treated with insulin or IGF-I. Further analysis showed that specific antibodies raised against the inositol phosphoglycan anchor of the variant surface glycoprotein of Trypanosoma brucei blocked the activation of PDH phosphatase by the material isolated from the culture medium, suggesting a close structural relationship between this putative PDH phosphatase activator and inositol phosphaglycans. Pertussis toxin treatment, shown to inhibit the generation of inositol phosphoglycans in other systems, was found to inhibit the effects of insulin on progesterone synthesis in granulosa cells. Finally, the stimulatory effects of insulin and IGF-I on progesterone synthesis by intact granulosa cells were markedly inhibited by the addition of antiinositol phosphoglycan antibodies to the culture medium. Based on these observations, we propose that the release of inositol phosphoglycans into the extracellular medium plays an important role in the signaling mechanisms by which insulin and IGF-I regulate the synthesis of progesterone in swine ovary granulosa cells.

Characterization of an antibody to the cross-reacting determinant of the glycosyl-phosphatidylinositol anchor of human membrane dipeptidase.

A polyclonal antiserum raised to the phospholipase C-solubilized form of membrane dipeptidase (EC 3.4.13.11) purified from human kidney was found to cross-react with unrelated trypanosomal and porcine glycosyl-phosphatidylinositol anchored proteins. Those antibodies recognising the cross-reacting determinant (CRD) were isolated by chromatography on a column of immobilized phospholipase C-solubilized porcine aminopeptidase P (EC 3.4.11.9), and the epitopes involved in the recognition were then characterized by immunoelectrophoretic blot analysis and by a competitive ELISA. The phospholipase C-solubilized forms of human and porcine membrane dipeptidase, porcine aminopeptidase P and trypanosome variant surface glycoprotein were recognised by the anti-CRD antiserum, and this recognition was abolished by prior treatment of the proteins with either mild acid or nitrous acid. In contrast, the detergent-solubilized, membrane-forms of human and porcine membrane dipeptidase were not recognised. Of a range of components of the glycosyl-phosphatidylinositol anchor, only inositol 1,2-cyclic monophosphate and the insulin-mimetic disaccharide, glucosaminyl-1,6-inositol 1,2-cyclic monophosphate, inhibited in the micromolar range the binding of the anti-CRD antiserum to immobilized porcine aminopeptidase P. These results indicate that the major epitope recognised by this anti-CRD antiserum is the inositol 1,2-cyclic monophosphate formed on phospholipase C cleavage of the glycosyl-phosphatidylinositol anchor.

Antibodies against phosphatidylinositol and inositol monophosphate specifically inhibit tumour necrosis factor induction by malaria exoantigens.

The active component of the exoantigens of malarial parasites which stimulates macrophages to secrete tumour necrosis factor (TNF) has been shown to depend upon a phospholipid, the activity of which was blocked by phosphatidylinositol (PI) and inositol monophosphate (IMP) in competitive inhibition studies. Antisera made against the exoantigens of Plasmodium yoelii, which inhibited their induction of TNF, were found by an ELISA assay to contain antibody against several other phospholipids. However, the inhibitory antibody was removed specifically by adsorption with liposomes containing PI, but not other phospholipids. Furthermore, PI was the only phospholipid in non-liposomal form which induced the production of inhibitory antisera. Mice immunized with IMP, but not inositol, also produced inhibitory antisera. When incorporated into liposomes several other phospholipids did give rise to inhibitory antibodies but, in contrast to the antisera against parasite exoantigens, PI and IMP, the inhibitory activity was removed by adsorption with heterologous phospholipid liposomes, suggesting that it was directed against a common determinant, presumably the phosphate ester head group. Inhibitory antibodies in the antisera tested were predominantly IgM and titres were not increased after repeated injections. Antisera raised against PI, IMP or the cross-reacting phospholipid liposomes also inhibited TNF secretion by macrophages stimulated by exoantigens of the human parasites P. falciparum and P. vivax, but not by bacterial lipopolysaccharide. These findings confirm our conclusion that exoantigens from these different species contain phosphate bound to inositol in their TNF-inducing moiety.

The effect of a cAMP analogue on Ca2+ ionophore-, antigen- and agonist-induced inositol phosphate release in rat basophilic leukaemia (RBL-1) cells.

The effect of the stable cAMP analogue 8-Br-cAMP on leukotriene D4 (LTD4)-, 5'-N-ethyl-carboxamidoadenosine (NECA)-, antigen- and Ca2+ ionophore-induced inositol phosphate (IP) production was studied in RBL-1 cells. The cAMP analogue significantly inhibited LTD4- and antigen induced-IP production, thus supporting the hypothesis of a negative interaction between cAMP and phosphoinositide breakdown in blood cells. Ionophore-induced IP release, which was blocked by a 5-lipoxygenase inhibitor and by a LT-receptor antagonist, and therefore is probably mediated by LTs, was also inhibited by 8-Br-cAMP. NECA-induced IP release was not significantly inhibited by the cyclic nucleotide, thus showing that the effect described herein is not a general action on receptor-activated phospholipase C. 8-Br-cAMP did, however, inhibit GTP gamma S-induced IP release in permeabilised RBL-1 cells, thus suggesting that the inhibition does not occur at the receptor level but might be due, at least in part, to an effect on some receptor-coupled G proteins.