Aged interleukin-10tm1Cgn chronically inflamed mice have substantially reduced fat mass, metabolic rate, and adipokines

Interleukin 10tm1Cgn (IL 10tm) mice have been utilized as a model of chronic inflammation and declining health span because of their propensity to develop chronic activation in NFkB pathways, skeletal muscle and cardiac changes, and mitochondrial dysfunction. We hypothesized that older IL 10tm frail mice would have alterations similar to frail, older humans in measured parameters of glucose metabolism, oxygen consumption (VO2), respiratory quotient (RQ), spontaneous locomotor activity, body composition and plasma adipokine levels. To test this hypothesis, we investigated these metabolic parameters in cohorts of 3, 10, and 20 month old IL 10tm female mice and age and gender matched C57Bl/6 mice. Insulin sensitivity, glucose homeostasis, locomotor activity and RQ were not significantly altered between the two strains of mice. Interestingly, old IL 10tm mice had significantly decreased VO2 when normalized by lean mass, but not when normalized by fat mass or the lean/fat mass ratio. NMR based body composition analysis and dissection weights show that fat mass is decreased with age in IL 10tm mice compared to controls. Further, plasma adiponectin and leptin were also decreased in IL 10tm.These findings suggest that frailty observed in this mouse model of chronic inflammation may in part be driven by alterations in fat mass, hormone secretion and energy metabolism.

Src homology 2 domain-containing inositol 5' phosphatase is negatively associated with histamine release to human recombinant histamine-releasing factor in human basophils

BACKGROUND

The human recombinant histamine-releasing factor (HrHRF) acts as a complete stimulus for histamine release and IL-4 secretion from a subpopulation of highly allergic donor basophils, termed IgE(+) basophils. Additionally, IgE(+) basophils release histamine to other secretogues, IL-3, and deuterium oxide. We hypothesized that IgE(+) basophils were hyperreleasable.

OBJECTIVE

Deficiencies in early signal transduction events associated with Fc(epsilon)RI lead to a nonreleasable phenotype, whereas the Src homology 2 domain--containing inositol 5' phosphatase (SHIP) knockout mice have hyperreleasable mast cells. The purpose of this study was to ascertain whether a difference in intracellular signaling molecules could explain the hyperreleasable phenotype of human IgE(+) basophils.

METHODS

Basophils were purified by means of double Percoll gradients and negative selection with magnetic beads. Cell lysates were Western blotted for the tyrosine kinases Lyn and Syk and the phosphatase SHIP. Additionally, histamine release to HrHRF was performed in addition to real-time RT-PCR to investigate mRNA for SHIP.

RESULTS

We show a striking negative correlation between the amount of SHIP protein per cell equivalent, but not Lyn or Syk, and maximum histamine release to HrHRF. This deficiency of SHIP was observed in basophils, but not lymphocytes or monocytes, of these IgE(+) donors. Additionally, levels of mRNA for SHIP did not differ between IgE(+) and IgE(-) donor basophils, which is consistent with a posttranscriptional mechanism of protein regulation. SHIP and phosphatidylinositol 3-kinase reciprocally regulate phosphatidylinositol (3,4,5) triphosphate levels. We also demonstrated that Ly294002, the phosphatidylinositol 3 kinase inhibitor, prevented HrHRF-induced histamine release in IgE(+) donor basophils.

CONCLUSION

Taken together, these data suggest that the hyperreleasability of IgE(+) donors is associated with low levels of SHIP and implicate SHIP as an additional regulator of secretion in human basophils.

Immune mimicry in malaria: Plasmodium falciparum secretes a functional histamine-releasing factor homolog in vitro and in vivo

The Plasmodium falciparum translationally controlled tumor protein (TCTP) is a homolog of the mammalian histamine-releasing factor (HRF), which causes histamine release from human basophils and IL-8 secretion from eosinophils. Histamine, IL-8, and eosinophils have been reported to be elevated in patients with malaria. This study was undertaken to determine whether malarial TCTP is found in the plasma of malaria-infected patients and to determine whether it has HRF biologic activity. Malarial TCTP was found in lightly infected human volunteers and in heavily infected Malawian children, but not in uninfected patients. Recombinant malarial TCTP, like HRF, stimulated histamine release from basophils and IL-8 secretion from eosinophils in vitro. Whereas malarial TCTP was less active than HRF, the concentrations that were effective in vitro could be achievable in vivo. These data suggest that malarial TCTP, present in human plasma during a malarial illness, may affect host immune responses in vivo.

Human recombinant histamine-releasing factor activates human eosinophils and the eosinophilic cell line, AML14-3D10

The human recombinant histamine-releasing factor (HrHRF) was previously shown to induce histamine release from human basophils from a subset of donors. The ability of HrHRF to directly induce histamine release from only certain basophils was thought to involve interaction between HrHRF and a particular kind of IgE, termed IgE(+), on the surface of these cells. Recent studies disproved the hypothesis that the IgE molecule or its high-affinity receptor, FcepsilonRI, is involved in secretion of histamine and cytokines by basophils stimulated with HrHRF. Rather, data suggest that HrHRF is a cytokine that stimulates basophils by binding to a cell-surface structure other than the IgE molecule. This report describes the effects of HrHRF on another inflammatory cell type: eosinophils from mildly allergic donors. In purified eosinophils primed with granulocyte-macrophage colony-stimulating factor, both tumor necrosis factor alpha (TNF-alpha) and HrHRF induced increased secretion of interleukin (IL) 8. In addition, both HrHRF and IL-5 enhanced secretion of IL-8 stimulated by TNF-alpha. Secretion of IL-8 reached a plateau level in less than 24 hours, was inhibited by cycloheximide, and required the presence of HrHRF throughout the culture period. In some eosinophil preparations, HrHRF induced calcium mobilization that was inhibited by pertussis toxin. Additionally, HrHRF caused secretion of IL-8 from the human eosinophilic cell line, AML14-3D10, which does not possess the alpha chain of FcepsilonRI. These data provide evidence that HrHRF contributes to activation of eosinophils and thus suggest an additional role for HrHRF in the pathophysiologic mechanisms of allergic disease.

Pharmacologic regulation of histamine release by the human recombinant histamine-releasing factor

BACKGROUND

The recently cloned human recombinant IgE-dependent histamine releasing factor (HrHRF) was initially thought to stimulate histamine release from human basophils from a subpopulation of allergic donors by interacting with the IgE molecules on the surface of these cells. Additional data suggest that HrHRF exerts its biologic effects by binding to a distinct cell surface structure and not to IgE.

OBJECTIVE

To address the hypothesis that the HrHRF signaling pathway is distinct from the classical high-affinity IgE receptor (FcepsilonRI) pathway, we used pharmacologic agents known to affect basophil histamine release.

METHODS

In this report we compared the effect of staurosporine, Bis II, Gö 6976, rottlerin, and pertussis toxin on histamine release from human basophils mediated by the following stimuli: HrHRF, polyclonal human anti-IgE antibody, and antigen, as well as the IgE-independent stimulus, FMLP.

RESULTS

None of these modulators, except rottlerin, could differentiate histamine release induced by anti-IgE or antigen from that induced by HrHRF. Rottlerin enhanced HrHRF-mediated histamine release and dose dependently blocked FMLP-mediated release without affecting basophil activation by either anti-IgE or antigen.

CONCLUSION

These data suggest a unique signaling pathway for HrHRF and thus strengthen the hypothesis that HrHRF binds to a specific receptor other than IgE.

The human recombinant histamine releasing factor: functional evidence that it does not bind to the IgE molecule

BACKGROUND

We have previously shown that the human recombinant histamine releasing factor (HrHRF) caused histamine release from a subset of basophils from donors with allergy, and this release seemed to be dependent on the presence of a certain type of IgE, termed IgE+. IgE molecules that did not support HrHRF-induced histamine release were termed IgE-. However, subsequently we demonstrated that HrHRF primes anti-IgE-antibody-induced histamine release from all basophils, irrespective of the type of IgE on the cell surface.

OBJECTIVE

Because these data suggested that HrHRF does not exert its biologic effects by binding to IgE, but rather that it interacted with a surface receptor on the basophil, we wanted to obtain functional evidence that HrHRF did or did not bind to the IgE molecule.

METHODS

The rat basophilic leukemia cell line (RBL-SX38), which has been transfected to express a functional human FcepsilonRI (alpha-, beta-, and gamma-chains of the receptor) in addition to the normal rat FcepsilonRI, was used. The presence of the human FcepsilonRI receptor enables these cells to be sensitized with human IgE. Cells were passively sensitized with 1000 ng/mL human IgE+ or 1000 ng/mL human IgE- for 60 minutes at 37 degrees C. Unsensitized cells served as a control. After the cells were washed, 1 x l0(5) cells were stimulated in the presence of 1 mmol/L Ca2+ with 0.1 microg/mL anti-IgE, 40 microg/mL HrHRF, or 40 microg/mL mouse recombinant HRF (MrHRF), which has 96% homology to HrHRF.

RESULTS

Mean anti-IgE-induced histamine release was 33% +/- 15%, and there was no difference between IgE+ sensitization (32% +/- 12%) and IgE- sensitization (34% +/- 18%). However, in contrast to human basophil experiments, neither HrHRF (0% +/- 0%) nor MrHRF (3% +/- 5%) caused histamine release in RBL cells sensitized with IgE+. In addition, priming the transfected RBL-SX38 cells or the parental cell line, RBL-2H3 cells, with HrHRF or MrHRF did not increase anti-IgE-induced histamine release.

CONCLUSION

The results indicate that HrHRF does not bind to IgE, either IgE+ or IgE-. Therefore it appears likely that rHRF signals through its own specific receptor, which is not expressed or functional on RBL-SX38 or RBL-2H3 cells, but which seems to be expressed on basophils of atopic and nonatopic donors.

IgE-dependent histamine-releasing factors. A brief review

A cytokine, termed histamine-releasing factor (HRF) and produced by many cell types, has become the focus of research by many investigators due to its potential importance as a stimulus in chronic inflammation. We are producing and characterizing an HRF which causes IgE-mediated histamine release from human basophils. Following extensive purification procedures, the molecule will be sequenced and synthesized. A functional heterogeneity of IgE molecules was revealed by these studies. We are currently producing IgE antibody in vitro and testing the hypothesis that differential glycosylation is the basis for the heterogeneity. Knowledge of the structures and interactions of these molecules should advance our understanding of allergic and more chronic diseases.