Establishment of the cells useful for murine interleukin-18 bioassay by introducing murine interleukin-18 receptor cDNA into human myelomonocytic KG-1 cells

The -137G/C Polymorphism in Interleukin-18 Gene Promoter Contributes to Chronic Lymphocytic and Chronic Myelogenous Leukemia Risk in Turkish Patients

Objective:

Interleukin-18 (IL-18) is a cytokine that belongs to the IL-1 superfamily and is secreted by various immune and nonimmune cells. Evidence has shown that IL-18 has both anticancer and procancer effects. The aim of this study was to evaluate the relationship between IL-18 gene polymorphisms and susceptibility to chronic lymphocytic leukemias (CLL) and chronic myelogenous leukemias (CML) in Turkish patients.

Materials and Methods:

The frequencies of polymorphisms (rs61667799(G/T), rs5744227(C/G), rs5744228(A/G), and rs187238(G/C)) were studied in 20 CLL patients, 30 CML patients, and 30 healthy individuals. The genotyping was performed by polymerase chain reaction and DNA sequencing analysis.

Results:

Significant associations were detected between the IL-18 rs187238(G/C) polymorphism and chronic leukemia. A higher prevalence of the C allele was found in CML cases with respect to controls. The GC heterozygous and CC homozygous genotypes were associated with risk of CML when compared with controls. However, prevalence of the C allele was not significantly high in CLL cases with respect to controls. There was only a significant difference between the homozygous CC genotype of CLL patients and the control group; thus, it can be concluded that the CC genotype may be associated with the risk of CLL. Based on our data, there were no significant associations between the IL-18 rs61667799(G/T), rs5744227(C/G), or rs5744228(A/G) polymorphisms and CLL or CML.

Conclusions:

IL-18 gene promoter rs187238(G/C) polymorphism is associated with chronic leukemia in the Turkish population. However, due to the limited number of studied patients, these are preliminary results that show the association between -137G/C polymorphism and patients (CLL and CML). Further large-scale studies combined with haplotype and expression analysis are required to validate the current findings.

Measurement of human and mouse interleukin 18

IL-18, originally designated as interferon-gamma (IFN-gamma)-inducing factor (IGIF), is a pleiotropic cytokine secreted by activated macrophages and Kupffer cells. The major activity associated with this cytokine is induction of IFN-gamma production from T cells, B cells, and NK cells, especially in collaboration with IL-12. IL-18 is synthesized without a signal peptide and must be enzymatically cleaved to become active. Therefore, it is important to determine whether the produced IL-18 is an active or precursor form. This unit describes functional assays for measurement of bioactive human and mouse IL-18 and ELISAs for measurement of murine and human IL-18 proteins. The functional assays are based on the induction of IFN-gamma production by IL-18. The ELISA measures the concentration of human or mouse IL-18. Using a combination of monoclonal antibodies against human or mouse IL-18, the proform and/or mature form of IL-18 can be detected by ELISA.

Murine CTLL-2 cells respond to mIL12: prospects for developing an alternative bioassay for measurement of murine cytokines IL12 and IL18

Cell line-based bioassays are becoming increasingly popular for assessment of biological activities of cytokines primarily because these are easy to perform and are not subject to donor variation. A well characterised cell line with world wide availability would further minimise the inter-assay variations. C57BL/6 mice derived T cell line; CTLL-2 fits this criterion. We explored the potential of CTLL-2 cells to develop a bioassay to detection of murine (m) IL12 and mIL18. Both cytokines have shown significant activity against a number of cancers and importantly, act synergistically via mutual upregulation of each other's receptors. The preliminary flow cytometric analyses of immunostained CTLL-2 cells showed that approximately 65% expressed mIL12 and approximately 5% expressed mIL18 receptors suggesting that these may respond to mIL12. As predicted, cells incubated with different doses of mIL12 or mIL18 for 72 h were responsive to mIL12 and not to mIL18. However, when pre-treated with mIL12 for 24 h prior to incubation with mIL18, there was a significant enhancement in response. The sensitivity of the response was comparable to that obtained using the conventional splenocyte-based IFNgamma release assay. The cytokine specificity of the response was proven unequivocally when significant reduction in CTLL-2 response was observed in the presence of the relevant neutralising antibodies. Finally, we could successfully detect lowest doses of approximately 0.1 pg/microL mIL12 or 40 pg/mL of mIL18 in cell supernatants in a cytokine specific manner, which is lower than the resting levels of these cytokines in mouse sera. Again the sensitivity was comparable to that observed in the conventional IFNgamma release assay. Hence, we have demonstrated the potential of CTLL-2-based bioassay to detect biologically active mIL12 and mIL18 in biological samples accurately and reproducibly.

The Effect of AgK114 on Wound Healing

AgK114 is a newly isolated membrane-associated protein which is expressed on keratinocytes. Its expression is restricted to dermal sheath cells near sebaceous glands in normal skin. However, it is transiently induced by UV exposure or injury stimulation (Tatefuji T. et al., Biol. Pharm. Bull., 27, 1742-1749, 2004). Thus, the expression pattern of AgK114 suggested its potential role in wound healing response. We report here that expression of AgK114 is induced in the initial 24 h at the edge keratinocytes during keratinocyte migration, followed by disappearance once epithelialization is completed in the murine excisional wound model. We also demonstrate that exogenous recombinant mouse AgK114FL promoted wound healing process. Mouse AgK114FL up-regulated pro-matrix-metalloproteinase-9, vascular endothelial growth factor, transforming growth factor-beta, IL-6, and IL-1beta production in the early stage of wound tissue. Moreover, mouse AgK114FL induced the matrix-metalloproteinase-9 activity of wound fibroblasts prepared from impaired skin in the presence of proinflammatory cytokines. These results suggest that the AgK114 participates in the wound response during the healing process, and promotes wound repair.

Nitric oxide inducing function and intracellular movement of chicken interleukin-18 in cultured cells

To evaluate the characteristics of chicken interleukin-18 (ChIL-18) in different forms in vitro, the ChIL-18 full-length gene (ChIL-18-F) and the ChIL-18 presumed mature protein gene (ChIL-18-M) were cloned and inserted into the eukaryotic expression vector pCI, to construct recombinant pCI-ChIL-18-F and pCI-ChIL-18-M. The recombinant plasmids were then transferred into chicken splenic lymphocytes (CSLs). Western blot showed that ChIL-18-F, with a molecular weight of 23.0 kDa, was produced in CSLs transfected by pCI-ChIL-18-F; ChIL-18-M, with a molecular weight of 19.5 kDa, was produced in CSLs transfected by pCI-ChIL-18-M. The nitric oxide (NO) level in the transfected CSLs and the culture medium at different time points was further examined under confocal microscopy using 4,5-diaminofluorescein staining. The results showed that both pCI-ChIL-18-F and pCI-ChIL-18-M groups showed significant increase in intracellular and extracellular NO production compared with pCI transfected control cells. These results suggest that both ChIL-18-F and ChIL-18-M could stimulate NO secretion in CSLs. To characterize the intracellular distribution of ChIL-18, ChIL-18-F and ChIL-18-M were each fused to the enhanced green fluorescent protein gene, and expressed in Vero cells. The results showed that the ChIL-18-F tended to the membranous region in Vero cells, while ChIL-18-M did not. This indicates that the N-terminal 27 amino acid peptide helped ChIL-18 target to Vero cell membranes.

The protective role of interleukin-18 in Salmonella infection

Since its derivation, much has been learned about the proinflammatory inducing cytokine interleukin-18, and its role in resolving infectious diseases. Studies to date that examined interleukin-18 have shown that endogenously induced interleukin-18 plays an important protective role in some viral and bacterial infections. However, interleukin-18 has a limited role in protective immunity to Salmonella infections, and is secondary to the protective role of interleukin-12. This lack of sensitivity to interleukin-18 may be in part related to the dependence on interleukin-12 for interleukin-18 receptor expression and to the nanomolar concentrations that are required. Nonetheless, an understanding of how some pathogens have evolved to circumvent interleukin-18 and of how interleukin-18 can be effectively induced are essential to our ability to develop better vaccines against enteric pathogens.

Expression and responsiveness of human interleukin-18 receptor (IL-18R) on hematopoietic cell lines

Interleukin-18 (IL-18) is a new inflammatory cytokine sharing biological functions with IL-12. The human IL-18 receptor (IL-18R) was recently identified and was found to be expressed on normal peripheral blood lymphocytes. To further characterize IL-18R, we analyzed IL-18R expression using a series of human hematopoietic cell lines selected from various cell lineages. We found the IL-18R expression on cells of T and B lineages as expected from analysis on normal cells. The IL-18R expression, however, was found not to be restricted to any specific maturation stages of T and B cells. In addition, we detected IL-18R expression in myeloid, monocytoid, erythroid and megakaryocytic cell lines, indicating that normal counterparts of these cell lineages could express IL-18R and participate in in vivo reactions caused by IL-18. Biochemical studies showed that IL-18R proteins exist as heterogeneous molecules ranging from 60 to 110 kDa. Deglycosylation experiments indicated that the heterogeneity could not be explained only by a difference in glycosylation. We also found that tumor necrosis factor-alpha (TNF-alpha) modulated the IL-18R expression, which implies an important in vivo effect of TNF-alpha on IL-18-induced reaction. Analyzing the responsiveness of IL-18R, we found that only KG-1 responded to IL-18 stimulation. This suggests that certain inhibitory mechanisms of IL-18 responsive genes are involved in the all IL-18R-positive cell lines except KG-1.

IL-18 binding and inhibition of interferon gamma induction by human poxvirus-encoded proteins

Molluscum contagiosum virus (MCV) is a common, human poxvirus that causes small papular skin lesions that persist for long periods without signs of inflammation. Previous studies revealed that MCV encodes a family of proteins with homology to mammalian IL-18 binding proteins. IL-18 is a proinflammatory cytokine that induces synthesis of interferon gamma, activates NK cells, and is required for a T-lymphocyte helper type 1 response. We expressed and purified the proteins encoded by the MC53L and MC54L genes of MCV, as well as their human and murine homologs. All four recombinant proteins were able to bind with high affinity to human and murine IL-18 molecules and inhibited IL-18 mediated interferon gamma production in a dose-dependent manner. The pirating of IL-18 binding proteins by poxviruses and their use as decoy receptors is consistent with the critical role of IL-18 in defense against virus infections and provides a mechanism for evasion of the immune system by MCV.