Targeting interleukin 18 with interleukin 18 binding protein

A novel, constitutively expressed and secreted interleukin 18 (IL18) binding protein (IL18BP) neutralises IL18. IL18BP shares many characteristics with soluble cytokine receptors of the IL1 family in that the protein exhibits specificity for IL18, belongs to the immunoglobulin-like class of receptors and has limited amino acid sequences with those of the IL1 receptor type II. However, unlike soluble cytokine receptors, IL18BP does not have a transmembrane domain and hence is not anchored to the cell membrane. IL18BP is a secreted protein and not cleaved from the cell surface. IL18BP is naturally occurring and was isolated from the urine of healthy subjects. Because IL18 is an important inducer of interferon gamma (IFNgamma), IL18BP suppresses the production of IFNgamma resulting in reduced T-helper type 1 immune responses. There are four human and two mouse isoforms-resulting from mRNA splicing and found in various cDNA libraries. Each of these IL18BP isoforms have been expressed, purified and assessed for binding and neutralisation of IL18 biological activities. Two human IL18BP isoforms exhibited the greatest affinity for IL18 with a rapid on-rate, a slow off-rate and a dissociation constant (kDa) of 399 pM. The two other isoforms with an incomplete immunoglobulin domain were unable to neutralise IL18. The two human isoforms that possess a complete immunoglobulin domain, neutralise >95% IL18 at a molar excess of two. Molecular modelling identified a large mixed electrostatic and hydrophobic binding site in the immunoglobulin domain of IL18BP, which could account for its high affinity binding to the ligand. These high affinity forms may be ideally suited for blocking IL18 in human disease. It is likely that preferential secretion of high affinity functional and non-functional isoforms of IL18BP affect the immune response and the outcome of disease.     

Serum interleukin 18 and interleukin 18 binding protein in rheumatoid arthritis

OBJECTIVE: To measure serum interleukin 18 (IL18) and IL18 binding protein (IL18BP) levels in patients with inflammatory arthropathies, and to identify associations with disease status and the response to treatment. METHODS: Serum samples were obtained before and after methotrexate treatment from patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA) attending an early arthritis clinic. IL18 and IL18BP were measured by enzyme linked immunosorbent assay (ELISA). RESULTS: Sixty patients with RA and 13 with PsA were evaluated. Serum IL18 levels were significantly higher in RA than in PsA (p<0.001). After six months' treatment with methotrexate, IL18 levels were reduced, but the differences were not significant (p=0.052). In cross sectional analyses, no correlations between IL18 levels and measures of disease activity or structural damage in RA were found. In longitudinal analyses, no correlations between IL18 levels and the response to treatment or the degree of progressive joint damage were found. Similarly, IL18BP levels were raised in RA, and were not associated with measures of the clinical status or the response to treatment. CONCLUSION: Raised serum levels of IL18 are consistent with a pathophysiological role in RA. However, in this study measurement of circulating IL18 and IL18BP did not correlate significantly with clinical measures of disease activity or the response to treatment in patients with early RA.     

Evaluation of thoracic tumors with 18F-fluorothymidine and 18F-fluorodeoxyglucose-positron emission tomography

STUDY OBJECTIVES: 18F-fluorodeoxyglucose (FDG) is the most widely used positron emission tomography (PET) imaging probe used for the diagnosis, staging, restaging, and monitoring therapy response of cancer. However, its specificity is less than ideal. A new molecular imaging probe (18F-deoxyfluorothymidine [FLT]) has been developed that might afford more specific tumor imaging. The aims of this study were as follows: (1) to compare the use of FDG-PET and FLT-PET for tumor staging, (2) to compare the degree of FDG and FLT uptake in lung lesions, and (3) to determine the correlation between PET uptake intensity and tumor cell proliferation. DESIGN: FDG-PET and FLT-PET scans were performed in 11 patients with solitary pulmonary nodules and another 11 patients with known non-small cell lung cancer (NSCLC). Tracer uptake was assessed quantitatively by standardized uptake values (SUVs). Histologic evaluation of tissue samples obtained from biopsy specimens or surgical resections served as the "gold standard." Tumor cell proliferation was assessed by Ki-67 staining. RESULTS: Pathology verification was available from 99 tissue samples in the 22 patients (29 pulmonary lesions, 66 lymph node stations, and 4 extrapulmonary lesions). Thirty-three samples (33.3%) were positive for tumor tissue (22 pulmonary, 9 lymph node stations, and 2 extrapulmonary). FDG-PET findings were false-positive in three pulmonary lesions, while FLT-PET findings were false-positive in one lesion. There were two false-negative findings by FDG-PET and six false-negative findings by FLT-PET. FDG uptake of the malignant lesions was significantly higher than FLT (maximum SUV, 3.1 +/- 2.6 vs 1.6 +/- 1.2 [mean +/- SD]; p < 0.05). A significant correlation was observed between FLT uptake of pulmonary lesions and Ki-67 labeling index (r = 0.60, p = 0.02) but not for FDG uptake (r = 0.27, p = not significant). CONCLUSIONS: Compared to FDG-PET, detection of primary and metastatic NSCLC by FLT-PET is limited by the relatively low FLT uptake of the tumor tissue. Thus, FLT-PET is unlikely to provide more accurate staging information or better characterization of pulmonary nodules than FDG-PET. Nevertheless, the correlation between FLT uptake and cellular proliferation suggests that future studies should evaluate the use of FLT-PET for monitoring treatment with cytostatic anticancer drugs.     

Interleukin 18 and interleukin 18 binding protein in patients with idiopathic thrombocytopenic purpura

To evaluate the balance of interleukin IL18 and its endogenous antagonist IL18 binding protein ( IL18BP ) in patients with idiopathic thrombocytopenic purpura (ITP), plasma IL18 , IL18BP , interferon gamma ( IFNG ) and IL4 levels, as well as platelet counts were measured in patients with active ITP ( n  = 23), ITP in remission ( n  = 21) and in healthy subjects ( n  = 24) by enzyme linked immunosorbent assay (ELISA). Using real-time quantitative polymerase chain reaction, the mRNA expression of IL18 , IL18BP , IFNG , IL4 , T-box ( TBX21 ) and GATA-binding protein 3( GATA3 ) were studied in all subjects. The results showed that IL18 and IFNG protein and mRNA levels were significantly increased in patients with active ITP than in control subjects, but that IL18BP were not significantly elevated in ITP patients, which resulted in an elevated ratio of IL18/IL18BP in patients with active disease. During remission stages, the levels of these cytokines were comparable to those of healthy controls. The elevated levels of IL18/IL18BP in plasma during active stages of disease suggest a possible role in the pathogenesis and course of ITP.