The effects of genetic polymorphisms of IL-6, IL-8, and IL-10 on Helicobacter pylori-induced gastroduodenal diseases in Korea

A meta-analysis of interleukin-10 -592 promoter polymorphism associated with gastric cancer risk

We aimed to explore the role of IL-10 -592 A/C SNP in the susceptibility to gastric cancer through a systematic review and meta-analysis. Each initially included article was scored for quality appraisal. 17 studies were eligible for the meta-analysis. We adopted the most probably appropriate genetic model (recessive model). Potential sources of heterogeneity were sought out via subgroup and sensitivity analyses, and publication biases were estimated. IL-10-592 AA genotype is associated with the reduced risk of developing gastric cancer among Asians and even apparently observed among Asians high quality subgroup, suggesting IL-10-592 AA genotype may seem to be more protective from overall gastric cancer in Asian populations. IL-10-592 AA genotype is also associated with the overall reduced gastric cancer susceptibility in persons with H. pylori infection compared with controls without H. pylori infection, suggesting IL-10-592 AA genotype may seem to be more protective from overall gastric cancer susceptibility in persons infected with H. pylori. IL-10-592 AA genotype is not associated with either pathologic subtypes (intestinal or diffuse) or anatomic subtypes (non-cardia or cardia) of gastric cancer susceptibility. Genotyping methods like direct sequencing should be highly advocated to be conducted in future well-designed high quality studies among different ethnicities or populations.

Associations between interleukin-6 gene -174 C/G and -572 C/G polymorphisms and the risk of gastric cancer: a meta-analysis

BACKGROUND AND OBJECTIVES

Epidemiological studies have evaluated the associations between interleukin-6 (IL-6) gene -174 C/G (rs1800795) and -572 C/G (rs1800796) polymorphisms and gastric cancer (GC) risk, but results and conclusions remain controversial. In order to derive a more precise estimation of the associations, we performed this meta-analysis.

METHODS

A meta-analysis was conducted to estimate the associations between IL-6 gene -174 C/G and -572 C/G polymorphisms and GC risk.

RESULTS

Nine articles involving 13 studies were included in the final meta-analysis, covering a total of 1,581 GC cases and 2,563 controls. For IL-6 gene -174 C/G polymorphism, nine studies were combined showing no evidence for associations between IL-6 gene -174 C/G polymorphism and GC risk. For IL-6 gene -572 C/G polymorphism, four studies were combined. There was also lack of evidence for significant association between IL-6 gene -572 C/G polymorphism and GC risk. In addition, the similar results were obtained in the subgroup analyses and cumulative meta-analysis.

CONCLUSIONS

The present meta-analysis suggests that IL-6 gene -174 C/G and -572 C/G polymorphisms are not associated with GC risk. However, due to the small subjects included in analysis and the selection bias in some studies, the results should be interpreted with caution.

Disease severity in patients infected with Leishmania mexicana relates to IL-1β

Leishmania mexicana can cause both localized (LCL) and diffuse (DCL) cutaneous leishmaniasis, yet little is known about factors regulating disease severity in these patients. We analyzed if the disease was associated with single nucleotide polymorphisms (SNPs) in IL-1β (−511), CXCL8 (−251) and/or the inhibitor IL-1RA (+2018) in 58 Mexican mestizo patients with LCL, 6 with DCL and 123 control cases. Additionally, we analyzed the in vitro production of IL-1β by monocytes, the expression of this cytokine in sera of these patients, as well as the tissue distribution of IL-1β and the number of parasites in lesions of LCL and DCL patients. Our results show a significant difference in the distribution of IL-1β (−511 C/T) genotypes between patients and controls (heterozygous OR), with respect to the reference group CC, which was estimated with a value of 3.23, 95% CI = (1.2, 8.7) and p-value = 0.0167), indicating that IL-1β (−511 C/T) represents a variable influencing the risk to develop the disease in patients infected with Leishmania mexicana. Additionally, an increased in vitro production of IL-1β by monocytes and an increased serum expression of the cytokine correlated with the severity of the disease, since it was significantly higher in DCL patients heavily infected with Leishmania mexicana. The distribution of IL-1β in lesions also varied according to the number of parasites harbored in the tissues: in heavily infected LCL patients and in all DCL patients, the cytokine was scattered diffusely throughout the lesion. In contrast, in LCL patients with lower numbers of parasites in the lesions, IL-1β was confined to the cells. These data suggest that IL-1β possibly is a key player determining the severity of the disease in DCL patients. The analysis of polymorphisms in CXCL8 and IL-1RA showed no differences between patients with different disease severities or between patients and controls.

Leishmania mexicana is an intracellular parasite that causes two polarly opposed diseases: One is a self-limited disease, characterized by ulcerative lesions associated with a low infectious load, as found in patients with localized cutaneous leishmaniasis (LCL). And the other pole is characterized by a progressive disease where abundant parasites spread uncontrollably throughout the skin inside heavily infected phagocytic cells, as occurs in patients with diffuse cutaneous leishmaniasis (DCL). The cause of this severe form of the disease is unknown, although the early encounter between the parasite and the inflammatory response of the host possibly plays a decisive role in the disease outcome. We here show that polymorphism in the gene encoding IL-1β (−511 C/T) represents a variable influencing the risk to develop the disease for patients infected with Leishmania mexicana. In vitro experiments showed that monocytes of DCL patients secreted significantly higher levels of the proinflammatory cytokine IL-1β as compared to LCL patients. DCL patients also had augmented levels of IL-1β in serum, and the cytokine was diffusely distributed throughout lesions, which was correlated with the numbers of parasites in the lesions. We propose that IL-1β possibly plays a key role in establishing the disease severity in patients infected with Leishmania mexicana.

Predictive factors for improvement of atrophic gastritis and intestinal metaplasia after Helicobacter pylori eradication: a three-year follow-up study in Korea

BACKGROUND AND AIMS

To date, data on the effects of anti-Helicobacter therapy on the improvement of atrophic gastritis (AG) and intestinal metaplasia (IM) have been conflicting. This study was performed to investigate whether eradication of H. pylori could lead to the improvement of AG and IM, and the prognostic factors associated with the improvement of AG and IM.

METHODS

Four hundred patients consisting of H. pylori-negative (n = 116) and H. pylori-positive (n = 284) groups were followed up 1 and 3 years after initial H. pylori tests. Serum levels of pepsinogen (PG), bacteria, environmental factors, and genetic polymorphisms were determined.

RESULTS

The grade of corpus atrophy decreased at 1 and 3 years after successful eradication (p < .001 and p = .033, respectively). However, there was no significant change in the IM in the antrum and in the corpus. Prediction factors for the improvement of corpus AG by H. pylori eradication were baseline low PG I/II ratio (≤3), high salt intake, and corpus-predominant gastritis. IM improvement was also associated with spicy food intake and high baseline grade of IM, in addition to these factors. In addition, IL-1B-511 C/T and IL-6-572 C/G alleles were found to inhibit IM improvement. However, H. pylori-negative and noneradicated group did not show any significant change in AG or IM.

CONCLUSION

Corpus AG was reversed by H. pylori eradication, and improvement of IM by H. pylori eradiation was more definite in patients with severe IM, low PG I/II ratio, and corpus-predominant gastritis, suggesting that H. pylori eradication is valuable even in severe cases.

Association of IL-10-1082 promoter polymorphism with susceptibility to gastric cancer: evidence from 22 case-control studies

Evidence suggested that interleukin-10 (IL-10) may be involved in the etiology of gastric cancer (GC). However, epidemiological studies on the association between IL-10-1082 promoter polymorphism and GC risk are still ambiguous. To quantitatively summarize the evidence for such a relationship, we performed a meta-analysis. Systemic searches of the PubMed and Medline databases were performed, with the last report up to July 2011. Crude odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of association. 22 independent studies including 4,289 cases and 5,965 controls were involved in this meta-analysis. Obvious association was found when all studies were pooled into the meta-analysis (A vs. G: OR = 0.489, 95% CI = 0.335-0.713, P < 0.001). In the subgroup analysis by ethnicity, we observed significant associations in Asians (A vs. G: OR = 0.651, 95% CI = 0.506-0.838, P = 0.001; AA vs. GG: OR = 0.482, 95% CI = 0.328-0.709, P < 0.001; AA/AG vs. GG: OR = 0.711, 95% CI = 0.527-0.959, P = 0.025; AA vs.

AG/GG

OR = 0.701, 95% CI = 0.520-0.944, P = 0.019) and Caucasians (A vs. G: OR = 0.365, 95% CI = 0.140-0.949, P = 0.039), but not in Latino population. When stratified analysis by control sources, our results indicated that A allele decreased approximately 48% risk among population-based studies (A vs. G: OR = 0.524, 95% CI = 0.374-0.733, P < 0.001). Taken together, this meta-analysis suggests that IL-10-1082 polymorphism is associated with GC risk.

A meta-analysis of interleukin-8 -251 promoter polymorphism associated with gastric cancer risk

Background

Potential functional allele A/T single nucleotide polymorphism (SNP) of Interleukin 8 (IL-8) promoter -251has been implicated in gastric cancer risk.

Methods

We aimed to explore the role of A/T SNP of IL-8 -251 in the susceptibility to gastric cancer through a systematic review and meta-analysis. Each initially included article was scored for quality appraisal. Desirable data were extracted and registered into databases. Eighteen studies were ultimately eligible for the meta-analysis of IL-8 - 251 A/T SNP. We adopted the most probably appropriate genetic model (codominant model). Potential sources of heterogeneity were sought out via stratification and sensitivity analyses, and publication biases were estimated.

Results

Between IL-8 -251 AA genotype with gastric cancer risk, statistically significant association could be noted with overall gastric cancer, evidently noted in Asians, witnessed in high quality subgroup, and apparently noted in intestinal-type gastric cancer.

Conclusions

Our meta-analysis indicates that IL-8 -251 AA genotype is associated with the overall risk of developing gastric cancer and may seem to be more susceptible to overall gastric cancer in Asian populations. IL-8 -251 AA genotype is more associated with the intestinal-type gastric cancer. IL-8 -251 AA genotype is not associated with Helicobacter Pylori infection status in our meta-analysis.

Impact

The analyses suggest that IL-8 -251 AA genotype may be an important biomarker of gastric cancer susceptibility for Asians, especially for Chinese Han population, the assumption that needs to be further confirmed in future well-designed studies in China.

Effects of interleukin-10 polymorphisms, Helicobacter pylori infection, and smoking on the risk of noncardia gastric cancer

Objective

Both variations in the interleukin-10 (IL10) gene and environmental factors are thought to influence inflammation and gastric carcinogenesis. Therefore, we investigated the associations between IL10 polymorphisms, Helicobacter pylori (H. pylori) infection, and smoking in noncardia gastric carcinogenesis in Koreans.

Methods

We genotyped three promoter polymorphisms (-1082A>G, -819T>C, and -592 A>C) of IL10 in a case-control study of 495 noncardia gastric cancer patients and 495 sex- and age-matched healthy controls. Multiple logistic regression models were used to detect the effects of IL10 polymorphisms, H. pylori infection, and smoking on the risk of gastric cancer, which was stratified by the histological type of gastric cancer.

Results

The IL10-819C and -592C alleles were found to have complete linkage disequilibrium, and all three IL10 polymorphisms were associated with an increased risk of intestinal-type noncardia gastric cancer. These associations were observed only in H. pylori-positive subjects and current smokers. A statistically significant interaction between the IL10-592 genotype and H. pylori infection on the risk of intestinal-type gastric cancer was observed (P for interaction  = 0.047). In addition, H. pylori-positive smokers who were carriers of either the IL10-1082G (OR [95% CI]  = 17.76 [6.17−51.06]) or the -592C (OR [95% CI]  = 8.37 [2.79−25.16]) allele had an increased risk of intestinal-type gastric cancer compared to H. pylori-negative nonsmokers homozygous for IL10-1082A and -592A, respectively. The interaction between the IL10-1082 polymorphism and the combined effects of H. pylori infection and smoking tended towards significance (P for interaction  = 0.080).

Conclusions

Inflammation-related genetic variants may interact with H. pylori infection and smoking to increase the risk of noncardia gastric cancer, particularly the intestinal-type. These findings may be helpful in identifying individuals at an increased risk for developing noncardia gastric cancer.

Variation in human genetic polymorphisms, their association with Helicobacter pylori acquisition and gastric cancer in a multi-ethnic country

BACKGROUND AND AIM

The contribution of human genetic polymorphisms to Helicobacter pylori infection and gastric cancer (GC) development remains unclear due to geographic variation in the association between specific host genetic polymorphisms and GC. In the current study we investigated the association between polymorphisms related to immune and cancer-related pathways and H. pylori infection among the major ethnicities, Chinese, Malay and Indian, resident in Singapore and Malaysia as well as the association between these polymorphisms and GC development in ethnic Chinese patients.

METHODS

Thirty-four polymorphisms in 26 genes were typed by mass spectrometry in 422 patients undergoing endoscopy (162 Chinese, 113 Indian and 87 Malay controls and 60 Chinese GC cases). Patients were assessed for evidence of H. pylori infection. Odds ratios (OR) and confidence intervals (CI) were obtained using logistic regression models.

RESULT

The prevalence of 16 polymorphisms varied significantly among the ethnicities. In the Chinese subgroup, nominally significant associations were shown between (i) EBBR2+1963G (rs1801200) and H. pylori infection (per-allele OR: 0.48, 95% CI 0.23, 0.98, P = 0.04), (ii) PTGS2-1195G (rs689466) and an increased risk of GC on adjusting for H. pylori status (OR: 1.53, 95% CI 0.99, 2.37, P = 0.05), and (iii) IL1B-1473C (rs1143623) and a decreased risk of GC (OR: 0.64, 95% CI 0.41, 0.99, P = 0.05). Borderline significant associations were seen between IL2-330G (rs2069762) (OR 1.45, 95% CI 0.95, 2.15, P = 0.06) and IL13-1111T (rs1800925) (OR 0.65, 95% CI 0.42, 1.01, P = 0.06) and H. pylori infection.

CONCLUSION

These findings contribute to the understanding of the genetic variation between ethnicities, which may influence H. pylori susceptibility and the outcome of infection.

The interleukin-10-1082 promoter polymorphism and cancer risk: a meta-analysis

Interleukin-10 (IL-10) is a multifunctional cytokine with both immunosuppressive and anti-angiogenic properties and play an important role in the pathogenesis of cancer. IL-10-1082A>G polymorphism is the most extensively studied polymorphism in the IL-10 gene in cancer susceptibility. To date, a number of case-control studies were conducted to investigate the association between IL-10-1082A>G polymorphism and cancer risk in humans. However, the association between the IL-10-1082A>G polymorphism and cancer risk is still ambiguous. In an effort to solve this controversy, we performed a meta-analysis based on 61 case-control studies, including 14,499 cancer cases and 16,967 controls. We used odds ratios (ORs) with 95% confidence intervals (CIs) to assess the strength of the association. In the stratified analyses by specific cancer type, increased risk was found in lung cancer (OR = 3.16, 95% CI = 1.16-8.63 for GA versus AA; OR = 2.07, 95% CI = 1.16-3.70 for GG versus AA; OR = 3.17, 95% CI = 1.31-7.68 for GA/GG versus AA) and non-Hodgkin's lymphoma (OR = 1.18, 95% CI = 1.02-1.36 for GA versus AA; OR = 1.17, 95% CI = 1.02-1.35 for GA/GG versus AA). The meta-analysis also indicated that the variant genotypes were associated with a moderately increased risk in Asians in all genetic models (OR = 1.80, 95% CI = 1.17-2.76 for GA versus AA; OR = 3.32, 95% CI = 1.62-6.82 for GG versus AA; OR = 1.67, 95% CI = 1.07-2.60 for GA/GG versus AA; OR= 2.93, 95% CI = 1.43-6.03 for GG versus AA/GA). The meta-analysis suggested that the IL-10-1082A>G polymorphism was associated with increased risk of cancer in Asians and lung cancer and non-Hodgkin's lymphoma. To draw comprehensive and true conclusions, more researches with larger numbers of worldwide participants are needed to examine associations between IL-10-1082A>G polymorphism and cancer risk.

The role of interleukin DNA polymorphisms in gastric cancer

Gastric carcinoma is one of the most widespread malignancies worldwide. Interleukins are the key group of cytokines which may have tumor-promoting or tumor-suppressing effect, and receptors for them, of course, have the same importance in this context. However, mechanisms of their impact on tumor are not fully understood up to date. Numerous studies provide conflicting data, that makes picture more confusing and complicated. It is known that single nucleotide polymorphisms in interleukin genes may dramatically affect on protein expression level, or alter its functions, which may lead to gastritis or ulcer, and eventually promote cancer occurrence. Furthermore, some of these genetic polymorphisms may serve as predictive factors for cancer prognosis and prevention. In order to understand the impact of each genetic polymorphism, the review of IL-1B, IL-4, IL-6, IL-8, IL-10, IL17A, IL-17F DNA polymorphisms on gastric carcinoma was done, and risk alleles were recommended for further research.

-251 T/A polymorphism of the interleukin-8 gene and cancer risk: a HuGE review and meta-analysis based on 42 case-control studies

The -251T/A (rs4073), a single nucleotide polymorphism, has been identified in the promoter region of the interleukin-8 (IL-8) gene. It's presence could influence the production of IL-8 protein by regulating the transcriptional activity of the gene. A large number of studies have been performed to evaluate the role of -251T/A polymorphism on various cancers, with inconsistent results being reported. In this paper, we summarized 13,189 cases and 16,828 controls from 42 case-control studies and attempted to assess the susceptibility of -251T/A polymorphism to cancers by a comprehensive meta-analysis. Pooled odds ratios and 95% confidence intervals were calculated by using the random-effects model. Publication bias, subgroup, and sensitivity analysis were also performed. Results showed that the carriers of the -251A allele had about a 12-21% increased risk for the reviewed cancer, in total. The carriers of -251A had an elevated risk to breast cancer, gastric cancer and nasopharyngeal cancer and a reduced risk to prostate cancer, but no evidence was found to indicate that the -251A allele predisposed its carriers to colorectal and lung cancers. When stratified separately by 'racial descent' and 'study design', it was found that the carriers of the -251A allele among the African group, Asian group and hospital-based case-control study group were at a higher risk for cancer, but not in European group and population-based case-control study. These results show that -251A allele is susceptible in the development of low-penetrance cancers.

Helicobacter pylori infection and nonmalignant diseases

Several interesting studies have been published on nonmalignant Helicobacter pylori-related conditions over the past year, which are reviewed in this article. A revival of interest in the histologic classification of gastritis has led to grading of gastritis into stages correlating with risk of neoplastic progression, new data to improve this concept have been published. Unselected prescription of proton-pump inhibitors in patients with dyspepsia has been questioned by the finding that withdrawal of proton-pump inhibitors induces acid-related symptoms in healthy volunteers, probably by the mechanism of rebound gastric acid hypersecretion. Additional data on the rationale of tapering proton-pump inhibitor therapy are therefore awaited. Moreover, new data on peptic ulcer disease and its complications provide clear recommendations for daily clinical practice. Testing and eradication of H. pylori in patients with peptic ulcer bleeding is essential. However, in H. pylori-negative peptic ulcer disease, high overall patient mortality should be acknowledged, and this should guide considering continuation of nonsteroidal anti-inflammatory drugs. The role of H. pylori in the pathogenesis of gastroesophageal reflux disease is still unclear. An association has been described by several studies; however, it cannot be translated to individual risks for development of gastroesophageal reflux disease after H. pylori eradication. Possibly, additional data on subgroups, such as gastric ulcer, duodenal ulcer patients, and associated gastric mucosal changes, will solve this issue.

IL-8 -251A/T polymorphism is associated with decreased cancer risk among population-based studies: evidence from a meta-analysis

Growing evidence suggests that interleukin-8 (IL-8) play pivotal roles in the pathogenesis of cancer through the modulation of tumour immune response or enhanced angiogenesis. A single nucleotide polymorphism, -251A/T, has been identified in the promoter region of the IL-8 gene and has been shown to influence its production. Results from previous studies on the association of -251A/T polymorphism with different cancer types remained contradictory. To assess the effect of -251A/T of IL-8 on cancer susceptibility, we conducted a meta-analysis, up to May 2009, of 14,876 cases with different cancer types and 18,465 controls from 45 published case-control studies. Summary odds ratios and corresponding 95% confidence intervals (CIs) for IL-8 polymorphism and cancer were estimated using fixed- and random-effects models when appropriate. The AA/AT genotypes were associated with a significantly increased risk of nasopharyngeal carcinoma when compared with TT genotype (OR=1.48; 95% CI, 1.16-1.89). Moreover, significantly elevated risks were observed in 'other cancers', and also in African population when population is concerned. Interestingly, when stratified separately by population-based studies and hospital-based studies, significantly elevated risk was found among hospital-based studies (OR=1.21, 95% CI, 1.07-1.37), whereas significantly decreased risk was found among population-based studies (OR=0.90, 95% CI, 0.83-0.97). This meta-analysis shows that IL-8 -251A/T polymorphism may play a complex role in cancer development.

Influence of interleukin polymorphisms on development of gastric cancer and peptic ulcer

Pro-inflammatory cytokines are produced in the gastric mucosa by inflammatory cells activated by chronic Helicobacter pylori (H. pylori) infection. Polymorphisms of these cytokine genes are associated with individual differences in gastric mucosal cytokine mRNA level, which result in differences in gastric mucosal inflammation, acid inhibition and gastroduodenal disease risk in response to H. pylori infection. Although polymorphisms of interleukin (IL)-1B, IL-1RN and TNF-A have been reported to relate well with gastric cancer and peptic ulcer risk, those of IL-2, IL-4, IL-6 and IL-8 genes are unclear. In combined analyses using data from previous studies, we found that the risk of gastric non-cardia cancer development was significantly associated with IL-4-168 C allele (OR: 0.81, 95% CI: 0.69-1.00) and IL-4-590 T allele carrier status (0.61, 0.53-0.73), and IL-6-174 G/G genotype (2.02, 1.31-3.10). In peptic ulcer development, IL-2-330 G and IL-4-590 T allele carriers had a significantly decreased risk (0.37, 0.27-0.50 and 0.58, 0.34-0.99, respectively). Moreover, IL-2, IL-4, IL-6 and IL-8 gene genotypes prevalence differs among populations. The inflammatory cytokine gene polymorphisms (e.g. IL-4-590 and IL-6-572 for gastric cancer, and IL-4-590, IL-6-572 and IL-8-251 for peptic ulcer) have a more potent influence on development of gastroduodenal diseases in Western than East Asian populations. These cytokine gene polymorphisms, as well as those of IL-1B, IL-1RN and TNF-A, may be used to identify groups at higher risk of gastric cancer and peptic ulcer, and those suitable for their prevention by H. pylori eradication therapy in Western populations.

The association between interleukin-10-592 polymorphism and gastric cancer risk: a meta-analysis

Relationship of gastric cancer with the presence of IL-10-592 polymorphism was reported with inconsistent results. The objective of this study was to quantitatively evaluate the association between IL-10-592 allele polymorphism and gastric cancer susceptibility. We performed an extensive search of relevant studies and made a meta-analysis, including 12 studies with 2,285 gastric cancer cases and 4,236 controls. The combined results based on all studies showed that there were no significant differences in genotype distribution between gastric cancer cases and controls, CC versus CA/AA (OR = 1.05, 95% CI: 0.92-1.18), CC/CA versus AA (OR = 1.16, 95% CI: 0.92-1.46), CC versus CA (OR = 1.03, 95% CI: 0.90-1.17), CC versus AA (OR = 1.10, 95% CI: 0.90-1.34), and CA versus AA (OR = 1.16, 95% CI: 0.92-1.45). When stratifying for the race, it was found that gastric cancer cases had a significantly higher frequency of CC/CA versus AA (OR = 1.31, 95% CI: (1.08-1.59) and a significantly upper frequency of CA versus AA (OR = 1.33, 95% CI: 1.09-1.63) than control in Asians. When stratifying for the location and the Lauren's classification of gastric cancer, there were no statistically significant differences in genotype distribution between gastric cancer cases and controls. This meta-analysis suggested that IL-10-592 allele polymorphism might be a risk factor for gastric cancer among Asians.

Effect of various noise sources on the detective quantum efficiency of phosphor screens

We have examined the effect of screen-structure, optical-detector, and secondary-quantum noise sources on detective quantum efficiency, DQE(f). This was done by using experimental measurements of screen-structure and optical-detector noise in combination with a theoretical model which predicts x-ray quantum and secondary-quantum noise for different optical and physical properties of a phosphor screen. The reduction in DQE(f) from noise sources other than x-ray quantum noise depends on the noise power spectra (NPS) of these other sources relative to the x-ray quantum NPS. Even though x-ray quantum noise may be the dominant noise source at low spatial frequencies, it decreases relatively rapidly with increasing frequency so that other noise sources, which may be small at low frequencies, dominate. Our model predicts that DQE(f) can be increased, at spatial frequencies less than 4 mm-1, by changing the optical properties of the screen even though modulation transfer function MTF(f) may decrease. Furthermore, if screen and optical-detector noise decrease with increasing frequency and secondary-quantum noise sufficiently small, then DQE(f) will also be improved at frequencies greater than 4 mm-1.