Is Mycoplasma Pneumonia associated with childhood acute lymphoblastic leukemia?

Improvement of purine and pyrimidine antimetabolite-based anticancer treatment by selective suppression of mycoplasma-encoded catabolic enzymes

Most mycoplasmas are present as commensals, colonising the mucosa of our respiratory and gastrointestinal tract. Experimental data suggest that the long-term association of certain mycoplasma species with mammalian cells might favour host-cell transformation and malignancy. Moreover, increased mycoplasma infection has been noted in several cancers. Despite efforts to develop target-specific anticancer drugs, current cancer treatment still relies on the use of nucleobase or nucleoside-based analogues. Here, we provide experimental evidence that nucleoside-metabolising catabolic enzymes expressed by mycoplasmas substantially compromise the efficacy of nucleoside antimetabolites used in the treatment of cancer. We also suggest potential methods for improving future chemotherapy by suppressing mycoplasma-mediated catabolism of the anticancer nucleoside analogues.

Does population mixing measure infectious exposure in children at the community level?

Epidemiological studies focusing on the etiology of childhood chronic diseases have used population mixing as a proxy for the level of infection circulating in a community. We compared different measures of population mixing (based on residential migration and commuting) and other demographic variables, derived from the United Kingdom Census, with hospital inpatient data on infections from two Government Office Regions in England (Eastern and the West Midlands) to inform the development of an infectious disease proxy for future epidemiological studies. The association between rates of infection and the population mixing measures was assessed, using incidence rate ratios across census areas, from negative binomial regression. Commuting distance demonstrated the most consistent association with admissions for infections across the two regions; areas with a higher median distance travelled by commuters leaving the area having a lower rate of hospital admissions for infections. Deprived areas and densely populated areas had a raised rate of admissions for infections. Assuming hospital admissions are a reliable indicator of common infection rates, the results from this study suggest that commuting distance is a consistent measure of population mixing in relation to infectious disease and deprivation and population density are reliable demographic proxies for infectious exposure. Areas that exhibit high levels of population mixing do not necessarily possess raised rates of hospital admissions for infectious disease.

Can mycoplasma-mediated oncogenesis be responsible for formation of conventional renal cell carcinoma?

OBJECTIVES

To investigate the association between Mycoplasma sp. infection and conventional renal cell carcinoma (RCC).

METHODS

Normal kidney, renal intratubular neoplasia, and tumor tissue samples from 33 patients with RCC and 35 healthy controls were studied. Molecular DNA analysis was done after nested polymerase chain reaction performed in two steps with seven primers (four outer and three inner) that can recognize at least 15 different Mycoplasma sp.

RESULTS

Mycoplasma sp. DNA was detected in normal kidney, renal intratubular neoplasia, and tumor tissue samples at a ratio of 36%, 67%, and 82%, respectively. In 6 of the 33 patients with RCC, no Mycoplasma sp. was detected from any of the three tissue samples. Mycoplasma sp. DNA was detected in only 5 (14%) of the 35 samples from the control group.

CONCLUSIONS

The relationship between mycoplasma infection and conventional RCC has been investigated for the first time, and a significantly high existence of Mycoplasma sp. DNA was found in the tissues of patients with conventional RCC compared with that found in a healthy control group. This suggests that mycoplasma-mediated multistage carcinogenesis may play a role in the development of RCC.

Associations between three types of maternal bacterial infection and risk of leukemia in the offspring

A case-control study was nested within two maternity cohorts with a total of 7 million years of follow-up for assessment of the role of bacterial infections in childhood leukemia. Offspring of 550,000 mothers in Finland and Iceland were combined to form a joint cohort that was followed for cancer up to age 15 years during 1975-1997 through national cancer registries. For each index mother-case pair, three or four matched control mother-control pairs were identified from population registers. First-trimester serum samples were retrieved from mothers of 341 acute lymphoblastic leukemia cases and 61 other leukemia cases and from 1,212 control mothers. Sera were tested for antibodies to the genus Chlamydia, Helicobacter pylori, and Mycoplasma pneumoniae. Odds ratios and 95% confidence intervals, adjusted for sibship size, were calculated as estimates of relative risk. M. pneumoniae immunoglobulin M appeared to be associated with increased risk (odds ratio (OR) = 1.6), but the association lost statistical significance when the specificity of the immunoglobulin M was considered (OR = 1.5, 95% confidence interval: 0.9, 2.4). In Iceland, H. pylori immunoglobulin G was associated with increased risk of childhood leukemia in offspring (OR = 2.8, 95% confidence interval: 1.1, 6.9). Since H. pylori immunoglobulin G indicates chronic carriage of the microorganism, early colonization of the offspring probably differs between Iceland and Finland, two affluent countries.

An infectious aetiology for childhood acute leukaemia: a review of the evidence

There are three current hypotheses concerning infectious mechanisms in the aetiology of childhood leukaemia: exposure in utero or around the time of birth, delayed exposure beyond the first year of life to common infections and unusual population mixing. No specific virus has been definitively linked with childhood leukaemia and there is no evidence to date of viral genomic inclusions within leukaemic cells. The case-control and cohort studies have revealed equivocal results. Maternal infection during pregnancy has been linked with increased risk whilst breast feeding and day care attendance in the first year of life appear to be protective. There is inconclusive evidence from studies on early childhood infectious exposures, vaccination and social mixing. Some supportive evidence for an infectious aetiology is provided by the findings of space-time clustering and seasonal variation. Spatial clustering suggests that higher incidence is confined to specific areas with increased levels of population mixing, particularly in previously isolated populations. Ecological studies have also shown excess incidence with higher population mixing. The marked childhood peak in resource-rich countries and an increased incidence of the childhood peak in acute lymphoblastic leukaemia (ALL) (occurring at ages 2-6 years predominantly with precursor B-cell ALL) is supportive of the concept that reduced early infection may play a role. Genetically determined individual response to infection may be critical in the proliferation of preleukaemic clones as evidenced by the human leucocyte antigen class II polymorphic variant association with precursor B-cell and T-cell ALL.

Perinatal exposure to infection and risk of childhood leukemia

BACKGROUND

A population-based case-control study was conducted to investigate the association between childhood leukemia and infectious exposures during pregnancy and early neonatal period.

PROCEDURE

Children born and diagnosed with leukemia between 1973 and 1989 in Sweden (578 lymphatic, 74 myeloid) were selected as cases. One control was randomly selected for each case and individually matched by sex, month, and year of birth. Children with Down's syndrome were excluded. Exposure data were blindly abstracted from antenatal, obstetric, and other standardized medical records. Odds ratios (OR) and 95% confidence intervals (CI) were calculated by conditional logistic regression.

RESULTS

A history of maternal infection was not significantly associated with childhood leukemia, OR = 1.25 (95% CI 0.95-1.65). Maternal lower genital tract infection significantly increased the risk of childhood leukemia, OR = 1.78 (95% CI 1.17-2.72), and especially for children over 4 years of age at diagnosis, OR = 2.01 (95% CI 1.12-3.80). Neonatal infection was not associated with the risk of leukemia. The results remained unaltered after adjustment for potential confounders, and separate analyses for myeloid and lymphoid leukemia.

CONCLUSIONS

We could document an association between exposure to maternal lower genital tract infection in utero, and a subsequent risk for childhood leukemia, which indicate the importance of an early exposure.

Do mycoplasmas cause human cancer?

A linkage between mycoplasmas and malignancy was mainly proposed in the 1960s when human-associated mycoplasmas were becoming of interest given the novel characterization of the human respiratory pathogen Mycoplasma pneumoniae. Associations with leukemia and other malignancies, however, were largely ascribed to tissue-culture contamination, which is now recognized as a significant potential problem in molecular biology circles. A few epidemiological studies, however, continue to raise concern over such a linkage. As well, in vitro data have demonstrated the potential for some mycoplasmas to induce karyotypic changes and malignant transformation during chronic tissue-culture infestation. As cellular and molecular mechanisms for such transformation become studied, a resurgence of interest in this area is inevitable. A role for mycoplasmas in malignancy of any sort is conjectural, but there remains a need to continue with focussed epidemiological and laboratory investigations.Key words: mycoplasma, cancer, oncogenesis, leukemia.

Prenatal epidemiology of pediatric tumors

With the exception of a small percentage of cases attributable to hereditary cancer syndromes (eg, familial retinoblastoma) or genetic syndromes (Down syndrome), the etiology of most childhood cancers is unknown. Recent epidemiologic studies have focused on the prenatal period and have investigated potential associations with parental age, cigarette smoking, birth weight of the child, parental occupational exposures, and specific environmental exposures. The following challenges lie ahead for future epidemiologic studies of childhood cancer: 1) improvement of diagnostic classification; 2) improved methods for exposure assessment; 3) evaluation of data from molecular biology to generate biologically derived hypotheses; and 4) incorporation of markers of genetic susceptibility when feasible.

Breast-feeding and risk of childhood acute leukemia

BACKGROUND

Breast-feeding is well known to have a protective effect against infection in infants. Although the long-term effects of breast-feeding on childhood cancer have not been studied extensively, a protective effect against childhood Hodgkin's disease and lymphoma has been suggested previously from small investigations. In this study, we tested the hypothesis that breast-feeding decreases the risk of childhood acute leukemia.

METHODS

A total of 1744 children with acute lymphoblastic leukemia (ALL) and 1879 matched control subjects, aged 1-14 years, and 456 children with acute myeloid leukemia (AML) and 539 matched control subjects, aged 1-17 years, were included in the analysis. Information regarding breast-feeding was obtained through telephone interviews with mothers. All leukemias combined, histologic type of leukemia (ALL versus AML), immunophenotype of ALL (early pre-B cell, pre-B cell, or T cell), and morphology of AML were assessed separately in the data analysis.

RESULTS

Ever having breast-fed was found to be associated with a 21% reduction in risk of childhood acute leukemias (odds ratio [OR] for all types combined = 0.79; 95% confidence interval [CI] = 0.70-0.91). A reduction in risk was seen separately for AML (OR = 0.77; 95% CI = 0.57-1.03) and ALL (OR = 0.80; 95% CI = 0.69-0.93). The inverse associations were stronger with longer duration of breast-feeding for total ALL and AML; for M0, M1, and M2 morphologic subtypes of AML; and for early pre-B-cell ALL.

CONCLUSION

In this study, breast-feeding was associated with a reduced risk of childhood acute leukemia. If confirmed in additional epidemiologic studies, our findings suggest that future epidemiologic and experimental efforts should be directed at investigating the anti-infective and/or immune-stimulatory or immune-modulating effects of breast-feeding on leukemogenesis in children.

Association of childhood leukaemia with factors related to the immune system

The childhood peak of common acute lymphoblastic leukaemia has been proposed as being a rare response to delayed exposure to a common infection. In this context, factors related to the child's immune system are of special interest. Information on such factors was obtained in a recent German case-control study comprising more than 1000 children with acute leukaemia. Neither being the first-born child, nor a short duration of breastfeeding, indicators of a deficit in viral contacts during infancy or the number of infectious diseases, were significant risk factors. We observed a strong association with fewer routine immunizations with a 3.2-fold increase for those children getting less than four immunizations, but this association could partly be explained by reporting bias. While tonsillectomy or appendectomy increased the risk of leukaemia in our studies, a protective effect of allergies could be seen. In summary, we found only weak support for the delayed exposure hypothesis. To some extent this may be due to the chosen surrogate markers which reflect, rather indirectly, immunological isolation in infancy and delayed exposure to common viruses. However, the significant findings for routine immunizations, tonsillectomy and allergies of the child or its parents merit further investigation.

The causes of acute leukemia

Although impressive biologic advances have increased understanding of leukemogenesis, we know little about the causes of the acute leukemias. Epidemiologic studies have focused primarily on children. Higher birth weight is associated with an increased risk of childhood acute leukemia. Several theories have been advanced that may account for these observations, and additional biologic studies are needed. Some epidemiologic studies suggest that the acute leukemias in children may have an infectious component. Again, further work, especially in the area of specific causative agents, is necessary. Another area for future epidemiologic study includes investigation of exposure to natural and synthetic DNA topoisomerase II inhibitors. Preliminary evidence suggests that exposure to these agents, which are found in certain foods and medications, may be related to the subsequent development of acute leukemia in infants.