| Background and objective Mycoplasma pneumoniae(MP) is a common pathogen of respiratory disease in children, devoid of cell wall, able to invade airway epithelial cells. It firstly causes the respiratory infection, but it also induces the extrapulmonary manifestations. Because without cell wall, some antibiotics such as penicillin, cephalosporin have no effect on the treatment of MP. In the other hand, the treatment of MP infection with macrolides easily induces resistance to macrolides. More and more medical investigators attached importance to the MP infection. So to study the pathophysiology and explore the pathogenesis mechanisms was important for the treatment of MP infection. Some study indicated that the number of eosinophils and neutrophils in the peripheral blood increased in patients with MP infection, these results suggested that eosinophils and neutrophils might play an important role in the pathogenesis of MP. Within the cytokines correlated to the eosinophils, Interleukin-5 (IL-5) is the most important. IL-5 is a cytokine produced mainly by activated Th2 cells, and it stimulates the proliferation and differentiation of eosinophils in the bone marrow and the release of mature eosinophils from the bone marrow into the blood, up-regulates the expression of sICAM 1, which permit egression of eosinophils from the vasculature to the airway mucosa. IL-5 can contribute eosinophils to release toxic proteins which take part in the asthma, and also inhibit the eosinophils necrosis to prolong their survival. Within the inflammatory mediators correlated to the eosinophils, the function of cysteinyl leukotrienes(cysLTs) is stronger. CysLTs are synthesized via 5-lipoxygenase metabolism of arachidonic acid. CysLTs contribute to accumulation of eosinophils within airways and eosinophils are also the source of CysLTs. CysLTs act with cytokines each other. IL-5 stimulates eosinophils to increase the production of CysLTs. The cysLT1-R antagonists can reduce the level of IL-5 significantly. Some study indicated that Leukotriene E4 (LTE4) is excreted into the urine in a relatively constant proportion of 4-7% and the measurement of LTE4 in urine is a method for assessing changes of cysteinyl leukotrienes in the body And within the inflammatory mediators correlated to the neutrophil, Leukotriene B4(LTB4) is the more important. LTB4 is synthesized via 5-lipoxygenase metabolism of arachidonic acid. LTB4 is a major inflammatory mediator produced by neutrophils and can increase the number of neutrophil strongly and is one of the strongest chemotactic andactive factor of neutrophils. In hypersensitivity inflammatory reaction, the increase of LTB4 induces the inflammatory cells to zoom in inflammatory tissue which increases the vascular permeability and results in edema. There was little study on the IL-5 in the pathogenesis of MP at home and abroad, and there was no report on the LTB4 and cysLTs in the pathogenesis of MP. In this study we tested the serum concentration of IL-5, LTB4 and the urine concentration of LTE4 in patients with MP infection, to explore the value of IL-5, LTB4 and cysLTs on the MP infection and to provide theoretic evidence for clinical treatment. Subjects and methods: 1. Subjects enrolled: 1.1 The MP infection group: we enrolled 29 patients with MP infection in our department from June 2005 to September 2005, including male (14) and female (15) whose age from 0.5 to 13 years old (3.52+ 3.08). The diagnosis criteria were referred to MP infection criteria of our contrary. According to the severity, the patients with MP infection was divided into mild infection group (5/29), median infection group (17/29) and severe infection group (7/29). 1.2 The non-MP infection group: we enrolled 30 patients with respiratory infection except MP infection in our department from June 2005 to September 2005, including male (16) and female (14) whose age from 0.42 to 8.58 years old (3.75+ 2.62). Of all, 4 patients were with upper respiratory disease and 26 were with lower respiratory disease. 1.3 The normal control group: we enrolled 30 healthy children with routing physical examinations in outpatient department from June 2005 to September 2005, including male (15) and female (15) whose age from1.92 to 12.08 years old (3.77+ 1.69). There was no significant difference in sex and age between three groups (P>0.05). 2. Methods: 2.1 Criteria enrollment 2.1.1 Criteria enrollment for the MP infection group: The subjects are with respiratory disease with MP-IgM positive aged from 3 month to 14 years old, without other infections, immune diseases or chronic diseases. 2.1.2 Criteria enrollment for the non-MP infection group: The subjects are with respiratory disease and MP-IgM negative aged from 3 month to 14 years old, without immune diseases or chronic diseases. 2.1.3 Criteria enrollment for the normal control group: The subjects are healthy children with routing physical examinations in outpatient department and with MP-IgM negative aged from 3 month to 14 years old, without immune diseases, chronic diseases or infection disease within one month. 2.2 Collection for specimen: All of Subjects enrolled were exsanguinated 2 ml blood for the subjects tested MP-IgM after separating the serum and collected 2 ml urine and the serum with MP-IgM positive or MP-IgM negative. All the specimens were kept below -20℃. 2.3 Test for specimen: Tested the serum concentration of IL-5, LTB4 and the urine concentration of LTE4 by ELISA. All manipulations were referred to the reagent directions. 3. Statistical methods: All data collected with non-normal distribution were transferred to the data with normal distribution by logarithmic transform. Used M/Q or X+SD to describe the quantity variable and ANOVA was used to compare the means among different groups, while the difference among different groups was tested by Tamhane's test or LSD test according to thehomogeneity test. Used ratio or rate to describe the categorical date and chi-square was used to compare the ratio or rate among different groups. Used Pearson Correlation analysis to analyze the correlation of quantity data; and used the Spearman test to analyze the correlation of rank data. Used the SPSS 12.0 to statistical analysis, P value<0.05 were considered statistically significant. Results 1. The change of serum IL-5 in three groups: The serum concentration of IL-5 in the MP infection group was higher than in the non-MP infection group and the normal control group, but there was no significant difference among the three groups (F=2.208, P>0.05). 2. The change of serum LTB4 in three groups: There was significant difference among the three groups(F=9.282,P<0.05). The serum concentration of LTB4 in the MP infection group was higher than that in the non-MP infection group, but there was no significant difference between the two groups(T=0.637,P>0.05);The serum concentration of LTB4 in the MP infection group was significantly higher than that in the normal control group(T=4.033,P<0.05);The serum concentration of LTB4 in the non-MP infection group was also significantly higher than that in the normal control group (T=3.778, P<0.05). 3. The change of urinary LTE4 in three groups: There was significant difference among the three groups(F=19.269,P<0.05).The urine concentration of LTE4 in the MP infection group was higher than that in the non-MP infection group, but there was no significant difference between the two groups(T=0.121,P>0.05);The urine concentration of LTE4 in the MP infection group was significantly higher than that in thenormal control group(T=5.406,P<0.05);The urine concentration of LTE4 in the non-MP infection group was also significantly higher than that in the normal control group (T=5.330, P<0.05). 4. Pearson Correlation analysis of serum IL-5, LTB4 and urinary LTE4 in the MP infection group. 4.1. There was no correlation between the serum IL-5 and the serum LTB4 (r=0.275, P>0.05), neither between the serum IL-5 and the urinary LTE4 (r= -0.086, P>0.05) in the MP infection group. 4.2. There was positive correlation between the serum LTB4 and the urinary LTE4 in the MP infection group(r=0.38, P<0.05). 5. Spearman test to analyze the correlation between the severity and serum IL-5, LTB4, urinary LTE4. 5.1 There was no correlation between the severity and the serum IL-5(r=0.031, P>0.05), neither between the severity and the urinary LTE4 (r=0.302, P>0.05) in the MP infection group. 5.2 There was positive correlation between the serum LTB4 and the severity in the MP infection group(r=0.414, P<0.05). Conclusions 1. IL-5 might be not an important factor in the pathogenesis mechanisms of MP infection. 2. LTB4 plays an role in the pathogenesis mechanisms of MP infection and it has some value that its change evaluate the severity. The concentration is higher, the severity is more serious. 3. CysLTs takes part in the pathogenesis mechanisms of MP infection. 4. It might be one of the pathogenesis mechanisms of asthma evoked easily after MP infection that LTB4 and cysLTs increase.5. In MP infection it might be through increasing the activity of 5-lipoxygenase to produce more LTB4 and cysLTs. 6. There might be no important significance for the change of serum LTB4 and urinary LTE4 to distinguish MP infection and non-MP infection. 7. In the inflammatory reaction of MP infection eosinophils and neutrophils might act mainly through the LTB4 and cycLTs not through IL-5.
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