Chest
Volume 121, Issue 5, May 2002, Pages 1493-1497
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Clinical Investigations
Pneumonia
Role of Interleukin-18 and T-helper Type 1 Cytokines in the Development of Mycoplasma pneumoniae Pneumonia in Adults

https://doi.org/10.1378/chest.121.5.1493Get rights and content

Study objective

Interleukin (IL)-18 is a proinflammatory cytokine, originally termed interferon (IFN)-γ-inducing factor, which promotes T-helper type 1 (Th1) cytokine responses. We recently reported that serum IL-18 levels were elevated in children with Mycoplasma pneumoniae pneumonia (MP). In this study, we investigated the contribution of IL-18 to the infection and assessed the Th1 cytokine response to pulmonary involvement in adults.

Methods

We investigated the clinical course, pulmonary involvement, and serum levels of IL-18, IFN-γ, IL-12p40, and soluble IL-2 receptor (sIL-2R) in 21 patients with acute-stage MP and in 21 age- and sex-matched control subjects.

Results

Significantly (p < 0.001) increased serum IL-18 (median, 248 pg/mL [range, 89 to 441 pg/mL] vs median, 126 pg/mL [range, 47 to 217 pg/mL]) and sIL-2R (median, 617 U/mL [range, 410 to 1,032 U/mL] vs median, 425 U/mL [range, 268 to 601 U/mL]) were found in patients with MP as compared with healthy control subjects, and there was a tendency toward increased serum IFN-γ and IL-12p40. Circulating IL-18 values had a positive correlation with serum sIL-2R levels (r = 0.62, p = 0.028) and the number of affected pulmonary lobes (σ = 0.61, p = 0.024), but not with the serum levels of antibodies to M pneumoniae, IFN-γ, or IL-12p40. Serum IL-18 and sIL-2R values in severe cases were significantly higher (p < 0.03) than those in mild cases. IFN-γ and sIL-2R levels in four patients with pleural effusion were significantly (p < 0.05) higher than those in the other 17 subjects.

Conclusions

Serum levels of IL-18 were raised during the acute phase of MP. We suggest IL-18 and Th1 cytokines may play a significant role in the immunopathologic responses in MP.

Section snippets

Study Population

Twenty-one patients with MP (median, 34 years; range, 20 to 64 years; 17 women and 4 men) and 21 sex- and age-matched healthy subjects (median, 33 years; range, 20 to 61 years; 17 women and 4 men) were recruited from Sapporo Medical University Hospital and Kushiro City General Hospital after giving informed consent. All patients were febrile with a persistent cough and were admitted to the hospital because of acute pneumonia. We excluded patients with the following conditions: (1) purulent

Results

Significantly higher levels of serum IL-18 (median, 248 pg/mL [range, 89 to 441 pg/mL] vs median, 126 pg/mL [range, 47 to 217 pg/mL]; p < 0.0001) and sIL-2R (median, 617 U/mL [range, 410 to 1,032 U/mL] vs median, 425 U/mL [range, 268 to 601 U/mL]; p < 0.0001) were found in patients with MP as compared with healthy control subjects (Fig 1). There was a nonsignificant trend to an increase in serum IFN-γ (median, 0.61 pg/mL [range, < 0.1 to 12.7 pg/mL] vs median, < 0.1 pg/mL [range, < 0.1 to 0.71

Discussion

In this study, serum IL-18 levels in patients with severe MP were higher than those in mild cases, and the IL-18 levels, but not serum IFN-γ levels, correlated with the number of affected lobes detected by CT scans. We have previously shown that IL-18 levels are high when pleural effusion is associated with MP.18 IL-18 can induce granulocyte/macrophage colony-stimulating factor and upregulate the intercellular adhesion molecule 1 expression in a monocyte cell line; thus, the effects of IL-18 on

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