Association between Mycoplasma pneumoniae pneumonia and interleukin-17: insights and interpretative cautions from a meta-analysis

We sincerely thank Arredondo Montero (1) for his valuable comments on our systematic review and meta-analysis titled “Association of Serum Interleukin-17 Level and Mycoplasma pneumoniae Pneumonia in Children: A Systematic Review and Meta-analysis”, published in the Transl Pediatr (2). We appreciate his feedback; however, there appears to be a misunderstanding regarding the objective of our study. Therefore, the authors emphasize that the objective should be appraised to ensure accurate interpretation of the findings.

The primary aim of our research was to examine the association between serum interleukin-17 (IL-17) levels and Mycoplasma pneumoniae pneumonia (MPP) in children—not to evaluate IL-17 as a diagnostic tool, nor to assess its diagnostic accuracy as a standalone biomarker for MPP. Therefore, we did not conduct a meta-analysis to estimate diagnostic metrics such as sensitivity, specificity, or area under the curve (AUC), as suggested.

It is important to emphasize that our study does not propose serum IL-17 as a single diagnostic marker for MPP. We fully agree that relying on a single cytokine to diagnose a complex infectious disease is inappropriate. Accordingly, in our discussion, we noted that our findings could support MPP diagnosis when IL-17 detection is combined with other biomarkers, such as tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) or additional cytokines, alongside standard diagnostic methods. This integrative approach may improve diagnostic accuracy and aid in distinguishing healthy individuals from those with severe or non-severe MPP.

In general, MPP can be diagnosed using various methods, including culture, serological testing, and molecular assays. Among these, serological tests—particularly those detecting Mycoplasma pneumoniae (M. pneumoniae)-specific immunoglobulin M (IgM) antibodies—are the most commonly used in clinical practice (3). The studies included in our review primarily relied on clinical symptoms in conjunction with at least serological testing for IgM detection or polymerase chain reaction (PCR), in accordance with current guidelines (4). In certain cases, additional diagnostic tools such as PCR and radiological imaging were utilized to support the diagnosis, particularly in severe or refractory presentations. Nevertheless, in all included studies, the final diagnosis of MPP was ultimately confirmed based on the presence of clinical symptoms and positive IgM titers. Subsequently, a subgroup analysis was conducted to further explore the results. When comparing studies that used symptoms and serological testing alone versus those that used symptoms combined with serological testing and PCR, no statistically significant difference was observed between the two groups (P=0.17). However, this finding should be interpreted with caution due to the limited sample size; larger-scale studies are warranted to validate these results.

We conducted our review following the PRISMA guidelines and assessed study quality using the Newcastle–Ottawa Scale for both cohort and case-control studies. However, we did not follow the PRISMA-DTA guidelines, which are specifically designed for diagnostic test accuracy (DTA) meta-analyses, nor did we use the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool to assess methodological quality, as our study was not designed to evaluate DTA. While we aimed for methodological consistency, heterogeneity may still exist due to variations in the assays used to detect IL-17 in serum. He mentions that we used a random-effects model only when heterogeneity exceeded an I² of 25% and the P value from Cochran’s Q test was <0.1. This threshold is arbitrary and inconsistent with current meta-analytical standards, especially in biomarker research where between-study heterogeneity is expected. Moreover, we try to seek out the source of heterogeneity when I² is higher than 50% by performing subgroup analysis. However, our aim was to investigate the association between MPP and changes in serum IL-17 levels in pediatric patients. Therefore, we applied this threshold as a meta-analytical standard for clinical studies, not for DTA studies (5).

Although IL-17 has been widely implicated in autoimmune diseases, cancer, and various inflammatory conditions (6), its role and serum levels in MPP remain unclear. Moreover, the absence of a standardized method for measuring serum IL-17 levels limits its diagnostic utility. Therefore, caution should be exercised when interpreting IL-17 concentrations in the context of MPP. We further compared IL-17 levels based on the detection methods used—enzyme-linked immunosorbent assay (ELISA) versus magnetic bead-based assays. Studies using ELISA reported a mean difference (MD) of 112.59 pg/mL (95% CI: 62.54–182.64, I² =99.36%), whereas those using magnetic bead-based techniques showed a much lower MD of 1.99 pg/mL (95% CI: −0.89 to 4.86, I² =81.96%). Additionally, most of the studies employed ELISA (n=5), while only two studies utilized magnetic bead-based methods.

In our study, we used the DerSimonian and Laird (DL)method to evaluate the association between serum IL-17 levels and MPP in pediatric patients, as it is one of the most commonly used methods for fitting random-effects models. According to existing literature (7), when the number of studies (n) is around 8 or more, most methods produce reliable results (7). Our analysis included 7 studies, which is close to this threshold and generally considered acceptable for applying the DL method. Based on this method, we observed a statistically significant elevation in serum IL-17 levels among pediatric patients with MPP compared to healthy controls (MD =33.94 pg/mL; 95% CI: 24.66–43.22; P<0.01). However, heterogeneity was detected (I² =99.07%; P<0.01). To ensure the robustness of our findings, we also performed a restricted maximum likelihood (REML) analysis, which confirmed a statistically significant association between serum IL-17 levels and MPP in pediatric patients, demonstrating a significant association between elevated serum IL-17 levels and MPP (MD =117.52 pg/mL; 95% CI: 3.39–231.64; P=0.04), albeit with even higher heterogeneity (I² =100.00%; P<0.01).

We acknowledge that using Begg’s test with only five or six studies is not appropriate, as the Cochrane Handbook explicitly recommends applying these tools only when at least ten studies are available. This recommendation is due to the high risk of spurious asymmetry and unreliable estimates in smaller samples. Although asymmetry in the funnel plot was observed, we clearly stated in the limitations section that these findings should be interpreted with caution. To further assess potential bias, we conducted a sensitivity analysis, which indicated the presence of publication bias.

The heterogeneity across studies was extremely high (I² >99%) and had not been thoroughly investigated. Therefore, we conducted a meta-regression and subgroup analyses based on assay method and risk of bias. Our findings indicated that both the assay method and risk of bias were significant sources of heterogeneity (P<0.05). In addition, we performed a sensitivity analysis on different methods of estimating effect size and MPP confirmation, as shown in Table 1. We found that the results from DL were robust when the number of studies was greater than six for both estimators. However, REML had more inflated error rates when the combined studies had unequal sizes and between-study heterogeneity (7). This finding aligns with previous studies, which suggest that REML and the Hartung-Knapp-Sidik-Jonkman method provide better estimates when small studies (fewer than 5 studies) are included (8,9).

We appreciate the reviewer’s observations regarding the presentation of results in our research article. As noted, the included studies reported their findings using various formats, such as charts, tables, interquartile range (IQR), mean with standard deviation (SD), or standard error of the mean (SEM). For example, Chen et al. (10) reported their data as mean ± SEM, while others presented their findings using a bar chart or graph.

To ensure consistency in our meta-analysis, we converted all reported values to mean ± SD prior to statistical pooling. Therefore, we recommend that readers interpret the data with caution, particularly in light of these conversions and the variability in reporting formats.

We also agree with the reader’s comment regarding the inclusion of diagnostic accuracy metrics. For future meta-analyses focusing on diagnostic biomarkers, it would indeed be beneficial to include measures such as sensitivity, specificity, and AUC to provide a more comprehensive evaluation.

Several limitations of our study have been acknowledged in the discussion section. One key limitation is the relatively small sample size across the included studies. Additionally, all studies were conducted in China, which may limit the generalizability of our findings to broader or more diverse populations.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Editorial Office, Translational Pediatrics. The article did not undergo external peer review.

Funding: None.

Conflicts of Interest: The authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-377/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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