Comparison of Cytokine Responses (IL-21, IL-12, IL-13) in Chlamydia pneumoniae-Stimulated PBMC in Asthma and Non-Asthma

Objective: Chlamydia pneumoniae (C. pneumoniae) is a gram-negative intracellular bacterium that causes respiratory infections in humans. C. pneumoniae is responsible for cell activation and production of cytokines that may contribute to inflammatory responses in asthma. Cell-mediated immune responses are important for protective immunity; however, these responses may be impaired in asthma. In this study, we examined cytokine responses (IL-21, IL-12, IL-13) responsible for T helper (Th)1 versus Th2 responses in C. pneumoniae-stimulated PBMC from subjects with or without asthma. These cytokines could be potential biomarkers in the evaluation of past C. pneumoniae infection.

Methods: Peripheral blood mononuclear cells (PBMC) (1×10⁶/mL) from stable adult asthmatic (N=6) and non-asthmatic subjects (N=6) were infected +/- C. pneumoniae TW-183 at a multiplicity of infection (MOI)=0.1, using dose responses (1:10, 1:100), and cultured 48 hrs. Cytokine responses (Interleukin (IL)-21, IL-12, IL-13) were measured in supernatants (ELISA).

Results: Cytokine responses (mean differences: unstimulated-stimulated cells) were significant for IL-12 (1:10, 1:100) (P=0.0005, 0.0005) but not for IL-21 or IL-13 (Wilcoxon signed-rank test). Cytokine levels were higher in asthmatic subjects for IL-13 (mean differences: non-asthma-asthma) (unstimulated, 1:10, 1:100) (-210±167, -140±113, -89±59, respectively) (P=0.05, 0.05, 0.05, respectively) compared with non-asthma. However, IL-21 and IL-12 responses were similar in both groups. When subjects were stratified according to C. pneumoniae IgG antibody status, no significant differences in cytokine responses were observed.

Conclusion: Differential cytokine patterns in subjects with or without asthma may suggest a mechanism for the development of persistent infection with C. pneumoniae.