Objective: In connection with the possible relationship between Mycoplasma infection and the onset of asthma, several studies have shown not only a high level of serum total immunoglobulin E (IgE) but also the production of IgE specific to Mycoplasma or common allergens during the course of Mycoplasma infection. It has been suggested that the balance of T helper type 1 (TH1)/T helper type 2 (TH2) immune response may regulate the synthesis of IgE. The objective of this study was to investigate the pattern of cytokine response (TH1 or TH2) during an episode of acute lower respiratory tract infection caused by Mycoplasma pneumoniae.
Study design: Using a bronchoalveolar lavage (BAL) with flexible bronchoscopy procedure, this study determined the levels of interleukin (IL)-2, interferon (IFN)-gamma (TH1), and IL-4 (TH2) in the supernatant of BAL fluid as well as the BAL cellular profiles of patients with Mycoplasma pneumonia (n = 14). These results were compared with those of patients with pneumococcal pneumonia (n = 12) or those of children with no identifiable airway infections (control group: n = 8).
Results: The BAL cellular profile in the Mycoplasma pneumonia group was characterized by a high percentage of neutrophils and lymphocytes. A significantly increased level of IL-2 was found in both pneumonia groups, compared with the control group. In contrast, the IFN-gamma level was not different for the 3 groups. The level of IL-4 and ratio of IL-4/IFN-gamma were significantly elevated in the Mycoplasma pneumonia group, but not in the pneumococcal pneumonia group, compared with the controls.
Conclusions: IL-4 levels and IL-4/IFN-gamma ratios in BAL fluid are significantly higher in patients with Mycoplasma pneumonia than in patients with pneumococcal pneumonia or control participants. The BAL cytokine data suggest a predominant TH2-like cytokine response in Mycoplasma pneumonia, thus representing a favorable condition for IgE production.