Cellular immunity is activated and a TH-2 response is associated with early wheezing in infants after bronchiolitis

Objective: To determine whether abnormalities of cellular immunity are present and linked to early wheezing after bronchiolitis. Methods: We prospectively studied 26 infants hospitalized for a first episode of bronchiolitis and without any prior immune, cardiac, or respiratory disease. Blood was obtained at the time of enrollment and 5 months later for the assessment of the total cellular and differential counts, CD4^+ (helper) and CD8^+ (suppressor/cytotoxic) lymphocytes, and the activation markers CD23 (low-affinity immunoglobulin E receptor) and CD25 (interleukin-2 [IL-2] receptor). The cytokines interferon gamma (T-helper [TH] type-1 cytokine) and IL-4 (TH-2) were measured in plasma and in vitro after stimulation with IL-2 or with the house-dust mite (Dermatophagoides farinae) antigen. A daily log of episodes of wheezing was kept by parents after discharge. Results: We found an increase in blood eosinophils, an increased percentage of CD4^+, CD25^+, and CD23 ^+ lymphocytes in subjects at 5 months compared with the time of bronchiolitis and with healthy subjects of the same age (p <0.05). Plasma IL-4 levels, although not different from those of healthy subjects, also increased significantly. Peripheral blood lymphocytes from infants who wheezed produced more IL-4 in vitro, 5 months after bronchiolitis, in response to D. farinae antigen. In babies who wheezed, a positive correlation was found between the total number of days that wheezing occurred and the blood eosinophil count. Babies who wheezed more often (>20 days) had more peripheral blood basophils and eosinophils, and peripheral blood lymphocytes obtained from these subjects at the time of bronchiolitis produced less interferon gamma on stimulation with IL-2. Conclusions: Bronchiolitis is followed by activation of cellular immunity, and early wheezing in infants is associated with a TH-2 response. (J Pediatr 1997;130:584-93)