Methods. We assessed cells obtained by BAL in subjects with mild atopic asthma and in normal control subjects for the expression of messenger RNA (mRNA) for interleukin-2, 3, 4, and 5, granulocyte-macrophage colony-stimulating factor (GM-CSF), and interferon gamma by in situ hybridization with P-32-labeled complementary RNA. Localization of mRNA to BAL T cells was assessed by simultaneous in situ hybridization and immunofluorescence and by in situ hybridization after immunomagnetic enrichment or depletion of T cells.

Results. As compared with the control subjects, the subjects with asthma had more BAL cells per 1000 cells that were positive for mRNA for interleukin-2 (P < 0.05), 3 (P < 0.01), 4 (P < 0.001), and 5 (P < 0.001) and GM-CSF (P < 0.001). There was no significant difference between the two groups in the number of cells expressing mRNA for interferon gamma. In the subjects with asthma, mRNA for interleukin-4 and 5 was expressed predominantly by T lymphocytes.

Conclusions. Atopic asthma is associated with activation in the bronchi of the interleukin-3, 4, and 5 and GM-CSF gene cluster, a pattern compatible with predominant activation of the T(H2)-like T-cell population.