RT-PCR analysis of the expression of the messages for IL-15, TNF-, and IFN-γ by AM of a representative healthy subject cultured for 24 hours in medium alone and in the presence of IL-15. The figure shows a representative healthy subject (subject #2) but a consistent pattern of expression was observed in five consecutively examined normal subjects. 96% of BAL cells of subject #2 were alveolar macrophages and 4% lymphocytes, as determined by morphological evaluation and the CD4/CD8 ratio was 2.1. AM were enriched as reported in the Materials and Methods section.