Transfer of a CD4+ Th1 cell line to nude mice effects clearance of Rhodococcus equi from the lung

Rhodococcus equi, an intracellular respiratory pathogen, causes severe granulomatous pneumonia in humans with AIDS and in young horses. Pulmonary clearance of R. equi requires functional CD4(+) T cells and gamma interferon (IFN-gamma) expression from bronchial lymph node cells. The purpose of this study was to investigate whether R. equi-specific CD4(+) Th1 cells could effect clearance of R. equi from the lung. Adoptive transfer of a Th1 cell line into nude mice resulted in expression of IFN-gamma mRNA locally in bronchial lymph node cells and clearance of R. equi from the lungs. In contrast, mice transfused with a R. equi-specific CD4(+) Th2 cell line expressed interleukin-4 but not IFN-gamma mRNA, failed to clear pulmonary infection, and developed large granulomas in the lung. Control mice, which did not receive cells, did not produce IFN-gamma or interleukin-4 and developed small pulmonary granulomas. These results clearly show that a Th1 response is sufficient to effect pulmonary clearance of R. equi.