Am. J. Respir. Cell Mol. Biol., Volume 26, Number 6, June, 2002 671-679

Dendritic Cells and the Regulation of a Granulomatous Immune Response in the Lung

Kazuhiro Iyonaga, Karin M. McCarthy, and Eveline E. Schneeberger

Department of Pathology, Massachusetts General Hospital, Boston, Massachusetts

To investigate the contribution of dendritic cells (DC) in a pulmonary granulomatous immune response, C57BL/l6 mice, nonimmunized or immunized with purified protein derivative (PPD) of Mycobacterium bovis, were intravenously injected with PPD-coated Sepharose-4B beads. One and three days later lungs were harvested, granuloma size was measured, and immunolabeled cells in granulomas were counted. On Day 1, granulomas in immunized mice were 3-fold larger and contained more major histocompatibility complex class II⁺, CD11c⁺ DCs than nonimmunized mice. By Day 3, these differences had diminished. In all granulomas MHC class II⁺, CD11c⁺ DCs were in contact with the beads. By in situ hybridization these DCs expressed interleukin (IL)-12 p40 mRNA. MOMA2⁺ macrophages were present throughout the granulomas, whereas CD4⁺ and CD8⁺ T cells were localized at the granuloma periphery. DCs isolated from granulomatous lungs at Day 1, and from thoracic lymph nodes (LNs) at Days 1 and 3, stimulated PPD-specific T cell proliferation without exogenously added antigen, indicating that they had acquired bead-bound antigen. By Day 3, however, granuloma DCs presented little antigen, suggesting that newly immigrated DC lacked access to antigen or that antigen uptake/processing was inhibited. RNase protection assays of whole-lung mRNA showed increased interferon-, IL-1, IL-1 receptor antagonist, IL-6, and macrophage inhibitory factor, but no IL-10 mRNA on Days 1 and 3. These observations support the premise that DCs are key in initiating granulomatous cell-mediated immunity. However, factors generated within the granuloma downregulate the antigen presenting function of DC by Day 3 in this experimental model.