Some populations of dendritic cells may be depleted by clodronate liposomes (Leenen et al., 1998), although effects of this treatment on lung dendritic cells remain poorly defined. We quantified numbers of dendritic cells in lungs of mice treated with clodronate or control saline liposomes. Clodronate liposomes did not affect total numbers of CD11c(+), MHC class II(+) dendritic cells in the lung interstitium as compared with control liposomes. In both groups, dendritic cells comprised ≈ 0.8% of total cells in the lungs, which is consistent with our previous data from untreated mice. Because antigen presenting cells such as dendritic cells and macrophages migrate to regional lymph nodes to initiate adaptive immunity, we also quantified numbers of these cell types in the tracheobronchial lymph node of mice 2 days after injection of liposomes. There were no significant differences between clodronate and saline control mice in numbers or percentages of CD11c(+), MHC class II(+) dendritic cells, Mac-3(+) macrophages, or ERMP-20(+) late monocyte progenitors in these lymph nodes (data not shown). Furthermore, numbers or percentages of dendritic cells and macrophages in peripheral blood, as determined by these same cell surface markers, did not differ between mice 2 days following treatment with clodronate or saline liposomes (data not shown). Collectively, these data demonstrate that intratracheal administration of clodronate liposomes depleted only alveolar macrophages.

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