CCR2+ Monocyte-Derived Dendritic Cells and Exudate Macrophages Produce Influenza-Induced Pulmonary Immune Pathology and Mortality

Abstract

Infection with pathogenic influenza virus induces severe pulmonary immune pathology, but the specific cell types that cause this have not been determined. We characterized inflammatory cell types in mice that overexpress MCP-1 (CCL2) in the lungs, then examined those cells during influenza infection of wild-type (WT) mice. Lungs of both naive surfactant protein C-MCP mice and influenza-infected WT mice contain increased numbers of CCR2+ monocytes, monocyte-derived DC (moDC), and exudate macrophages (exMACs). Adoptively transferred Gr-1+ monocytes give rise to both moDC and exMACs in influenza-infected lungs. MoDC, the most common inflammatory cell type in infected lungs, induce robust naive T cell proliferation and produce NO synthase 2 (NOS2), whereas exMACs produce high levels of TNF-α and NOS2 and stimulate the proliferation of memory T cells. Relative to WT mice, influenza-infected CCR2-deficient mice display marked reductions in the accumulation of monocyte-derived inflammatory cells, cells producing NOS2, the expression of costimulatory molecules, markers of lung injury, weight loss, and mortality. We conclude that CCR2+ monocyte-derived cells are the predominant cause of immune pathology during influenza infection and that such pathology is markedly abrogated in the absence of CCR2.

Chemokine Receptor 2-Mediated Accumulation of Fungicidal Exudate Macrophages in Mice That Clear Cryptococcal Lung Infection

“…45 Our gating strategy distinguishes ExMs from AMs, which are both CD11c ϩ AF ϩ on the basis of CD11b expression (present on ExMs and absent on AMs), as recently described. [33][34][35][36] In those studies, ExMs were specifically identified in the lungs of mice with bacterial or viral pneumonia, in which the numbers were much smaller than in the current study. The impressive quantity of ExMs that we identify in this model likely reflects the substantial inflammation induced by cryptococcal lung infection, with recruitment of up to 100 million CD45 ϩ leukocytes per mouse and critical reliance on lung macrophages for clearance of this organism.…”

“…Therefore, we evaluated ExM expression of the cell surface molecule Ly-6C as a marker of newly differentiated myeloid cells. 33,56,57 ExMs recovered at 7 dpi strongly express Ly-6C, whereas expression was diminished at 14 and 21 dpi (Figure 3). By 28 dpi, the few remaining ExMs expressed almost no Ly-6C.…”

“…Next, we set consecutive gates which identified CD11c ϩ cells ( Figure 1A, left dot plot) and distinguished autofluorescent (AF ϩ ) macrophages from non-AF (AF Ϫ ) dendritic cells (DCs) ( Figure 1A, middle dot plot), as previously described. 41,45,[51][52][53] Last, we used relative expression of CD11b to distinguish CD11b-negative AMs (CD11c ϩ AF ϩ CD11b Ϫ ) 42,54,55 and CD11b-positive ExMs (CD11c ϩ AF ϩ CD11b ϩ ) 33,35 ( Figure 1A, right dot plot; gates labeled AM and ExM). Proper gate placement for AF and expression of CD11c and CD11b were determined using AMs obtained from bronchoalveolar lavage fluid of uninfected mice (which consists of Ͼ90% CD11c ϩ AF ϩ CD11b Ϫ AMs; data not shown).…”

“…[33][34][35][36] Expression of CD11b, along with varying reports of increased major histocompatibility complex (MHC) class II and costimulatory molecules, distinguishes ExMs from AMs. 33 Exudate macrophages express iNOS indicative of effector function. 34 Whether ExMs are present in mice with cryptococcal lung infection is unknown.…”

Origin and functional specializations of DC subsets in the lung

“…2), and found that CD103 1 CD11b À DC migrate from their intraepithelial base to the draining MLN [2]. The disappearance of this CD11b À population from the trachea was accompanied by an influx of CD11b 1 DC, representing inflammatory-type Ly6C 1 DC [46]. Inflammatory DC expressed B220 and BST2 (120G8) in addition to high levels of CD11c and CD11b [14].…”