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

Abstract

Clearance of pulmonary infection with the fungal pathogen Cryptococcus neoformans is associated with the accumulation and activation of lung macrophages. However, the phenotype of these macrophages and the mechanisms contributing to their accumulation are not well-defined. In this study, we used an established murine model of cryptococcal lung infection and flow cytometric analysis to identify alveolar macrophages (AMs) and the recently described exudate macrophages (ExMs). Exudate macrophages are distinguished from AMs by their strong expression of CD11b and major histocompatibility complex class II and modest expression of costimulatory molecules. Exudate macrophages substantially outnumber AMs during the effector phase of the immune response; and accumulation of ExMs, but not AMs, was chemokine receptor 2 (CCR2) dependent and attributable to the recruitment and subsequent differentiation of Ly-6C high monocytes originating from the bone marrow and possibly the spleen. Peak ExM accumulation in wild-type (CCR2 ؉/؉ ) mice coincided with maximal lung expression of mRNA for inducible nitric oxide synthase and correlated with the known onset of cryptococcal clearance in this strain of mice. Exudate macrophages purified from infected lungs displayed a classically activated effector phenotype characterized by cryptococcal-enhanced production of inducible nitric oxide synthase and tumor necrosis factor ␣. Cryptococcal killing by bone marrow-derived ExMs was CCR2 independent and superior to that of AMs. We conclude that clearance of cryptococcal lung infection requires the CCR2-mediated massive accumulation of fungicidal ExMs derived from circulating Ly-6C high monocytes.

Altered Immune Response Differentially Enhances Susceptibility to Cryptococcus neoformans and Cryptococcus gattii Infection in Mice Expressing the HIV-1 Transgene

“…Among these, MCP-1, MIP-1␣, TNF-␣, and IFN-␥ all play a role in leukocyte recruitment to the lungs in response to C. neoformans infection (42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52). Accordingly, reduced production of these four cytokines may explain, at least in part, the strikingly sparse inflammatory cell response to C. gattii compared to that to C. neoformans in the non-Tg C3H mice.…”

“…During pulmonary C. neoformans infection, upregulation of MCP-1 and MCP-3 (CCL7) production is required for CCR2-mediated recruitment of T cells, dendritic cells, and macrophages, formation of bronchovascular cell infiltrates, and development of protective Th1 immunity (42)(43)(44)(45)(46)(47)(48). Furthermore, SJL/J mice, which are resistant to C. neoformans infection, show enhanced MCP-1 mRNA expression compared to susceptible C57BL/6 mice (62).…”

Analysis of Cell Cycle and Replication of Mouse Macrophages after In Vivo and In Vitro Cryptococcus neoformans Infection Using Laser Scanning Cytometry

“…he interaction of the human pathogenic fungus Cryptococcus neoformans with macrophages is thought to be a key event in the outcome of cryptococcal infection (10,13,17,28,29). C. neoformans is a facultative intracellular pathogen and, once within a macrophage, C. neoformans can replicate intracellularly with outcomes that range from host cell lysis to nonlytic exocytosis (2,3,23).…”

Susceptibility to Progressive Cryptococcus neoformans Pulmonary Infection Is Regulated by Loci on Mouse Chromosomes 1 and 9

“…In mice, clearance of C. neoformans requires CD4 ϩ and CD8 ϩ T-lymphocyte subsets (24,34), while antibody-mediated protective efficacy depends on several factors, including the host genetic background (44). Exudate macrophages that are derived from Ly6c-positive (Ly6c ϩ ) monocytes and recruited to the lung via a CCR2-dependent mechanism were also recently shown to mediate cryptococcal clearance (40). Notably, the susceptible C3H/HeN strain had significantly fewer CD8 ϩ T lymphocytes and CD19…”