Allergen-induced CD11b+ CD11cint CCR3+ macrophages in the lung promote eosinophilic airway inflammation in a mouse asthma model

Although the recruitment of macrophages to the lung is a central feature of airway inflammation, its function in ongoing T(h)2 cell-mediated eosinophilic airway inflammation remains controversial. Here, we have demonstrated that the allergen-induced CD11b(+) CD11c(int) macrophage expressing CC chemokine receptor 3 (CCR3) in the lung performs a crucial function in the induction of eosinophilic asthma in a murine model. In the lungs of normal mice, residential cells evidencing high granularity phenotypically evidenced CD11b(int) CD11c(+) or CD11b(+) CD11c(int) cells, appearing at a 2:1 ratio. After allergen challenge, however, this reverses dramatically, up to a ratio of one to six. Approximately 91% of increased CD11b(+) CD11c(int) cells evidenced the expression of the CCR3 eotaxin receptor, but not other chemokine receptors, such as CCR5 and CXCR4. Interestingly, the CD11b(+) CD11c(int) cells purified from the lungs of OVA (ovalbumin)-sensitized and challenged mice evidenced higher antigen-presenting activity than was observed in CD11b(int) CD11c(+) cells. In order to investigate the in vivo function of CD11b(+) CD11c(int) cells, the cells were isolated from the lungs of OVA-sensitized and challenged mice and then adoptively transferred prior to the allergen challenge of normal mice. In the CD11b(+) CD11c(int)-transferred mice airway hyperresponsiveness, eosinophilic inflammation in the lung and T(h)2 cytokine secretion in the bronchoalveolar lavage fluids were significantly enhanced as the result of OVA challenge, as compared with the mice that received OVA-primed CD90(+) T cells or CD11b(int) CD11c(+) cells. These findings show that CD11b(+) CD11c(int) macrophages expressing CCR3 as key pro-inflammatory cells are both necessary and sufficient for allergen-specific T cell stimulation during ongoing eosinophilic airway inflammation.