LPS-induced CD11b+Gr1(int)F4/80+ regulatory myeloid cells suppress allergen-induced airway inflammation

In humans, the bacterial product lipopolysaccharide (LPS) has been associated with protection from allergic diseases such us asthma. However, in mouse models of allergic asthma, differential effects of LPS have been noted based on the dose. A low dose of LPS promotes Th2 responses and allergic disease but a high dose has been associated with suppression of allergic airway inflammation. Our recent work has described the ability of LPS to increase the frequency of CD11b+Gr1(int)F4/80+(abbreviated as Gr1(int) cells) cells in the lung tissue of mice in a dose-dependent fashion that is dependent on TLR4 and the TLR adaptor protein, MyD88. Both phenotypically and morphologically, the cells were found to have similarities with mycloid-derived suppressor cells. Adoptive transfer of LPS-induced Gr1(int) cells suppressed allergen-induced airway inflammation suggesting regulatory functions of the cells in allergic asthma. Although the Gr1(int) cells are detectable in the lung tissue of LPS-treated mice, they are barely detectable in the lung-draining lymph nodes (Lns) or in the airway lumen. This causes selective enrichment of these cells over dendritic cells (Dcs) in the tissue which upon LPS stimulation migrate to lung-draining LNs. The Gr1(int) cells were found to blunt the ability of the lung DCs to upregulate GATA-3 or to promote STAT5 activation in primed Th2 cells, both transcription factors having critical roles in TH2 effector function. Thus, a complete understanding of the generation and regulation of the Gr1(int) cells would provide new avenues to either promote or delete these cells for disease-specific immunoregulation.