Elevated phagocytosis of bacteria by TREM-2 deficient AM.

(A) WT and Trem-2^−/− BMDM (n = 4–5 per genotype) were incubated with FITC labeled S. pneumoniae (MOI 100) and after 1 h phagocytosis was assessed using FACS. (B–C) WT and Trem-2^−/− AM (n = 4 per genotype) were incubated with FITC labeled S. pneumoniae (B) or E. coli (C) (MOI of 100) and phagocytosis was assessed using FACS 1 h later. (D) Elevated phagocytosis of S. pneumoniae by Trem-2^−/− AM as determined using confocal microscopy as described in the M&M section. The percentage of cells that contain bacteria is depicted (n = 4–5 per genotype). (E–F) WT and Trem-2^−/− AM (n = 4–5 per genotype) were incubated with FITC labeled S. pneumoniae (MOI 100) under either serum free conditions (SFM) or the bacteria were pre-opsonised with 10% anti-pneumococcal serotype III capsular antibody (ST3-Ab) (E) or 10% pooled WT mouse serum (F) for 30 min before addition to the cells. Phagocytosis was assessed 1 h later. (G) WT and Trem-2^−/− AM (n = 4 per genotype) were incubated with 1 µg/ml FITC labeled BSA or FITC labeled S. pneumoniae (MOI 100) and phagocytosis was assessed 1 h later by FACS. (H) WT and Trem-2^−/− AM (n = 4 per genotype) were incubated with FITC labeled S. pneumoniae strain 19A (MOI 100) and phagocytosis was assessed 1 h later by FACS. (I–L) WT and Trem-2^−/− mice (n = 7 mice per genotype) were intranasally infected with 10⁶ CFU FITC labeled S. pneumoniae for 4 h and in vivo phagocytosis by AM (I–J) and neutrophils (K–L) was determined. J and L show representative FACS plots of data in I and K. (M) WT and Trem-2^−/− mice (n = 6 mice per genotype) were intranasally infected with 10⁵ CFU S. pneumoniae and bacterial CFUs were enumerated 24 h post infection in the lung and BALF. All data represent mean ± SEM versus WT unless otherwise indicated. Data in (A–C, F and H) are representative of three independent experiments and all other data are representative of two independent experiments. * p<0.05, ** p<0.005, **** p<0.0001.