tokens: Bacterial suspensions were incubated at 37 degrees C for 45 minutes supplemented with 2 % mouse serum from Sigma - Aldrich ( St . Louis , MO . ) , heat inactivated mouse serum ( 56 degrees C 30 minutes ) , or bacteria alone and then added at an MOI of 10 : 1 to J774A . 1 cells in triplicate .