GC formation is intact in Stat3^fl/flCD19^Cre/+ mice. (A) PNA staining of spleens from Stat3^fl/flCD19^+/+ (Wt) and Stat3^fl/flCD19^Cre/+ (KO) hRBC-immunized mice shows equivalent GC formation. (B) Spleen cells from hRBC-immunized Wt and KO mice were analyzed by flow cytometry for GL7 expression to confirm equivalent GC formation. After mounting in Permamount solution (Sigma, St. Louis, MO), images were visualized using a Leica DMR microscope (Leica, Heidelberg, Germany) equipped with a 10×/0.3 objective lens and a 10× eyepiece, for a total original magnification of ×100. A Diagnostic CE230 SPOT camera (Diagnostic Instruments, Sterling Heights, MI) was used to capture images, and SPOT acquisition software (Diagnostic Instruments) was used to process and export them in Tagged Image File format (TIFF) to the canvas program (ACD Systems, Miami, FL) for further processing.