Immunohistochemistry staining was performed on 4μm formalin-fixed paraffin-embedded sections. MC38 tumor staining was performed as previously described (59 (
link)) using
anti-CD45 (BD Bioscience, 550539) and anti-CD8 (Synaptic System, 361 003) antibodies employing a citrate buffer pressure cooker for antigen retrieval. For human tumor staining, all procedures were done on the automated Ventana
Discovery Ultra staining system. Sections were first deparaffinized using EZ prep solution and antigen retrieval was achieved using Cell Conditioning solution 1. Sections were blocked with
Discovery Inhibitor (all from Ventana). Sections were incubated with primary antibodies for 16 minutes for population markers and 12 hours for CXCL13 and CCL19 then washed and incubated with OmniMap anti-Mouse or anti-Rabbit conjugated with horseradish peroxidase (HRP) (Ventana, cat# 760-4310 and 760-4311) for additional 16 minutes. Discovery Purple or OmiMAP DAB chromogen kits (cat# 760-229 or 760-159) was then applied to generate a color reaction. Slides were then counterstained with hematoxylin II followed by bluing reagent (Ventana, cat# 790-2208 and cat# 760-2037). Primary antibodies used for staining were:
anti-CCL19 (RD Systems, cat# MAB361-100; 1:200) and
anti-CXCL13 (Abcam, cat# ab112521; 1:150), CD31 (Cell Marque, cat# 131M-94; 1:500);
αSMA (Abcam, cat# ab5694; 1:400).
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