Peroxidase

The streptavidin alkaline phosphatase method was adapted to detect the viral antigen using a polyclonal anti-ZIKV antibody produced at the Evandro Chagas Institute^{2 (link)}. The biotin-streptavidin peroxidase method was used for immunostaining of tissues with antibodies specific for each marker studied. First, the tissue samples were deparaffinized in xylene and hydrated in a decreasing ethanol series (90%, 80%, and 70%). Endogenous peroxidase was blocked by incubating the sections in 3% hydrogen peroxide for 45 min. Antigen retrieval was performed by incubation in citrate buffer, pH 6.0, or EDTA, pH 9.0, for 20 min at 90 °C. Nonspecific proteins were blocked by incubating the sections in 10% skim milk for 30 min. The histological sections were then incubated overnight with the primary antibodies diluted in 1% bovine serum albumin (Supplementary Table S1). After this period, the slides were immersed in 1 × PBS and incubated with the secondary biotinylated antibody (LSAB, DakoCytomation) in an oven for 30 min at 37 °C. The slides were again immersed in 1X PBS and incubated with streptavidin peroxidase (LSAB, DakoCytomation) for 30 min at 37 °C. The reactions were developed with 0.03% diaminobenzidine and 3% hydrogen peroxide as the chromogen solution. After this step, the slides were washed in distilled water and counterstained with Harris hematoxylin for 1 min. Finally, the sections were dehydrated in an increasing ethanol series and cleared in xylene.

Standard IHC protocol was followed to stain the tumor tissue samples using the mouse monoclonal antibody against hNIS (human Sodium Iodide Symporter) (Abcam, ab17795), ER (Estrogen Receptor) (Abcam, ab16660, ab288). Briefly, 5 µm sized paraffin embedded tissue sections were de-paraffinized with xylene and endogenous peroxidase activity was quenched with 3% H₂O₂ in methanol for 30 minutes in the dark. Tissue sections were dehydrated through graded alcohols and subjected to antigen retrieval using 10mM sodium citrate. Sections were washed with TBST (Tris Borate Saline Tween-20) and then blocked with 5% BSA (Bovine Serum Albumin) for one hour. Slides were incubated with the respective mouse monoclonal primary antibody diluted with TBS. Slides were then washed for 5 minutes in TBST and incubated for 1 hour with the respective HRP (Horse Raddish Peroxidase) conjugated anti-mouse secondary antibody diluted with TBS in a ratio of 1∶200. After washing, slides were incubated with DAB (3,3′-diaminobenzidine tetrahydrochloride) (Sigma) and immediately washed under tap water after color development. Slides were then counter stained with hematoxylin. Slides were mounted with DPX (dibutyl phthalate xylene) and were then observed under a light microscope (Carl Zeiss).

The muscles were cut on a cryostat at − 23 °C (7 μm), air-dried, and stored at − 20 °C. Slides were air-dried, rehydrated, and fixed in 4% paraformaldehyde (PFA) for 20 min at the time of staining. For CD63/DAPI/laminin staining, sections were incubated with mouse anti-CD63 IgG1 antibody (1:100 dilution, ab108950, Abcam, Cambridge, UK) and rabbit anti-laminin IgG antibody (1:100 dilution, L9393, Sigma-Aldrich, St. Louis, MO) overnight at 4 °C. Slides were washed in PBS, then incubated with Alexa Fluor 488 goat anti-mouse IgG1 (1:250 dilution, A11001, Invitrogen, Waltham, MA) and Alexa Fluor 594 goat anti-rabbit IgG (1:250 dilution, A11012, Invitrogen) secondary antibodies for 1 h at room temperature. Slides were washed in PBS and mounted with VectaShield fluorescent mounting media with DAPI (H-1200-10, Vector Laboratories, Newark, CA). For CD9/DAPI/dystrophin staining, sections were incubated with rabbit anti-CD9 IgG (1:100 dilution, SA35-08, Invitrogen) and mouse anti-dystrophin IgG2b (1:250 dilution, 08168, Sigma-Aldrich) overnight, followed by incubation with Alexa Fluor 594 goat anti-rabbit IgG (1:250 dilution, A11012, Invitrogen) and Alexa Fluor 647 goat anti-mouse IgG2b (1:250 dilution, A32728, Invitrogen) for 1 h at room temperature. For CD81/DAPI/dystrophin staining, sections were incubated with rabbit anti-CD81(1:100 dilution, SN206-01, Novus Biologicals, Centennial, CO) and mouse anti-dystrophin IgG2b (1:250 dilution, 08168, Sigma-Aldrich) overnight, followed by incubation with Alexa Fluor 594 goat anti-rabbit IgG (1:250 dilution, A11012, Invitrogen) and Alexa Fluor 647 goat anti-mouse IgG2b (1:250 dilution, A32728, Invitrogen) for 1 h at room temperature. For Pax7/CD9/DAPI/WGA staining, sections were subjected to epitope retrieval using sodium citrate (10 mM, pH 6.5) at 92 °C, followed by blocking of endogenous peroxidase activity with 3% hydrogen peroxide in PBS. Sections were incubated overnight in mouse anti-Pax7 IgG1 (1:100 dilution, Developmental Studies Hybridoma Bank, Iowa City, IA) and rabbit anti-CD9 IgG (1:100 dilution, SA35-08, Invitrogen), followed by incubation in goat anti-mouse biotin-conjugated secondary antibody (dilution 1:1,000, 115-065-205; Jackson ImmunoResearch, West Grove, PA) and Alexa Fluor 647 goat anti-rabbit IgG (1:250 dilution, A32733, Invitrogen) for 1 h at room temperature. Next, sections were incubated with streptavidin-HRP (1:500 dilution, S-911, Invitrogen) and Texas Red-conjugated Wheat Germ Agglutinin (WGA) (1:50 dilution, W21405, Invitrogen) at room temperature for 1 h, before incubation in Tyramide Signal Amplification (TSA) Alexa Fluor 488 (1:500 dilution, B40953, Invitrogen). Sections were mounted with VectaShield fluorescent mounting media with DAPI (H-1200-10, Vector Laboratories).
Images were captured with a Zeiss upright microscope (AxioImager M1, Oberkochen, Germany). To quantify the percentage of nuclei (DAPI+) expressing CD63, MyoVision software was used for automated analysis of nuclear density in cross-sections [39 (link)], and nuclei-expressing CD63 (identified as DAPI+/CD63+ events) were counted manually in a blinded manner by the same assessor for all sections using the Zen Blue software.

In the ZSH cohort, TMAs containing 259 ICC specimens were constructed as previously described [31 (link)–33 (link)]. For IHC staining of TMAs, following blocking endogenous peroxidase and antigen retrieval, the slides were stained using antibodies of CD8 (1:100, Cat# ab101500, Abcam, Cambridge, UK), Foxp3 (1:100, Cat# ab20034, Abcam), CD73 (1:500, Cat# 13160S, CST, Danvers, USA), HHLA2 (1:100, Cat# ab214327, Abcam), CD68 (1:8000, Cat# ab213363, Abcam), and CD163 (1:500, Cat# ab189915, Abcam). IHC staining of the TMA slides was performed according to the procedures described before [32 (link)].

The paraffin-embedded tissue sections were deparaffinized and rehydrated following standard procedures. Sections were incubated with 3% H₂O₂ to block endogenous peroxidase activity and antigen retrieval was performed in citrated buffer at 110 ℃, for 5 min in a pressure cooker. After the citrated buffer reached room temperature, the sections were removed and incubated overnight with the primary antibodies COL2A1 (1:200, bioss, bs-10589R) and SOX9 (1:1000, Abcam, Cat# ab185966) at 4 ℃, followed by incubation with an HRP conjugated secondary antibody (Beyotime Institute of Biotechnology, Inc., Nantong, China) for 2 h at room temperature. Peroxidase binding for both COL2A1 and SOX9 was visualized using diaminobenzidine. Then, the nuclei were counterstained with hematoxylin, while the slides were dehydrated, mounted, and analyzed with a light microscope. For the quantitative analysis, all positively stained cells, including those in the femoral condyle and tibial plateau area, on the articular surface per specimen were counted, and the percentage of positive cells was calculated using Image-Pro Plus 6.0.