Poly lys

Recombinant Staphyloccocus Enterotoxin type E (SEE, Cellgenetech, MBS1112600), Ionomycin (407950; Calbiochem), PMA (Sigma-Aldrich, 79346) and Poly-l-lysine (Poly-Lys, Sigma-Aldrich, P8920) were used.
For detailed information on dilutions, companies, and reference numbers see Supplementary Table 1.

The adhesion assay was performed as previously reported39 (link). Briefly, 1 × 10⁵ B16/F10 cells per 100 μl RPMI 1640 (Life technologies) containing 0.1% (v/v) BSA (Sigma-Aldrich, Catalogue number A 2058), labelled with the fluorescent dye FAST DiI (1:100 dilution), were added to a 96-well plate (Iwaki, Bibby Scientific Italia, Italy) for 35 min at 37 °C in an air/CO₂ incubator. The wells were coated with BSA, C1q (Sigma-Aldrich Catalogue number C1740), and FN (Roche Life Science, Catalogue number 11051407001) used at the concentration of 20 μg ml⁻¹ in pH>9 sodium bicarbonate-buffered medium (100 mM). PolyLys (Sigma-Aldrich, Catalogue number P7280) was used as a negative control. After incubation, the unbound cells were removed and the number of adherent cells was counted with Infinite200 (absorbance 544 nm, emission 590 nm) (TECAN Italia, Italy) and referred to a calibration curve established with an increasing number of labelled cells.