Statistical analyses were performed with GraphPad Prism 6.0 software. Mean values ± standard deviation (S.D.) are presented. The assay cut-off value is set to two standard deviations over the background signal according to Nordengrahn et al. . The background signal is estimated with a pair of antibodies that is known to not interact. Samples with values below this cut-off are considered to be negative for the interaction of interest while samples with values higher than the threshold are positive.