Mode A depicts a competition on a receptor binding by a viral ligand that replaces the natural one. Examples for this mode are the expression of the secreted IL-10 ( Figure 2 ), IL-8 (UniProt: Q98158, Q98314, D2E2Z5) and PDGF (UniProtKB Q80GE8, Q2F842 and D0VXD7). These secreted mitogens are identified in class I and class VI viruses (Table 2) . Viral proteins participate in a rich protein-protein interaction (PPI) network [47] . Mode B illustrates PPI, where the virus uses an acquired sequence for replacing a host partner protein or for interacting with a preexisting protein complex. The result is an alteration of the cells' function. Examples for viral proteins that interfere with the host PPI are the anti-apoptotic Bcl-2 sequences and Profilin (Table 2, for example UniProt: Q5IXM3, P33828,  P68695) . Mammalian Semaphorins (Sema7) and the Smallpox virus A39R protein ( Table 2 , UniProt: Q775N9, B7SV99, Q0N658, A0ES13) share identical binding modes with a crossreactivity towards common receptors [48] .