In all cases, one major difficulty is that the host proteins may be essential for the cells and their depletion may lead to cytotoxicity, thus proper controls are needed. In addition, the host proteins might be essential for the virus within the cells but only accessory within the virions. Consequently, depletion of a protein may have limited impact on the virus since complemented by the other pool of that protein in the virus or the cell. Small reduction or stimulation in viral yields may thus result. It such cases, it may be necessary to produce the virus on cells that lack these proteins to see if this makes a difference. One should also consider animal models since tissue culture based screens may miss important players, for instance modulators of the immune system or virulence factors. Clearly, multiple experimental strategies are needed to ultimately insure the biological significance of the host proteins found in viral particles.