Figure 4.

Concepts represented as building blocks for effectiveness of cell-targeting Abs in immunity to viral infections. See text for details. Many factors—each with its own quantitative or qualitative dimension—contribute additively or synergistically to reaching a threshold of antiviral activity that meets a standard of protective efficacy (as defined in Box 1). The threshold is not a constant, but varies by individual, host species, virus biotype, dose and route of infection, etc. In short, the figure is intended to illustrate that Fc-mediated aspects of Ab-mediated immunity are interrelated parts of a complex adaptive system that arose during co-evolution of host and virus. To adequately exploit these concepts with vaccines or therapeutic Abs requires either empirical good fortune (the key to almost all licensed vaccines) or understandings that allow rational improvements in design. In the search for statistical or mechanistic correlates of protection, assays that combine several of these factors may be favored.