Figure 1.

Additive and/or synergistic effector responses induced by LABAs and glucocorticoids (GCs). A. LABAs and GCs may each induce a set of responses (sets A and B respectively) that do not interact. The net effect of a LABA/GC combination treatment would be the sum of the responses produced by each drug alone (A + B). B. While LABAs and GCs each induce a set of responses (sets A and B respectively), a number of these responses may be modulated by both LABAs and GCs. In these situations, where A ∩ B, there may be no interaction between each response, and the net effect is one of simple additivity. This is shown for a hypothetical gene (gene X) that was induced by LABA or GC. In this situation, the overall effect is the sum of the responses produced by each drug (A + B). Alternatively, responses in the overlap region, A ∩ B, may show interaction between the two drugs. This is shown for a hypothetical gene, gene Y, which is modestly induced by maximally effective concentrations of a LABA and by a GC, but together, there is a large induction of gene expression. As this is greater than the sum of the components, this can be described as synergy. In this situation, the overall effect of each drug is greater than the simple sum of A + B.