Having more gamma-H2AX may mean:
You will need specific experiments to distinguish these possibilities.
You could test your question by correlating samples that have been treated and then split them between gamma-H2AX detection (what is your method used?) and DNA damage quantification using a method like HPLC-tandem MS or FACS. The best thing would be to perform a time course, starting immediately after treatment (UV is great for that) and then extend the samples over time to see two things: 1. Does the amount of gamma-H2AX go up as DNA damage amounts increase and 2. Does the amount of gamma-H2AX decrease as DNA damage is repaired?
Gamma-H2AX is a phosphorylated form of one of the H2A variants. H2AX is phosphorylated by kinases activated by sensors of DNA damage, particularly of double strand breaks (ATM kinase recruitment by the MRN complex). Many scientists use H2Ax foci as readout for double strand breaks. As pointed out above, if the upstream pathway is intact, this is approximately valid. It is sometimes also used to look at DSB repair kinetics, as H2AX phosphorylation decreases after repair.
I would say that more H2AX foci indicates more DNA DSBs. To analyze the efficiency of the repair of such DSBs (better or worst DDR) you will need a kinetics to measure the rate of repair of your different experimental conditions
Jose is right, perform a time kinetic after 5Gy gamma irradiation to be sure, that the repair efficiency is not different. The highest gH2AX signal should be visible after 20min.
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