its seems Ok for me to have a low titer after panning as you are selecting the phages that stick to your protein, then you need to amplify what you got and reselect the same way... and thus enrich progressively in phages that interact with your protein..

I think there might be a problem somewhere. First of all, are you sure about using 10^15 phage? That seems very very high to me, I've never heard of titers in that range. 10^13 maybe but 10^15 seems way to high and suggests you have phage contamination somewhere that is leading to an observed high titer.

Secondly, what is the complexity of your phage display library? Let us say you have a really rich library of 10^9 in complexity (and usually it is less than that). In a library of 10^15 phage if you had only 1 single phage type that could bind, then you should have recovered 10^6 assuming 100% recovery. And there are likely to be many more than 1 single binding phage in the population so I would expect more binders.

Didier Poncet

Thanks

Michael J. Benedik

Thanks for your answer.

I amplified the library in 4 Lit of 2x-YT media so I got that titer. Yes I found that for the first round I should start with lower titer to enrich the target antibody and I tried it several times. But it seems that the titer of my antigen is too less and I need to amplify it and then do 2-3 rounds of panning.