This invention provides, and in certain specific but non-limiting aspects relates to: —assays that can be used to predict whether a given ISV will be subject to protein interference as described herein and/or give rise to an (aspecific) signal in such an assay (such as for example in an ADA immunoassay). Such predictive assays could for example be used to test whether a given ISV could have a tendency to give rise to such protein interference and/or such a signal； to select ISV's that are not or less prone to such protein interference or to giving such a signal； as an assay or test that can be used to test whether certain modification(s) to an ISV will (fully or partially) reduce its tendency to give rise to such interference or such a signal； and/or as an assay or test that can be used to guide modification or improvement of an ISV so as to reduce its tendency to give rise to such protein interference or signal； —methods for modifying and/or improving ISV's to as to remove or reduce their tendency to give rise to such protein interference or such a signal； —modifications that can be introduced into an ISV that remove or reduce its tendency to give rise to such protein interference or such a signal； —ISV's that have been specifically selected (for example, using the assay(s) described herein) to have no or low(er)/reduced tendency to give rise to such protein interference or such a signal； —modified and/or improved ISV's that have no or a low(er)/reduced tendency to give rise to such protein interference or such a signal.ある種の具体的だが非限定的な態様では、本発明は、所定のＩＳＶが、本明細書において記載されるタンパク質干渉を受け、及び／又はアッセイ（例えば、ＡＤＡ免疫アッセイなど）において（非特異的）シグナルを生じさせるかを予測するのに使用され得るアッセイに関する。このような予測アッセイは、例えば、所定のＩＳＶが、このようなタンパク質干渉及び／又はこのようなシグナルを生じさせる傾向を有し得るかを試験するのに使用され得；このようなタンパク質干渉又はこのようなシグナルの発生の傾向がないか又は前記傾向がほとんどないＩＳＶを選択するのに使用され得；ＩＳＶに対するある種の改変が、このような干渉又はこのようなシグナルを生じさせる傾向を（完全に又は部分的に）減少させるかを試験するのに使用され得るアッセイ又は試験として使用され得；及び／又は、このようなタンパク質干渉又はシグナルを生じさせる傾向を減少させるようにＩＳＶの改変又は改善をガイドするのに使用され得るアッセイ又は試験として使用され得る；－このようなタンパク質干渉又はこ
