Antigen definition requirements

Cross-reactivity The amount of a similar substance that will cause the same displacement of labelled antigen from the antibody as an arbitrary amount of the antigen. The usual definition is ID50, which is the concentration of cross-reacting material required to displace 50% of labelled hapten from the antibody. 

Batch procedures can be useful as pre-flow enrichment of the cells of interest. They can also be used as alternatives to flow sorting if the cells of interest can be appropriately selected. Flow sorting, although slow, is generally the only alternative if multiple parameters are required to define the cells of interest, if antigen density on the cell surface is low, or if forward or side scattered light is part of the definition of the desired cells. 

The first and very important part of any plan is the exact definition of the aim, as explained in the previous chapter. This is followed by a list or sequence of major tasks or sections which each must be accomplished in order to achieve the aim. Since these major sections each define critical steps of the project, success criteria or objectives for each of these must be described and agreed. These objectives should specifically address known or potential difficulties (in our example the purity of antigen that is needed, the required test systems, etc.) and should be defined as exactly as possible at this stage and updated when necessary. The definition of objectives requires a reasonable knowledge of the subject and should thus be discussed and agreed with the specialists in these fields and with those who have to meet these objectives. 

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