Channel shift in a flow cytometry crossmatch is determined by examining which histogram?

In flow cytometry, a channel shift refers to a change in the fluorescence signal of a particular marker when comparing different conditions or samples. This is often assessed by analyzing histograms that represent the distribution of fluorescently labeled cells.

In the context of a crossmatch, which is performed to assess potential immunological compatibility between a donor and recipient, one of the key parameters analyzed is the presence of specific surface markers that indicate cell activation or the potential for an immune response. The comparison of FITC (fluorescein isothiocyanate) labeled cells against cell number provides vital information on how many cells express a given marker.

Choosing to examine the FITC versus cell number histogram specifically allows for the identification of shifts in fluorescence intensity, which may indicate a change in the activation state of the cells. This is crucial for interpreting the results of a crossmatch, particularly in determining the likelihood of an alloimmune response.

The other options pertain to different combinations of cell markers or scatter properties that do not specifically relate to the fluorescence shifts needed to assess channel shifts in the context of crossmatching and compatibility testing. For example, while FSC (forward scatter) versus SSC (side scatter) gives insights into cell size and granularity, it does not provide