how can we detect the rate of B-cell replication?

the method by which the rate of cell cycle can be detected. The easiest method is to synchronize the cells and later label them beside a quantitative membrane-binding dye (such as CFSE), the intensity of which would be reduced by two with respectively cell division (the daughter cells will inherit partially of the mother cell's membrane each). Then you analyse cells by flow cytometry contained by time course and see when most cells see their dye content.
You can also use a DNA-binding dye (such as PI) and measure the DNA content of your cell in time course. The DNA content will increase over time and afterwards drop back to a minimum, which would tight that the cells enter the next cell cycle. The disadvantage of this method is, however, that you hold to take probes normally enough as the second and subsequent cell cycles will be indistinguishable - and you can contained by theory miss the second one.
Measuring cell cycle rates within an unsynchronised population is done technically in a similar instrument, but will require some mathematics, a so-called precursor-product relationship analysis. Using this method and radiolabeled glucose, it have even been possible to weigh the cell cycle rate of T cells within humans (as described in the dissertation cited below)!
try