THE EFFECT OF IL-4 ON ANTIGEN EXPRESSION - A COMPARISON OF FLUORESCENCE INTENSITY AND ANTIGEN DENSITY

We have compared the membrane expression of MHC class II antigen and I g on murine splenic B lymphocytes by two flow cytometric methods, The first method, commonly used, determined the mean immunofluorescence in tensity; the second measured antigen density as a ratio of mean fluore scence intensity to cell volume. The data generated by the two methods allow for different interpretations of antigen density in comparison to antigen expression, By mean fluorescence intensity, activated B lym phocytes expressed more MHC class II antigen and membrane Ig than did resting B cells. However, resting B cells had the same density of MHC class II antigen and membrane Ig as activated B cells, Next we examine d the effect of IL-4 on antigen expression by the two methods, We foun d that although IL-4 increased the mean fluorescence intensity and den sity of MHC class II and membrane Ig on each B cell population, the de nsity of expression of membrane Ig tended to be greater on the resting B cells than on the activated, while the density of MHC class II anti gen was essentially the same on each of the IL-4 treated B cell popula tions.