Inhibition of lymphocyte activation with anti-transferrin receptor Mabs: a comparison of three reagents and further studies of their range of effects and mechanism of action.

Prior work has suggested that Mabs against the transferrin receptor (ATRAs) may function as selective inhibitors of lymphocyte activation and that T cell activation protocols may be more sensitive to ATRA-mediated inhibition than B cell activation protocols. New side-by-side functional comparisons of three ATRAs are presented. When these studies are considered with our prior work they demonstrate unambiguously that although one particular IgG ATRA consistently fails to inhibit LPS responses and although IgM ATRAs may be slightly more effective inhibitors than IgG ATRAs, ATRAs as a class consistently appear to abolish the MLR at submicrogram concentrations, essentially eliminate cytotoxic cell generation at concentrations between 1 and 5 micrograms/ml, and produce no more than about 50% inhibition of LPS responses at concentrations as high as 25 micrograms/ml. Therefore, an even stronger case can now be made for the idea that lymphocyte subsets differ in their dependence on transferrin receptor function during activation. This, in turn, makes an even stronger case for the idea that lymphocyte subsets differ in fundamental aspects of the management of their iron economies. New studies also show that IgG ATRAs appear to function by causing down-modulation of surface expression of the transferrin receptor in normal lymphocytes in a manner similar to that previously shown for tumor cells. It is clear that a sophisticated model will ultimately be required to account for all of the data arising from studies with ATRAs, and a new attempt at a more detailed construct is presented.