Inhibition of lymphocyte stimulation by shift reagents

Lanthanide shift reagents have opened a new avenue in the study of membrane biochemistry, but their stabilities and biological reactivities remain questionable. We present evidence that shift reagents are not biologically inert, and that they exhibit the ability to inhibit stimulation of human peripheral lymphocytes at commonly used concentrations. A survey of various mitogens yielded no shift reagent-resistant modes of stimulation, and a survey of various shift reagents yielded no effective and nontoxic alternatives. Involvement of calcium-regulating mechanisms was not apparent. The assumption that lanthanide shift reagents used in NMR studies are nondestructive and physiologically innocuous is thus shown to be unwarranted.