J. Biol. Chem., Vol. 265, Issue 17, 9943-9951, 06, 1990
Heterogeneity in interleukin (IL)-1 receptors expressed on human B cell lines. Differences in the molecular properties of IL-1 alpha and IL-1 beta binding sites
D Benjamin, S Wormsley and SK Dower
Saint Francis Research Institute, University of Oklahoma, Health Sciences Center, Oklahoma City 73190.
IL-1 alpha and IL-1 beta although distantly related at the primary sequence
level, bind to the same Mr 80,000 IL-1 receptor on various cell types.
Several lines of evidence indicate, however, that the IL-1 receptor on B
cells and T cells differ. By binding experiments with 125I-IL-1, marked
heterogeneity in IL-1 receptor binding was observed in 13 of 24 B cell
lines studied. This was classified into three categories: (I) in nine cell
lines, 125I-IL-1 alpha binding revealed high (kD = 10(-10) M) and low
affinity (kD = 10(-8) M) IL-1 alpha receptors, whereas 125I-IL-1 beta
binding showed one class only with intermediate affinity (kD = 10(-9) M);
(II) in three cell lines selective binding with 125I-IL-1 beta was
observed; (III) in one cell line only, 125IL-1 alpha and 125I-IL-1 beta
bind to a single class of IL-1 receptors as has been described for most
cell types. Cross-linking with 125I-IL-1 alpha or 125I-IL-1 beta
demonstrated their specific binding to Mr 80,000 and to Mr 68,000 in cell
lines in categories I and III, whereas for those in category II, binding to
the IL-1 receptor was confined to 125I-IL-1 beta. The expression of two
subsets of IL-1 alpha receptors but only one class of IL-1 beta receptors
was further confirmed in kinetic studies. Internalization at 37 degrees C
demonstrated that only 19% of IL-1 beta was internalized and that binding
with IL-1 alpha was entirely cell surface. Flow cytometry studies showed
that IL-1 alpha and IL-1 beta do not influence B cell surface antigen
expression, suggesting that the ability of IL-1 to influence B cell
proliferation is not mediated via direct binding to the IL-1 receptor only.