FUNCTIONAL INTERLEUKIN-2 RECEPTORS ON INTESTINAL EPITHELIAL-CELLS

The presence of receptors for the cytokine IL-2 was assessed in the IE C-6 cell line established from normal rat crypt epithelium and primary intestinal epithelial cells. I-125-IL-2 was found to specifically bin d to subconfluent IEC-6 cells. Maximal binding was observed within 30 min after addition of the ligand; binding could be inhibited by excess unlabeled IL-2 or addition of antibody to the IL-2 receptor. Both int ermediate and low affinity receptors with approximate K(d) of 10 and 1 00 pM, respectively were present. Kinetic analysis were consistent wit h the results of Western blot analysis using an antisera to the 75-kD IL-2 receptor beta chain. IL-2 receptors appeared to be functional; ad dition of IL-2 led to modulation of proliferation with initial stimula tion at 24 h followed by inhibition at 48 h. This effect could be bloc ked by addition of antibody to the IL-2 receptor beta chain. IL-2 trea tment could be shown to enhance expression (range = 4- to 50-fold stim ulation) of TGF-beta, as well as the lectin protein mac-2, in IEC-6 ce lls. The relevance of observations in the IEC-6 cell line to intestina l mucosa in vivo was supported by the demonstration of a gradient of e xpression of the IL-2 receptor in primary rat intestinal epithelial ce lls by Western blot analysis. In addition, mRNA for the IL-2 receptor- beta chain was demonstrated by Northern blot analysis using mRNA from primary rat intestinal epithelial cells depleted of detectable contami nating intraepithelial lymphocytes by two cycles of fractionation on P ercoll gradients. Collectively, these observations suggest that the ra nge of cellular targets of the putative lymphokine IL-2 is broader tha n appreciated, and IL-2 may serve to integrate epithelial and lymphocy te responses in the intestinal mucosa.