INHIBITION OF CD4-LYMPHOCYTE BINDING TO FIBRONECTIN AND IMMUNE-CELL ACCUMULATION IN INFLAMMATORY SITES BY NONPEPTIDIC MIMETICS OF ARG-GLY-ASP( T)

The Arg-Gly-Asp (RGD) cell adhesion motif has been demonstrated in var ious studies to play a pivotal role in leucocyte and platelet interact ions with plasma and extracellular matrix (ECM) glycoproteins. The rec ognition of the RGD sequence is mediated by heterodimeric receptors de signated integrins of the beta(1) subfamily, expressed on distinct cel l types, including T lymphocytes. We have recently shown that flexible non-peptidic mimetics of RGD, in which the two ionic side groups were separated by a linear spacer of 11 atoms, bound specifically to the p latelet integrin alpha(IIb)beta(3), and inhibited T cell-mediated immu ne responses. The present study was designed to (i) further characteri ze the structural requirements for RGD interactions with CD4(+) T cell s, and (ii) examine the mechanisms by which the RGD mimetics interfere with immune cell reactivity in vivo. We now report that freezing the conformational degrees of freedom in the spacer chain, which fixes the relative orientation of the guanidinium and carboxylate side groups i n a favourable manner, results in a higher level of inhibition of T ce ll binding to immobilized fibronectin, an RGD-containing ECM glycoprot ein. In vivo, treatment of mice with relatively low doses of the RGD m imetics, but not the RGD peptide, inhibited the elicitation of an adop tively transferred DTH reaction. This inhibition was achieved by direc t impairment of the ability of antigen-primed lymph node cells to migr ate and accumulate in inflammatory sites. Hence, we suggest that the d esign and production of non-peptidic mimetics of RGD offers a novel ap proach to study defined parameters related to the structure-function r equirements of small adhesion epitopes. Furthermore, this approach cou ld be used therapeutically to inhibit pathological processes which dep end on RGD recognition.