Receptors for pea and lentil lectins on human lymphoid cells: demonstration of distinct lectin-defined cell...

Lectins are useful probes for studying cell surface glycoconjugates. Pea (PL) and lentil (LL) lectin each requires for binding a fucosyl- and two alpha-mannosyl residues in core regions of glycopeptides, but differences in outer chain carbohydrates may alter their relative binding affinities. We used binding studies with [125I]-PL and LL and flow cytometry with fluorescein-conjugated (FITC)-PL and -LL to study their interactions with peripheral lymphocytes. Binding of both lectins to lymphocytes was saturable, reversible, and inhibited by alpha-methyl mannose. Scatchard analyses were consistent with two classes of receptors for each lectin. Flow cytometric analyses demonstrated that cell to cell receptor densities varied. Sixty-five percent of lymphocytes bound PL (mean 2 X 10(6) receptors/cell) and 45% bound LL (mean 3 X 10(6) receptors/cell). Competition studies demonstrated mutual inhibition, but flow cytometry revealed persistent FITC-PL or -LL binding depsite 20-fold molar excess of the other lectin. Distributions of receptors for PL and LL on lymphocytes were as follows: 45% of lymphocytes bound both PL and LL; 20% of lymphocytes bound PL alone; 35% of lymphocytes bound neither PL nor LL. Despite similar binding requirements for PL and LL and overlap between their receptors on lymphocytes, there appear to be subsets of receptors specific for each lectin. These results may reflect abilities of PL and LL to discriminate subtle carbohydrate differences on lymphocyte surfaces.