DIFFERENTIAL BINDING OF 2 CHICKEN BETA-GALACTOSIDE-SPECIFIC LECTINS TO HOMOLOGOUS LYMPHOCYTE SUBPOPULATIONS AND EVIDENCE FOR INHIBITOR ACTIVITY OF THE DIMERIC LECTIN ON STIMULATED T-CELLS

Plant lectins can be potent modulators of vertebrate immune functions. Biochemical characterization of lectins from animal tissues enables t he determination of whether these endogenous activities display a comp arable immunological potency. Focusing on chicken beta-galactoside-bin ding lectins, the monomeric intestinal (CL-14) and the dimeric liver l ectin (CL-16) were purified and the lack of cross-contamination was as certained. In very close agreement with the molecular masses of 14,974 and 14,976 calculated on the basis of the available sequence data (Y. Sakakura ct al., J. Biol. Chem. 265, 21573-21579, 1990), electrospray mass spectrometric analysis yielded values of 14,969 (CL-14) and 14,9 72 (CL-16), the reasons for the deviation in gel electrophoretic behav ior being unclear. Solid-phase assays with immobilized lactosylated po ly-L-lysine demonstrated a comparatively lower affinity and higher ext ent of binding at saturation for the monomeric lectin than for the dim eric protein, whose properties were similar to those of an immunomodul atory plant lectin. Flow cytometry revealed homogeneous and strong bin ding of the dimeric lectin within the chicken peripheral blood lymphoc yte population, whereas the monomeric lectin stained two subpopulation s at different intensities. Two-color flow cytometry disclosed prefere ntial binding of this lectin to B cells. When a B cell line was employ ed for determination of affinity constants and extents of binding at s aturation, qualitatively comparable parameters to those for the solid- phase assays were obtained. The similar profile of lectin-binding glyc oproteins in blots of cellular extracts underscored that accessibility to ligands, not qualitatively different ligand display, may explain t he differences for the cell line. At up to a concentration of 10 mu g/ ml of the lectins no stimulation of [H-3]thymidine incorporation was s een for blood and spleen cell populations. However, the dimeric lectin reduced stimulation of cells that were responsive to an anti-TcR(2) a ntibody. Thus, this lectin can apparently exhibit inhibitory activity to this kind of T cell activation in vitro. (C) 1995 Academic Press, I nc.