Peanut agglutinin (PNA): binding and stimulation of bovine intestinal and peripheral blood leukocytes

The use of peanut agglutinin (PNA) as a reliable marker for bovine T lymphocytes as well as its in vitro lymphoblastogenic capacity were investigated and compared to those of concanavalin-A (ConA). The binding ability of fluorescein isothiocyanate conjugated PNA (FITC-PNA) and FITC-ConA to bovine leukocytes isolated from peripheral blood (PBL) as well as from the intraepithelium (IEL), lamina propria (LPL) and Peyer's patches (PPL) of the small intestinal mucosa of five normal adult cows (n = 5) was analyzed using laser flow cytometry (LFC) and fluorescence microscopy. Monoclonal antibodies (mAb) specific for bovine T cells (B26A), B cells (PIg45A), "null" cells (B7A1) and monocytes/granulocytes (DH59B) were employed to determine the phenotype of the cell lineage(s) expressing PNA surface receptor(s). There were no significant variations (P greater than 0.1) in the proportion of PNA-binding cells in PBL (76%), PPL (77%), IEL (79%) and LPL (81%) even though there were significant differences between the percentages of B26A+ T cells in IEL (26%) and LPL (38%) (P less than 0.001) and in PPL (44%) and PBL (57%) (P less than 0.01). These studies clearly indicate that cells other than T cells bind PNA. Although the proportions of PNA-binding cells in enriched PP-B cells (30%) and enriched PP-plastic adherent cells (44%) were significantly lower (P less than 0.001) than those in enriched PP-T cells (95%), the results indicated that a reasonable number of non-T cells can specifically bind FITC-PNA. Additional support was obtained by similar results observed with the equivalent cell subsets from PBL. Using in vitro lymphoblastogenesis, the PNA stimulating capacity significantly varied between the various cell populations (P less than 0.001 between IEL and PBL; and P less than 0.02 between PPL and PBL). In addition, marked differences were observed between the binding ability and stimulating capacity of PNA on each leukocyte population (P less than 0.01 in PBL to P less than 0.001 in IEL). Concanavalin A which bound to approximately 100% of each cell population, revealed significant variation in its mitogenic activity between IEL and PBL (P less than 0.001) but not between LPL and PPL (P greater than 0.1). The finding that PNA can bind to bovine T cells as well as to some B cells, monocytes/macrophages and possibly some granulocytes and "null" cells disputes its reliability as a specific bovine T cell marker. Furthermore, the binding abilities of PNA and ConA to bovine leukocytes are not necessarily correlated to their in vitro mitogenic capacities.