Distribution of lectin binding sites in human bone marrow. Identification by use of an ultrastructural postembedding technique.

The purpose of this ultrastructural study was to detect various carbohydrate residues on mature elements of the major human haematopoietic cell lines (granulopoiesis, erythropoiesis and megakaryopoiesis), sinus endothelium and plasma cells under comparable experimental conditions. Marrow specimens were processed according to a modified postembedding technique with Unicryl as embedding resin. A broad panel of 10 digoxigenin (dig)-conjugated lectins was applied for staining and specificity was evaluated by incubation with their corresponding inhibitory sugars. Lectins under study were derived from Canavalia ensiformis (Con A), Triticum vulgare (WGA), Ulex europaeus-I (UEA-I), Baubinia purpurea (BPA), Erythrina cristagalli (ECA), Glycine max (SBA), Helix pomatia (HPA), Arachis hypogaea (PNA), Griffonia simplicifolia-I (GS-I) and its isotype GS-I-B4. As a common feature WGA was shown to be a prominent marker of cytoplasmic membranes, except for plasma cells. On the other hand, Con A turned out to be reactive with the nuclear envelopes in all haematopoietic cells and, additionally, exhibited a strong labelling of the rough endoplasmic reticulum in plasma cells. Granules of eosinophilic granulocytes revealed staining of varying intensity with all lectins; however, inhibition was mostly incomplete. Several lectins (WGA, Con A, UEA, BPA, ECA, SBA and PNA) disclosed a clear cut differentiation of at least two subpopulations of granules in polymorphonuclear leukocytes. UEA-I (H type 2 specific) exhibited a high affinity to cytoplasmic membranes of erythropoietic precursor cells. In keeping with the blood group of our patient (O Rh+) membranes of red blood cells were completely negative with those lectins that are known to exhibit a group A or B specificity (HPA, GS-I-B4). As a remarkable finding the luminal and abluminal surfaces of sinusoidal endothelium revealed a specific reaction with UEA-I. Carbohydrate binding sites on the surface of endothelial cells may play a pivotal role in several functional processes such as cellular adhesion, traffic of mature cell elements across the marrow blood barrier and "homing' of haematopoietic stem cells.