Ultrastructural identification of acid complex carbohydrate in cytoplasmic granules of normal and leukaemic human monocytes.

Complex carbohydrate in granules of monocytes was compared with that in granules of neutrophils by ultrastructural cytochemical methods. The acid mucosubstance in granules of both cell types stained with dialysed iron after brief fixation with dilute glutaraldehyde, but that in monocyte granules differed in failing to stain after stronger fixation. Approximately 10% granules in normal blood monocytes stained with this method, whereas more than 90% of granules in leukaemic monocytes from two of seven patients with acute myelomonocytic leukaemia stained intensely. This difference presumably results from unmasking of acid groups in immature granules or increased synthesis of granule mucosubstance in some leukaemic monocytes. Granules of monocytes differed further from those of neutrophils in failing after either type of fixation to stain with a high iron diamine technique for for demonstration of sulphated mucosubstance. The absence of high iron diamine staining could reflect a lack of sulphate esters in monocyte granule mucosubstance, masking of the sulphate groups by other components, or extraction of the sulphated mucosubstance during specimen processing.