Ultrastructural localization of lactoferrin in the granules other than typical secondary granules of human neutrophils.

In neutrophils, lactoferrin is generally considered to be contained in secondary granules in which myeloperoxidase is lacking. However, it remains obscure whether lactoferrin is also contained in other organelles. We investigated subcellular localization of lactoferrin in human neutrophils by different immunoelectron microscopic methods. Lactoferrin was detected in secondary granules, and also in some large granules which could be distinguished from secondary granules based on their size and shape. These findings seem to indicate that the lactoferrin-positive large granules might represent primary ones or belong to another type of granules other than primary and secondary ones.