TABLE 1.

Function, resident cell types and clinical relevance of the major identified LROs

LRO	Function	Resident cell type	Major clinical features when defective
Melanosome	Intracellular melanin biosynthesis and storage. Melanin transfer to keratinocytes.	Melanocytes, iris and retinal pigment epithelial cells	Ocular and cutaneous hypopigmentation
Delta granule	Storage of small molecules, released for blood coagulation.	Platelets, megakaryocytes	Bleeding diathesis
Lytic granule	Intracellular degradation of macromolecules. Upon release, extracellular destruction of virally infected or cancerous target cells.	Cytotoxic T lymphocytes, natural killer cells	Immune deficiency, viral infections
Azurophil granule	Storage of hydrolytic enzymes, destruction of phagocytosed bacteria. Upon secretion, support of various pathological processes, including inflammation.	Neutrophils, eosinophils	Neutropenia, immune deficiency, bacterial infections
Basophil granule	Storage of histamine, serotonin, heparin, IL-4, and lysosomal proteases. Released for regulation of inflammation.	Basophils, mast cells	Immune deficiency, allergies
Lamellar body	Storage and secretion of surfactants for lung function.	Lung type II epithelial cells	Interstitial lung disease, lung inflammation and fibrosis
MHC class II compartment	Intracellular processing and incorporation of antigens into cell membranes.	B lymphocytes, macrophages, dendritic cells, other antigen presenting cells	Immune deficiency
Neuromelanin granule	Storage of the insoluble pigment neuromelanin which binds iron.	Catecholaminergic neurons of the brainstem	Unknown
Ruffled border	Bone resorption and remodeling. Storage, activation and/or release of acid hydrolases.	Osteoclasts	Osteopetrosis
Weibel-Palade body	Storage and regulated release of hemostatic and pro-inflammatory factors (von Willebrand Factor, P-selectin)	Endothelial cells	Bleeding diathesis