Ultrastructural immunocytochemical localization of lysozyme in human monocytes and macrophages

Abstract

In order to investigate the mechanism of synthesis and secretion of lysozyme (LZ) by human mononuclear phagocytes, the ultrastructural localization of LZ was studied by a pre-embedding direct immunoperoxidase method. Blood monocytes showed a reaction product for LZ in cytoplasmic granules, whereas cultured monocytes showed the reaction product in phagosomes as well as granules at 5 h of culture and in numerous large granules at 3 days of culture. In Kupffer cells, LZ was present in cytoplasmic granules, vacuoles and phagosomes. Some Kupffer cells showed a positive reaction for LZ in the rough endoplasmic reticulum, perinuclear cisterna and Golgi apparatus. Macrophages in the lymph nodes contained LZ in cytoplasmic granules. Bone marrow macrophages contained numerous phagosomes with electron-dense degradation products of erythrocytes, but the reaction product for LZ could not be clearly identified. The present study demonstrated that LZ is present in the granules of human mononuclear phagocytes and released into phagosomes. An in-vitro culture study, furthermore, demonstrated that macrophages produce LZ-containing large granules distinct from those of monocytes. However, findings that indicate the synthesis and secretion of LZ by cultured monocytes, as suggested previously by other investigators, were not observed in this study.

Genes associated with the tumour microenvironment are differentially expressed in cured versus primary chemotherapy‐refractory diffuse large B‐cell lymphoma

“…Immunohistochemical analyses revealed overexpression of lysozyme, Cathepsin D, UPAR, STAT 1 and galectin 3 in tumours from the cured cohort. Their localization was predominantly in non-tumour cells, mainly macrophages, well in accordance with several other reports (Imort et al, 1983;Miyauchi et al, 1985;Pyke et al, 1993;Sano et al, 2003;Alvaro et al, 2006a). Some of these proteins have been connected to local aggressiveness and adverse prognosis in solid tumours, e.g.…”

Nod2 sensing of lysozyme-digested peptidoglycan promotes macrophage recruitment and clearance of S. pneumoniae colonization in mice

“…Lysozyme hydrolyzes the β-1,4 glycosidic bond between the C1 carbon of N-acetyl muramic acid (MurNAc) and the C4 carbon of N-acetylglucosamine (GlcNAc) residues of the peptidoglycan backbone. Mice have two isoforms of lysozyme: LysM, which is secreted by the epithelium and expressed within phagosomes of myelomonocytic cells such as macrophages and neutrophils (24,25); and LysP, which is expressed by Paneth cells of the small intestine. Because of the abundance of lysozyme on host surfaces, many mucosal pathogens have acquired resistance to lysozyme-mediated degradation by modifying residues of their peptidoglycan backbone (26).…”

Phagocytes Containing a Disease-Promoting Toll-Like Receptor/Nod Ligand Are Present in the Brain during Demyelinating Disease in Primates

“…73 In the CNS of MS patients and EAE-affected monkeys, one might expect many lysozyme-expressing cells, because infiltrates contain many phagocytosing cells and lysozyme is known to be present within granules of phagocytes. [21][22][23] However, in this study, we could not detect lysozyme-containing cells in infiltrates or in the parenchyma of MS brain tissue. Occasional intravascular cells containing lysozyme were found in nondemented controls, in MS and in rhesus monkey EAE brain tissue, which is in agreement with previous findings in MS brain tissue.…”

“…PGN is digested by enzymes with different substrate specificities of which lysozyme and N-acetylmuramyl-L-alanine amidase (NAMLAA) are the best characterized. Lysozyme is present in granules of phagocytes [21][22][23] and partially degrades PGN by hydrolyzing the bond between GlcNAc and MurNAc, resulting in solubilized PGN. We have previously identified and functionally characterized NAMLAA, 24 -27 which was recently shown to be identical to the PGN recognition protein long form (PGRP-L), 28 -30 NAMLAA is expressed by neutrophilic granulocytes but not by monocytes and resting macrophages under normal conditions.…”