Title: “Circulating phagocytic cells”
Description: Electron microscopy, a set of the ultrastuctural features of different types of phagocytic cells.
(A): Circulating monocyte with phagocytized latex particles (peripheral blood, human).
(B): Normal circulating monocyte (peripheral blood, human).
(C): Circulating monocyte-derived macrophage (peripheral blood, human) with phagocytized bacteria (Staphylococcus aureus).
(D): Interdigitating cell in a periarterial lymphatic sheath (PALS in spleen, mouse).
Keywords/Mesh: blood, bone marrow, monocyte, macrophage, antigen-presenting cell, dendritic cell, interdigitating cell, lysosome, phagocytosis, histology, electron microscopy, POJA collection
Top left side (A): Circulating monocyte with phagocytized latex particles (peripheral blood, human). The nucleus is large and with a long small indentation. Close to the nucleus several individually internalized electron-light latex particles (with a dense core) in phagosomes (1). at (3) small electron-dense lysosomal granules. At (2) a phagolysosome containing lysosomes and a latex particle. Outside the cell remnants of latex particles.
Top right side (B): Normal circulating monocyte (peripheral blood, human).
Inset shows light microscopy; note the large nucleus with some indentations, cytoplasmic azurophilic granules are visible. At (4) a light nuclear hof (inset) where Golgi areas are localized. The electron micrograph of the same type of cell shows the large nucleus of this cell (diameter of 12-20 mm) twice sectioned. Golgi areas (4), a few profiles of rough endoplasmic reticulum and many free ribosomes are present. There are many mitochondria as well as small-sized light vesicles. The cytoplasm contains scattered homogeneous electron-dense lysosomal granules (5) (primary or azurophilic granules with acid phosphatase, arylsulfatase) in variable amounts and sizes. Thin filopodia reflect the ameboid movement (note several small subplasmalemmal clefts) and phagocytic ability.
Bottom left side (C): Circulating monocyte-derived macrophage (peripheral blood, human) with phagocytized bacteria (Staphylococcus aureus). Upon incubation of these macrophages with a bacterial suspension the microbes are ingested within phagosomes (6). The bacteria are found in various stages of digestion. Note larger lysosomal structures (7), fat droplets (8) and large electron-lucent vacuoles (9) in the cytoplasm. Several long filopodia reflect the motile and stimulated cell containing a vast amount of bacterial cell bodies.
Bottom right side (D): Interdigitating cell in a periarterial lymphatic sheath (PALS in spleen, mouse). It is a stellate cell with blunt processes (11) that extend between the surrounding lymphocytes (1). Several electron-dense lysosomal structures (2), endocytotic invaginations of the peripheral surface (10) resulting in numerous small electron-light and -dense tubulovesicular profiles are present in the cytoplasm. Golgi areas and a moderate amount of mitochondria and short profiles of rough endoplasmic reticulum are shown perinuclearly.
Background: Monocytes derive from monoblasts in the bone marrow, circulate in the bloodstream for 8-24 hours, and then migrate into tissues, and can remain active for months and probably years. The cells can either differentiate into tissue-macrophages or into antigen-presenting cells (APC´s). They can also be active in antibody-dependent cell-mediated cytoxicity reactions (ADCC). Depending on their activity and differention status these cells display receptors for complement factors, antibodies and chemotactic factors. They can also generate several interleukins.
Dendritic antigen-presenting cells (APC’s), however, internalize exogeneous antigens in the microenvironment of tissues and organs, process and present these processed antigens via binding in the MHC-grooves to lymphocytes.