Effect of Lipopolysaccharide on the Morphology and Integrin Immunoreactivity of Ramified Microglia in the Mouse Brain and in Cell Culture

• Published in: Experimental neurology Vol. 168; no. 1; pp. 32 - 46
• Main Authors: Kloss, Christian U.A., Bohatschek, Marion, Kreutzberg, Georg W., Raivich, Gennadij
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.03.2001; Elsevier
• Subjects: Animals; Antigens, CD - analysis; Antigens, Differentiation - analysis; Astrocytes - cytology; Astrocytes - physiology; Bacterial diseases; Bacterial diseases of the nervous system. Bacterial myositis; Biological and medical sciences; Brain - cytology; Brain - drug effects; Brain - pathology; Brain Stem - drug effects; Brain Stem - pathology; Cells, Cultured; Cerebellum - drug effects; Cerebellum - pathology; coculture; Coculture Techniques; Human bacterial diseases; Infectious diseases; Inflammation; Integrin alpha4; Integrin alpha4beta1; Integrin alpha5; Integrin alpha6beta1; Integrin beta1 - analysis; Integrins - analysis; Lipopolysaccharides - toxicity; Male; Medical sciences; Mice; Mice, Inbred C57BL; Microglia - cytology; Microglia - drug effects; Microglia - pathology; neuroglia; Receptors, Fibronectin - analysis; Receptors, Lymphocyte Homing - analysis; sepsis; VLA; VLA; coculture; neuroglia; inflammation; mice; sepsis; Cell culture; Nervous system diseases; Immune response; Rodentia; Cell adhesion molecule; Endotoxin; In vitro; Cerebral disorder; Microglia; Infection; In vivo; Vertebrata; Mammalia; Integrin; Mouse; Animal; Morphology; Central nervous system disease; Lipopolysaccharide; Brain (vertebrata)
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1006/exnr.2000.7575

Microglial cells form the first line of defense in brain infection. They are related to monocytes and macrophages and can be readily activated by cell wall components of bacteria such as lipopolysaccharides (LPS). In the present study, we explored the effect of this endotoxin in mouse on the morphology of microglia and their immunoreactivity for the integrin family of cell adhesion molecules in vitro and in vivo. Subcutaneous injection of LPS led to a dose-dependent activation of αMβ2-positive microglia, with a saturating effect at 1 μg LPS in the blood–brain barrier deficient area postrema, at 10 μg in the directly adjacent tissue, and at 100 μg throughout the brainstem and cerebellum. Morphologically, this activation was characterized by the swelling of the microglial cell body, a thickening of the proximal processes, and a reduction in distal ramification. Microglial immunoreactivity for the integrins α4β1, α5β1, α6β1, and αMβ2 was strongly increased. In vitro, ramified microglia were obtained using a coculture on top of a confluent astrocyte monolayer. Two days exposure to LPS resulted in a morphological activation of the cultured cells with an increase of the integrin immunoreactivity for α5 (5.7-fold), α4 (3.1-fold), β1 (2.3-fold), and αM (1.5-fold), and a decrease in the α6-staining intensity by 39%. Even a sublethal dose of LPS (3 mg in vivo and 500 μg/ml in vitro, respectively) did not induce the phagocyte-associated integrin αXβ2 (CD11c/CD18, p150,95) and did not lead to a morphological transformation of the ramified microglia into phagocytes.