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Diversity amongst the microglia in growing and regenerating fish CNS: Immunohistochemical characterization using FL. 1, an anti‐macrophage monoclonal antibody
Author(s) -
Dowding Alan J.,
Maggs Alison,
Scholes John
Publication year - 1991
Publication title -
glia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.954
H-Index - 164
eISSN - 1098-1136
pISSN - 0894-1491
DOI - 10.1002/glia.440040403
Subject(s) - microglia , biology , macrophage , monoclonal antibody , immunocytochemistry , immunohistochemistry , pathology , neuroglia , central nervous system , microbiology and biotechnology , ependymal cell , antibody , immunology , neuroscience , inflammation , biochemistry , medicine , in vitro , endocrinology
We have immunohistochemically characterized the forms and distribution of microglia—the macrophages of the CNS—in fish, using a new monoclonal antibody (mAb), FL.1. This mAb specifically reacts with resident macrophages throughout the body in Oreochromine fish, including Kupffer cells, gut‐associated myeloid cells, and peritoneal macrophages, as well as with microglia, but circulating monocytes are not labelled with FL.1. The FL.1‐epitope, which is lost following treatment with reducing agents, has an extracellular location and is associated with three integral membrane glycoprotein variants. FL.1‐staining shows that microglia are extremely abundant throughout the fish CNS. For example, they comprise a third of the glia in the optic nerve, and 30% of all cells, including neurons, in the spinal cord, i.e., fish have about tenfold more microglia than mammals. Two forms of FL.1‐positive microglia are predominant in fish, one resembling their mammalian counterparts, but less ramified, and the other comprising smaller rounded cells with very little cytoplasm, which are most numerous in the ependymal region of the optic tectum. Apart from the conventional microglia, the optic nerves also contain large lipid‐laden macrophages which comprise a third form of FL.1‐positive cell in the CNS. Fish optic nerves contain astrocytes of a distinct type which form reticular networks, but lack connections to capillaries (Maggs and Scholes, J. Neurosci. 1990;10:1600–1614). The co‐distribution of foamy macrophages may have a metabolic role that is performed by ordinary astrocytes elsewhere in the CNS. An antiserum against the β 2 subunit of the human leukocyte integrins (Kishimoto et al., Cell 1987a; 50:193–202) was found selectively to recognize the foamy macrophages in Oreochromis . Following lesion to the optic nerve, FL.1‐labelling shows that microglia proliferate throughout the visual pathway. In the optic tectum, the additional FL.1‐positive cells are concentrated in the vicinity of degenerating retinal axons and their terminals. Most of the microglia in the injured optic nerve have amoeboid morphologies, and the foamy macrophages become depleted.