In vivo analysis of glial cell phenotypes during a viral demyelinating disease in mice

With the three antibodies used in this study, we have detected four different antigenic phenotypes among the spinal cord glial cells: oligodendrocytes (CNP+ 04+, and CNP+ only) two types of astrocytes (GFAP+ only, and GFAP+ O4+), and the putative O-2A progenitor (O4+, C N P -and GFAP-) (Wolswijk and Noble, 1988) . Cells with these exact same antigenic phenotypes can also be isolated from these spinal cords and cultured (Armstrong, R., V. Friedrich, K. V. Holmes, and M. Dubois-Dalcq, manuscript in preparation). The in vivo morphology of the cells with each anti-genic phenotype is illustrated in Figs. 2 and 3 . The oligodendrocytes displayed CNP staining along the plasmalemma of their cell bodies and processes but not in compact myelin, as described before (Braun et al., 1988 : Trapp et al., 1988 . Thus, of the myelin sheaths, only the outer and inner cytoplasmic loops were stained (Fig. 2 b) . Most oligodendrocytes also bound 04 within the perikaryal cytoplasm (Fig. 2, filled arrow) . As expected, more CNP+ 04+ oligodendrocytes were detected in the white than grey matter. Interestingly, a few cells which only reacted with CNP antibody were present in the grey matter, mostly in the dorsal horn. The GFAP antiserum showed intense filament staining in cytoplasmic bundles, both in cell bodies and in processes, as described (Levine and Goldman, 1988) . Many cells were stained only for GFAP; these are thought to represent type 1 astrocytes (Raft et al., 1983a) . In addition we found numerous astrocytes which stained for 04 in addition to GFAE We identify these as type 2 astrocytes (Raft et al., 1983a) (Fig. 2 , c and d and Fig. 3, c and d) . 04 staining was distributed in these cells as fine cytoplasm granules often prominent in regions of intense GFAP staining. Finally, we found 04+ C N P -GFAP-putative progenitors with a shape similar to that of oligodendrocytes. These cells were smaller than oligodendrocytes and their processes could never be followed to myelin sheaths (Fig. 3, bottom) . They were very rare in normal animals (average one per section and present only in the white matter [ Fig. 3]) .