HETEROGENEITY OF ANTIGEN EXPRESSION AND LECTIN LABELING ON MICROGLIALCELLS IN THE OLFACTORY-BULB OF ADULT-RATS

Microglia in different layers of the rat olfactory bulb expressed a va riety of membrane antigens except for CD4 (OX-35). Bulb microglial cel ls bearing complement receptor type 3 (OX-42) were ubiquitous and thei r immunoreactivity varied considerably in different bulb layers. Altho ugh very few in number, labeled microglia in all layers also expressed major histocompatibility complex class I antigen (OX-18), leukocyte c ommon antigen (OX-1) and unknown macrophage antigen (ED-2). The latter was localized in cells distributed almost exclusively in the perivasc ular spaces. The immunoreactivity of ED-1, an unknown cytoplasmic or l ysosomal membrane antigen in macrophages, was localized in labeled mic roglia which were concentrated mainly in the granule cell layer and pe riglomerular zone of the bulb. A variable number of microglial cells w ere stained with OX-6 (major histocompatibility complex class II antig en) and they were located predominantly in the periglomerular zone and at the junction between the granule cell layer and the subependymal l ayer. Ultrastructural study using GSA I-B4 lectin labeling showed that microglia in different layers of the bulb exhibited similar labeling patterns in their subcellular structures. A remarkable feature was the occurrence of some microglia in the olfactory nerve layer, subependym al layer and granule cell layer adjacent to the subependymal layer in which the cells showed intense lectin labeling at their Golgi apparatu s, a feature which was absent in microglia of other bulb layers. Prese nt results showed the regional differences in microglial antigen expre ssions and lectin labeling within the olfactory bulb. It is therefore suggested that the cells subserve very different specific functions de pending on their ambient microenvironments. The heterogeneity of micro glial functions in the olfactory bulb may be related to the progressiv e regeneration and degeneration of its containing neurons. (C) 1997 El sevier Science Ireland Ltd.