Characterization of caprine microglial cells and in vitro infection with caprine arthritis-encephalitis lentivirus.

BACKGROUND

Similar to human immunodeficiency virus-1 and simian immunodeficiency virus-1, microglial cells in brain tissue are a major cell target for infection with caprine arthritis-encephalitis lentivirus (CAEV) in vivo. These observations have raised interest in the role of microglial cells in the development of lentivirus-induced neurologic lesions. To initiate in vitro studies into the pathogenesis of encephalomyelitis caused by CAEV, we characterized primary cultures of caprine microglia, determined their susceptibility to virus infection, and examined the effect of virus infection on class I and class II major histocompatibility complex antigen expression.

EXPERIMENTAL DESIGN

Microglia were examined as adherent cells in purified cultures and as nonadherent cells in mixed glial cell cultures, which also contained astrocytes and oligodendroglia. The cultured cells were investigated with regard to their phenotype, class I and II major histocompatibility complex antigen expression, and susceptibility to infection with CAEV using light and electron microscopy, enzyme and lectin cytochemistry, immunocytochemistry, flow cytometry, and kinetic analysis of virus replication.

RESULTS

The cultured microglia had a typical macrophage morphology, were actively phagocytic, and expressed macrophage-like markers including non-specific esterase, complement receptor CR3, and Ricinis communis agglutinin-1. Microglia were highly permissive to CAEV infection in vitro as indicated by induction of syncytial cells, formation of lentivirus particles, expression of viral antigens, and release of high titered infectious virus into culture supernatants. CAEV selectively infected microglia in mixed glial cultures but replicated less efficiently than in purified microglial cultures; productive infection of astrocytes or oligodendrocytes was not detected. There was constitutive expression of class I and class II major histocompatibility complex antigens on microglia in purified and mixed cultures that was not altered significantly by CAEV infection alone.

CONCLUSIONS

These observations demonstrated that cultured caprine microglial cells had a macrophage-like phenotype and were highly permissive to productive CAEV infection in vitro. This primary brain culture system is a valuable tool to study lentivirus-microglial interactions in the central nervous system.