Coronavirus induction of class I major histocompatibility complex expression in murine astrocytes is virus strain specific

The inability of JHMV to stimulate class I expression in C57BL/6 astrocytes in the current studies was not reported for astrocytes from BALB/c, CXJ-8, SJL, and B10.S mice by Joseph et al. (69) . In these experiments, JHMV infection at an m.o.i, of 0.1 was followed by a two-to threefold increase in the expression of H-2K molecules, measured by FACS | analyses, but astrocytes from C57BL/6 mice were not tested. The disparity in our findings may again reflect differences in the regulation of class I expression that are mouse strain specific. However, it is also possible that the disparity may be due to the cellular composition of the astrocyte cultures used for infection. In their report, Joseph et al. (69) , did not indicate whether or not they purified the astrocytes from mixed glial cell cultures. In our hands, mixed glial cells that have not been subjected to mechanical shaking for purification of astrocytes show up to 30% contamination by microglia, or cells staining for macrophage/monocyte surface antigens (data not shown). Microglial cells readily express class I molecules both in vivo and in vitro (70) (71) (72) , and so might be expected to express class I after JHMV infection. The cultures used in our experiments routinely show 95% or greater purity, containing 2-4% microglial cells, and "~50% express class I after A59 infection. Thus, class I expression in these cultures occurs primarily in astrocytes, with little, if any contribution by microglia. Finally, it should also be mentioned that class I expression in astrocytes, like that in endothelial cells, does not appear to be linked to susceptibility to JHMV-induced CNS disease, since both BALB/c and C57BL/6 develop encephalitis and demyelination in spite of their differences in class I inducibility after JHMV infection. In addition, astrocytes from SJL mice express class I after JHMV infection in spite of being resistant to CNS disease.