FACS analysis of MHC expression in neurospheres. Cells were stained by indirect immunofluorescence and levels of expression were analysed by flow cytometry as described in M&M. A: Time course comparison of staining levels attained with MRC OX-18 (diamonds), which stains both class Ia and Ib molecules, or with F16.4.4 (circles) which stains only class Ia molecules. Days of successive passages are indicated by P1, P2, P3. Similar results were obtained in two other experiments. B: FACS profile of cells having aggregated as neurospheres after 48 h of culture. C: FACS profile of the CRNK cell line. For all experiments, both antibodies were used at saturating concentrations.