Fig. 6.

Astrocytes as antigen-presenting cells. Astrocytes cultured in vitro for 72 h in the absence (a, c) or presence of IFN-γ (b, d) maintain GFAP (red) and AQP-4 (green) expression. None of the untreated (c) and approximately 10% of the IFN-γ treated astrocytes (d) express MHC class II products (OX-6 staining red). e Presentation of exogenous antigens by IFN-γ treated astrocytes. When these cells were cocultured with AQP-4_207–232-specific T cells in the absence of externally added antigens (0), or in the presence of AQP-4_54–71 representing AQP-4 loop A (A), AQP-4_137–157 representing AQP-4 loop C (C), AQP-4_207–232 representing AQP-4 loop E (E), AQP-4_277–322 representing the C-terminal, intracellular domain of AQP-4 (ic), myelin basic protein (MBP) as an irrelevant CNS antigen, or concanavalin A (ConA), T cell activation was only detected upon exposure to AQP-4_207–232 and in response to ConA. Shown in this graph are differences in the average counts per minute (Δcpm) obtained from triplicate cultures of T cells challenged with antigens and IFN-γ treated or untreated astrocytes, given as mean ± SD. The graph is representative of two experiments. f No presentation of endogenous AQP-4 peptides by IFN-γ-treated astrocytes. The average cpm (mean ± SD) seen when astrocytes were cocultured in triplicates with AQP-4_207–232-specific T cells in the absence of AQP-4_207–232 (273.3 ± 110.0) is in the range of the sum of the cpm (mean ± SD) of astrocytes alone (131.7 ± 42.7) plus AQP-4_207–232-specific T cells cultured with AQP-4_207–232 only (137.5 ± 27.6; to reveal carryover of antigen-presenting cells in the T cell preparation used) or AQP-4_207–232-specific T cells cultured without antigen (64.3 ± 9.1). The graph is representative of two experiments