ROCK and actin polymerization inhibition differentially affects Ag presentation by CD1d and MHC class II. A, L-CD1-DR4 cells were pulsed with vehicle or HSA in the presence or absence of the ROCK-specific inhibitor Y-27632. The cells were then fixed and co-cultured with the HLA-DR4-specific 17.9 T cell hybridoma (left panel) for analysis of Ag presentation by MHC class II, or with the NKT cell hybridoma N37-1A12 for measuring CD1d-mediated Ag presentation (right panel); *, P < 0.05; **, P < 0.01 as compared to mock-treated. This result is representative of two independent experiments. B, HSA was added to L-CD1d-DR4 cells before, after, or simultaneously with cytochalasin D. The cells were then fixed and co-cultured with the 17.9 T cell hybridoma. IL-2 production was measured by ELISA. This result is representative of two independent experiments.