Final answer:
While the provided information does not directly answer when L1 cell surface is cleaved in T98G cells, related biological mechanisms suggest cleavage could occur due to immune cell activity or the action of enzymes like MMPs, associated with tumor progression.
Step-by-step explanation:
From the context provided, it appears that L1 cell surface expression could be related to the study of cancerous cells or viruses interacting with the host's cell machinery. The information mentions T98G cells, which are a line of human glioblastoma cells, but does not provide direct data regarding cell surface L1 cleavage. However, by exploring related scenarios, such as the interaction of cytotoxic T cells with MHC I molecules on infected cells, we can infer that L1 cell surface cleavage might occur under conditions where enzymes like matrix metalloproteinases (MMPs) are up-regulated, which is commonly seen in tumor progression.
Furthermore, the action of cytotoxic T cells producing granzymes and perforins when encountering an MHC I-epitope complex suggests mechanisms where cell surface molecules, potentially including L1, might be enzymatically cleaved. In the case of T98G cells, or tumor cells in general, the modified expression of MHC I molecules and the presence of active inhibitors from viruses could lead to vulnerabilities on the cell surface, which may involve the cleavage of L1 under certain circumstances, such as immune cell attack or enzyme action.