A Study to Evaluate the Efficacy, Safety, Pharmacokinetics (PK), and Pharmacodynamics (PD) of Satralizumab in Participants With Anti-N-methyl-D-aspartic Acid Receptor (NMDAR) or Anti-leucine-rich Glioma-inactivated 1 (LGI1) Encephalitis

Inclusion Criteria: * Reasonable exclusion of tumor or malignancy before baseline visit (randomization) * Onset of AIE symptoms ≤ 9 months before randomization * Meet the definition of "New Onset" or "Incomplete Responder" AIE * For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use adequate contraception during the treatment period and for at least 3 months after the final dose of satralizumab or placebo * For participants enrolled in the extended China enrollment phase at China's sites: participants who are current residents of mainland China, Hong Kong, or Taiwan, and of Chinese ancestry NMDAR AIE Cohort: * Age ≥ 12 years * Diagnosis of probable or definite NMDAR encephalitis LGI1 AIE Cohort * Age ≥ 18 years * Diagnosis of LGI1 encephalitis Exclusion Criteria: * Any untreated teratoma or thymoma at baseline visit (randomization) * History of carcinoma or malignancy, unless deemed cured by adequate treatment with no evidence of recurrence for ≥ 5 years before screening * For participants with NMDAR AIE, history of negative anti-NMDAR antibody in cerebrospinal fluid (CSF) using a cell-based assay within 9 months of symptom onset * Historically known positivity to an intracellular antigen with high cancer association or glutamate decarboxylase 65 (GAD-65) * Historically known positivity to any cell surface neuronal antibodies other than NMDAR and LGI1, in the absence of NMDAR and LGI1 antibody positivity * Conf…