Prednisone in Adults With an Immune-Mediated Subtype of Autism Spectrum Disorder

The goal of this clinical trial is to learn how prednisone affects adults with autism spectrum disorder (ASD). It will also learn about the safety of prednisone. The main questions it aims to answer are: * How does prednisone affect the core features and associated target symptoms of ASD in adults with an immune-mediated subtype of ASD? * Is prednisone safe for autistic adults without causing too many side effects? * Does this study warrant larger trials studying anti-inflammatory drugs in this subject population? Researchers will compare the drug prednisone to a placebo (a look-alike substance that contains no drug) to see how prednisone affects autistic adult males. Participants will: * Visit the clinic 2 times for a screening and baseline visit. * Take prednisone or a placebo every day for 16 weeks. * Visit the clinic 2 times for checkups, tests, questionnaires, and dose changes, and 1 time for a follow-up visit 4 weeks after stopping the study drug. * Provide blood and urine samples for testing up to 4 times. * Complete 8 remote calls every 1-2 weeks for checkups and dose changes. * Keep a diary of the dose and times they take the study drug every day and any symptoms or side effects they experience.