Methods of identifying and using FAM150A agents, FAM150B agents, and FAM150 antagonists are provided. Methods of identifying and using LTK agonists (including LTK agonist antibodies, FAM150A agents, and FAM150B agents) and FAM150 antagonists are provided. Such methods include, but are not limited to, methods of treating cancer, methods of treating immune disorders such as autoimmune diseases, and methods of treating neurodegenerative diseases.