Immune Mechanisms of Antipsychotic Treatment Response

Inclusion Criteria Participants with psychosis symptoms: * Age 18-65 * Currently experiencing psychosis symptoms warranting treatment by secondary care mental health services, as confirmed by a psychiatrist involved in their treatment. * Psychosis symptoms likely to be attributable to a disorder represented by ICD codes F20-F39, in the opinion of the treating clinical team. * Due to start or change to a new regular antipsychotic medication. (Participants who are initiating antipsychotic treatment for the first time, transitioning to a different antipsychotic medication, or resuming a formerly prescribed antipsychotic medication that was discontinued for a minimum of two weeks may be recruited.) Control Participants * Age 18-65 * No active autoimmune disorder. * No history of psychosis symptoms. Exclusion Criteria Participants with psychosis symptoms: * Unacceptable risk of harm to participant or study staff due to risk of behavioural disturbance. * Currently taking or having taken in the last four weeks any medication known to grossly affect the production or function of immune cells (e.g. corticosteroids, methotrexate, cyclophosphamide, mycophenolate mofetil, rituximab or other monoclonal antibody therapies). * Inability to have blood tests. Control participants: * Unacceptable risk of harm to participant or study staff due to risk of behavioural disturbance. * Currently taking or having taken in the last four weeks any medication known to grossly affect the production or function of immune cells (e.g. corticosteroids, methotrexate, cyclophosphamide, mycophenolate mofetil, rituximab or other monoclonal antibody therapies). * Inability to have blood tests. Optional lumbar puncture only: * Significant lower spinal deformity (such as spina bifida), injury (such as stenosis) or previous lower spinal surgery. * Antiplatelet or anticoagulant therapy within the 14 days prior to Lumbar Puncture procedure. * Known or suspected clotting disorder. * Clinically significant abnormality in full blood count. * Known or suspected raised intracranial pressure, assessed by study clinician. * Known or suspected allergy to local anaesthetic agent or an ingredient of the anaesthetic solution. * History of chronic or recurrent headaches, in the opinion of the investigator.