ELISA is a blood test that detects antibodies to HIV, with a positive result indicating exposure to the virus, though there may be false positives requiring a Western blot test for verification. Hodgkin's disease is a cancer of the lymphatic cells found in lymph nodes, named after its discoverer Thomas Hodgkin. Sarcoidosis is a disease of unknown causes that forms fibrous lesions commonly appearing in multiple organs including lymph nodes, liver, and lungs.