Complex sentence: After being diagnosed with sarcoidosis, he developed a hypothesis for how autoimmune diseases develop and persist, and proposed a biomedical treatment for chronic inflammatory diseases; the treatment became known as the Marshall Protocol (MP).
Split into simpler sentences: After being diagnosed with sarcoidosis, he began to develop a hypothesis for how autoimmune diseases develop and persist. This understanding of disease is used as the basis for a biomedical treatment for chronic inflammatory diseases, which became known as the Marshall Protocol (MP).