Early in his career, Simons pursued research in the field of medical biochemistry. Both his
master's thesis and postgraduate research focused on
vitamin B12 absorption. After returning from his post-doc scholarship he continued research on vitamin B12 as well as on
blood plasma proteins, but soon started investigating
Semliki Forest virus, focusing on its
membrane and its
lipid composition and their role in the
virus budding and its transport, as the model for lipid and
protein secretion. During this period, Simons also investigated the application of
detergents in biochemistry with a special attention to their role in biological membrane research. The virus
lifecycle and how it uses components of
vesicular pathways while shuttling to the cell surface, turned Simons' attention toward vesicular transport pathways and
cell polarization. Applying
epithelial model cells –
MDCK (Madin-Darby canine kidney), he investigated lipid transport, protein sorting and their role in polarizing cells. In these studies, he described the role of the
trans-Golgi network (TGN) in protein and lipid sorting according to their destination. Simons proposed the existence of lipid microdomains in
cell membranes for the first time. is second highest cited work and Simons is fourth highest cited scientist in the field of signal transduction. Kai Simons was also recognized by
ISI Web of Knowledge, as one of the most cited scientist ever. In subsequent years, Simons continued to work on the role of lipid rafts, and more generally lipids, in cell polarization and protein sorting. He was interested also in the role of lipids and protein sorting in
neurodegenerative diseases, especially in
Alzheimer's disease. His scientific record includes more than 350
scientific articles, mostly in the field of biochemistry, molecular organization of the cell, and biochemistry and physiology of a cell membrane. Considering his work from years 1996–2007 tracked until May 2009, Simons was 12. in the list of the most frequently cited scientists in the field
cell biology with 90 articles and 16,299 citations. == Honours and awards ==