Apolipoprotein C-I is a protein component of lipoproteins that in humans is encoded by the APOC1 gene. The protein encoded by this gene is a member of the apolipoprotein C family. This gene is expressed primarily in the liver, and it is activated when monocytes differentiate into macrophages. Alternatively spliced transcript variants have been found for this gene, but the biological validity of some variants has not been determined.