We carry out in situ single-molecule measurements of the specific interaction between apolipoprotein A-I (apoA-I) and ATP binding cassette transporter A1 (ABCA1) on THP-1 cells. Single-molecule force spectroscopy shows that similar to normal apoA-I, the dysfunctional apoA-I from diabetes patients interacts with ABCA1 via two different binding sites on the cells. The strength of dysfunctional apoA-I binding to a high-capacity binding site is 26.5 (-)4.9 pN. The minor direct apoA-I/ABCA1 binding strength is 56.7 (-)4.1 pN. These results facilitate a pathological understanding of the mechanisms that underlie the specific interaction of apoA-I and ABCA1 at the single-molecule level.