IMMUNOHISTOCHEMICAL DEMONSTRATION OF ENZYMATICALLY MODIFIED HUMAN LDLAND ITS COLOCALIZATION WITH THE TERMINAL COMPLEMENT COMPLEX IN THE EARLY ATHEROSCLEROTIC LESION

Treatment of low density lipoprotein (LDL) with degrading enzymes tran sforms the molecule to a moiety that is micromorphologically indisting uishable from lipoproteinaceous particles that are present in atherosc lerotic plaques, and enzymatically modified LDL (E-LDL), but not oxidi zed LDL (ox-LDL), spontaneously activates the alternative complement p athway, as do lesion lipoprotein derivatives. Furthermore, because E-L DL is a potent inducer of macrophage foam cell formation, we propose t hat enzymatic degradation may be the key process that renders LDL athe rogenic. in this article, we report the production of two murine monoc lonal antibodies recognizing cryptic epitopes in human apolipoprotein B that become exposed after enzymatic attack on LDL, One antibody reac ted with LDL after single treatment with trypsin, whereas recognition by the second antibody required combined treatment of LDL with trypsin and cholesterol esterase. In ELISAs, both antibodies reacted with E-L DL produced in vitro and with lesion complement activator derived from human atherosclerotic plaques, but they were unreactive with native L DL or ox-LDL. The antibodies stained E-LDL, but not native LDL or ox-L DL, that had been artificially injected into arterial vessel walls. Wi th the use of these antibodies, we have demonstrated that early human atherosclerotic coronary lesions obtained at autopsy as well as lesion s examined in freshly explanted hearts always contain extensive extrac ellular deposits of E-LDL. Terminal complement complexes, detected wit h a monoclonal antibody specific for a C5b-9 neoepitope, colocalized w ith E-LDL within the intima, which is compatible with the proposal tha t subendothelially deposited LDL is enzymatically transformed to a com plement activator at the earliest stages in lesion development.