High cholesterol may protect against infections and atherosclerosis

Extract

Introduction

Many researchers have suggested that the blood lipids play a key role in the immune defence system.^1–21 There is also a growing understanding that an inflammatory response of the arterial intima to injury is a crucial step in the genesis of atherosclerosis. and that infections may be one type of such injury.²² These two concepts are difficult to harmonize with the low-density-lipoprotein (LDL) receptor hypothesis, according to which high LDL cholesterol is the most important cause of atherosclerosis. However, the many observations that conflict with the LDL receptor hypothesis, may be explained by the idea that high serum cholesterol and/or high LDL is protective against infection and atherosclerosis.

Laboratory evidence

Lipopolysaccharide, or endotoxin, the main pathogenic factor of Gram-negative bacteria, binds rapidly to lipoproteins,⁶ mainly LDL,⁷ and lipoprotein-bound endotoxin is unable to activate the secretion of various cytokines by monocytes in vitro.^6,7,10 Also, Staphylococcus aureus α-toxin, a toxin produced by most pathogenic Staphylococcus strains and causing damage to a wide variety of cells, is bound and almost totally inactivated by human serum and purified LDL, as estimated by haemolytic titration.³