Plasma lipoproteins are important components of the immune system

Abstract

Plasma lipoproteins (VLDL, LDL, Lp[a] and HDL) function primarily in lipid transport among tissues and organs. However, cumulative evidence suggests that lipoproteins may also prevent bacterial, viral and parasitic infections and are therefore a component of innate immunity. Lipoproteins can also detoxify lipopolysaccharide and lipoteichoic acid. Infections can induce oxidation of LDL, and oxLDL in turn plays important anti‐infective roles and protects against endotoxin‐induced tissue damage. There is also evidence that apo(a) is protective against pathogens. Taken together, the evidence suggests that it might be valuable to introduce the concept that plasma lipoproteins belong in the realm of host immune response.

Serum triglyceride and cholesterol concentrations and lipoprotein profiles in dogs with naturally occurring pancreatitis and healthy control dogs

“…[25][26][27][28][29] Typical lipoprotein changes in response to acute or chronic inflammation in humans include decreases in HDL, whereas LDL fractions and triglycerides are more variable and may show increases, decreases, or remain unchanged. [25][26][27][28][29] If the lipoproteins in the nominal LDL density range are indeed metabolically similar to TRL remnants, they could contribute to the inflammatory state. 30 In most reports, serum triglyceride concentrations tend to increase, whereas serum LDL concentrations tend to decrease, with the exception of small LDL molecules.…”

“…[25][26][27] Major changes take place in lipoprotein fractions and metabolism in response to inflammation, affecting the concentration, structure, and function of serum lipoproteins and mainly are mediated by hormones and cytokines such as tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), and IL-6. [25][26][27][28][29] Typical lipoprotein changes in response to acute or chronic inflammation in humans include decreases in HDL, whereas LDL fractions and triglycerides are more variable and may show increases, decreases, or remain unchanged. [25][26][27][28][29] If the lipoproteins in the nominal LDL density range are indeed metabolically similar to TRL remnants, they could contribute to the inflammatory state.…”

“…30 In most reports, serum triglyceride concentrations tend to increase, whereas serum LDL concentrations tend to decrease, with the exception of small LDL molecules. [25][26][27][28][29] These changes in lipids and lipoproteins that occur during inflammation are part of the innate immune response and are believed to benefit the host through various mechanisms such as redistribution of nutrients to immune cells and binding of endotoxins and other biological substances. 29,31 Similar changes were observed in our study with respect to HDL and triglycerides.…”

Apolipoprotein(a) inhibits lipopolysaccharide-induced IL-6 secretion in human astrocytoma cell line by interfering with lipopolysaccharide signaling

“…Although the physiological roles of Lp(a) remain elusive, there is some evidence that apo(a) is an active component of the immune system [23], with a still open question as to whether it protects against pathogens [10,14] and/or has pro-inflammatory properties [11]. Our data indicate that r-apo(a) does not have agonistic activity in IL-6 production by U373 cells; conversely, we demonstrate that it is able to inhibit LPS-induced IL-6 secretion, in a dose-dependent manner.…”

Functional primate genomics—leveraging the medical potential

“…Genes annotated in the immune system show evidence for positive selection more often than most other categories [11], and pathogenic environment had a larger impact on genetic differences among human populations than diet regimes or climatic conditions [44]. Since evidence is accumulating that lipoproteins in general are important components of the immune system [45] and apo(a) regulates neutrophil recruitment [46], a physiological function of Lp(a) in this context is certainly well compatible with the evolution of Lp(a). Alternative explanations, such as a role of Lp(a) in wound healing [47], would need to explain why Lp(a) evolved independently in old world monkeys and hedgehogs and is absent in other mammals and primates.…”