Association of rat C-reactive protein and other pentraxins with rat lipoproteins containing apolipoproteins e and A1

C-Reactive protein (CRP) is a member of the pentraxin family of proteins, ubiquitous components of animal serum. This study suggests that, in serum, rat CRP is complexee with lipoprotein and may interact directly with apolipoprotein E. When mixed with diluted rat serum, radiolabeled rat CRP showed a slightly higher sedimentation coefficient (about 15%) than that of the free protein. Elimination of calcium or addition of O-phosphorylethanolamine (O-PE), a low molecular weight compound that binds tightly to rat CRP in a calcium-dependent manner, abolished this difference. Adsorption of rat serum on a rat CRP affinity gel and elution with PE resulted in the isolation of material containing high levels of apolipoproteins E and A1. The affinity-purified preparation interacted with rat CRP and altered the sedimentation coefficient of the latter to the value observed in whole serum. Conversely, rat CRP increased the sedimentation coefficient of the major component of the affinity-purified material to that of rat CRP in rat serum (about a 1.8-fold increase). When added to the affinity-purified material or to diluted rat serum, human serum amyloid P (SAP) and hamster female protein (FP), two other members of the pentraxin protein family, also had slightly higher sedimentation coefficients. In contrast, human CRP showed no evidence of an interaction in rat serum or with the affinity-purified proteins. This selectivity coincided with the ability of these pentraxins to bind to O-PE with high affinity. The sedimentation properties of serum lipoproteins, radiolabeled with [³H]cholesterol, also suggested an interaction with rat CRP. Purified human apolipoprotein E interacted with rat CRP in a calcium-dependent manner that was inhibited by O-PE. These results indicated that rat CRP was associated with lipoproteins in serum and that the interaction may be achieved through apolipoprotein E. Association of pentraxins with lipoproteins may suggest possible functions for pentraxins in normal situations and may be important for certain pathological states, where some of the pentraxins as well as some lipoproteins have been implicated in the pathogenesis of amyloidosis.