ASSOCIATION OF RAT C-REACTIVE PROTEIN AND OTHER PENTRAXINS WITH RAT LIPOPROTEINS CONTAINING APOLIPOPROTEIN-E AND APOLIPOPROTEIN-A1

C-Reactive protein (CRP) is a member of the pentraxin family of protei ns, ubiquitous components of animal serum, This study suggests that, i n serum, rat CRP is complexed with lipoprotein and may interact direct ly with apolipoprotein E. When mixed with diluted rat serum, radiolabe led 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 t hat 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 Al. 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 i ncreased the sedimentation coefficient of the major component of the a ffinity-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 di luted rat serum, human serum amyloid P (SAP) and hamster female protei n (FP), two other members of the pentraxin protein family, also had sl ightly higher sedimentation coefficients. In contrast, human CRP showe d no evidence of an interaction in rat serum or with the affinity-puri fied proteins, This selectivity coincided with the ability of these pe ntraxins to bind to O-PE with high affinity, The sedimentation propert ies of serum lipoproteins, radiolabeled with [H-3]cholesterol, also su ggested an interaction with rat CRP. Purified human apolipoprotein E i nteracted with rat CRP in a calcium-dependent manner that was inhibite d by O-PE. These results indicated that rat CRP was associated with li poproteins in serum and that the interaction may be achieved through a polipoprotein E. Association of pentraxins with lipoproteins may sugge st possible functions for pentraxins in normal situations and may be i mportant for certain pathological states, where some of the pentraxins as well as some lipoproteins have been implicated in the pathogenesis of amyloidosis.