Comparison of two commercial nephelometric methods for apoprotein A-I and apoprotein B with standardized apoprotein A-I and B radioimmunoassays

Normotriglyceridemic and hypertriglyceridemic samples were analyzed for apoproteins A-I and B using the Beckman Array System and the Behring Nephelometer, and the nephelometric values were compared to values obtained by highly standardized radioimmunoassays developed at the Northwest Lipid Research Center. Although the means of the apoA-I values obtained by each method were similar, comparison of sample values by least-squares regression analysis revealed large differences (Sy = 20 mg/dl for Beckman, Sy = 18 mg/dl for Behring) (Sy = standard error of the estimate) regardless of whether the comparison included hypertriglyceridemic samples. For normotriglyceridemic samples, there was good agreement between apoB values obtained by the Behring Nephelometer and those obtained by RIA (r = 0.91, m = 1.03, Sy = 12 mg/dl). However, significantly higher apoB values were obtained on hypertriglyceridemic samples by the Behring Nephelometer. ApoB values for normotriglyceridemic samples obtained by the Beckman System and RIA showed fairly good correlation (r = 0.86, m = 0.71, Sy = 14 mg/dl). However, the nephelometric values for normotriglyceridemic samples averaged 29% lower than those obtained by RIA. This difference could largely be accounted for by the low apoprotein B value assigned to the Beckman calibrator. Significantly lower apoprotein B values were obtained on hypertriglyceridemic samples by the Beckman Nephelometer even after correction for calibration differences. Apoprotein values obtained by nephelometric methods may be inaccurate, particularly if the samples are hypertriglyceridemic.     

Displacement of the human apoprotein A-I by the human apoprotein A-II from complexes of (apoprotein A-I)-phosphatidylcholine-cholesterol

Reassembly experiments, involving isolated human apoproteins A-I and A-II and (dimyristoylglycerophosphocholine)-cholesterol vesicles were performed with apoprotein mixtures at apoprotein A-I/A-II molar ratios varying between 0 and 3. The apoproteins were incubated at 24 degrees C. 28 degrees C and 32 degrees C with either pure dimyristoyl-glycerophosphocholine vesicles or with dimyristoylglycerophosphocholine cholesterol vesicles containing 2, 5, 10, 15 mol/100 mol cholesterol. The kinetics of association were followed by measuring the increase of the fluorescence polarization ratio after labeling the lipids with diphenyl hexatriene. The complexes were separated from the free protein by gradient ultracentrifugation. Total protein was assayed and the apoproteins A-I and A-II were quantified separately by immunonephelometry. The content of apoprotein A-I was also monitored by measuring the intrinsic tryptophan fluorescence. The results suggest that apoprotein A-II has a greater affinity than apoprotein A-I for the phospholipid-cholesterol vesicles and that apoprotein A-II is able to quantitatively displace apoprotein A-I from the lipid-protein complexes. The content of apoprotein A-II in the complexes increases proportionally to the concentration of apoprotein A-II in the incubation mixture until saturation is reached. At saturation the dimyristoylglycerophosphocholine/apoprotein A-II ratio in the complex is dependent upon the cholesterol content of the original vesicles and increases from 60 to 275 mol/mol between 0 and 15 mol/100 mol cholesterol. From these experiments one can calculate that 1 mol human apoprotein A-I is displaced by 2 mol human apoprotein A-II.     

Lipids and apolipoproteins A-I, B and C-II and different rapid weight loss programs (weight lifters, wrestlers, boxers and judokas)

Apolipoproteins A-I, B, C-II and lipids were studied before and after rapid weight loss schedules. The compared groups were all athletic. Apolipoproteins were determined by electroimmunoassay methods using apoproteins purified by chromatofocusing column method. Dextran T10 was shown to increase rocket height in ApoB assay. Over 1% Dextran concentrations gave poor response. The linearity during calibration was from 0.3 to 3.0 g ApoB/l. Baseline values of ApoA-I in wrestlers, weightlifters, boxers and judokas were slightly higher as compared to "normal" population; ApoB was clearly reduced (mean value of 690 mg/l). Weight-loss was significant in each experimental group; mean value of 4.1% in active exercise, sauna and diuretic groups together. Compared as the whole sportsmen group in passive weight loss (or sauna) and diuretic groups the most pronounced changes were seen to be elevated apoprotein concentrations, whereas weight-loss by active rapid exercise resulted no apoprotein changes, but instead an increment in HDL cholesterol and decrement in triglycerides, respectively. The present study was the first to evaluate baseline values of apoproteins A-I, B and C-II in first class athletes and also the possible changes in these and lipid values in rapid weight-loss practices.     

A comparison of two methods to investigate the metabolism of human apolipoproteins A-I and and A-II.

Two methods are compared for measuring the kinetic parameters of apolipoprotein A-I and A-II metabolism in human plasma. In the first, high density lipoprotein apoproteins were radioiodinated in situ in the lipoprotein particle (endogenous apoprotein labeling) while in the second, individually labeled apolipoprotein A-I or A-II was incorporated into the particle by in vitro incubation (exogenous apoprotein labeling). The catabolic clearance rate of exogenously labeled apolipoprotein A-I was consistently faster than that of endogenous apolipoprotein A-I. Conversely, endogenously and exogenously labeled apolipoprotein A-II were catabolized at identical rates. The fractional plasma clearance rates of endogenous apolipoproteins A-I and A-II were the same.     

An alternate apoprotein conformation in high density apolipoprotein discoidal complexes. A Fourier transform infra-red study.

Discoidal complexes have been prepared from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and the apoproteins of HDL3 (apo HDL3) or purified apo A-I. Gel electrophoresis established that apo HDL3 contained 74% apo A-I. Deconvolution and curve-fitting of the infra-red amide I band of the apoprotein in the lipid-protein complex revealed a secondary structure containing approximately 40% alpha-helix and 50% beta-structure. This contrasted with the results from circular dichroism studies (Surewicz et al. (1986) J. Biol. Chem., 261, 16191) of apo A-I/DMPC complexes which predicted 68% alpha-helix and 7% beta-structure. The discrepancy between the two methods and limitations of the two techniques for lipoproteins is discussed.     

Origin and transport of the A-I and arginine-rich apolipoproteins in mesenteric lymph of rats.

Transport of apolipoprotein A-I and argininerich apolipoprotein in mesenteric lymph was examined in rats given constant intraduodenal infusions of saline, glucose in saline, or emulsified fat. Lymph flow in all groups was constant from 5 to 50 hr after beginning the infusions. Lymphatic transport of triglycerides was about 20-fold greater and transport of apoprotein A-I was about twofold greater in fat-infused rats than in the other two groups. In each group transport of apoprotein A-I bore a significant positive relationship to transport of triglycerides. Lymphatic transport of the arginine-rich apoprotein was only 6-12% of that of apoprotein A-I and was more closely related to lymphatic transport of total protein than to that of triglycerides. In fat-infused rats given [(3)H]lysine intraduodenally, about two-thirds of the (3)H in the chylomicron proteins was in apoprotein A-I and only about 1% was in the arginine-rich apoprotein. Estimated specific activity of chylomicron proteins was highest for apoprotein A-I and apoprotein A-IV, and lowest for the arginine-rich apoprotein and proteins of low molecular weight (mainly C apoproteins). In fat-infused rats given constant intravenous infusions of radioiodinated high density lipoproteins from blood plasma, the specific activity of apoprotein A-I in lymph chylomicrons was only about 5% of that of apoprotein A-I in blood high density lipoproteins, indicating that more than 90% of the apoprotein A-I in chylomicrons was synthesized in the intestine. From these and other data it is concluded that both the intestine and liver are significant sources of apoprotein A-I whereas only the liver synthesizes significant amounts of the arginine-rich apoprotein.     

Changes in the concentration of plasma lipoproteins and apoproteins following the administration of Triton WR 1339 to rats.

Changes in whole plasma and lipoprotien apoprotein concentrations were determined after a single injection of Triton WR 1339 into rats. Concentrations of apoproteins A-I (an activator of lecithin:cholesterol acyl transferase), arginine-rich apoprotein (ARP), and B apoprotein were measured by electroimmunoassay. The content of C-II apoprotein (an activaor of lipoprotein lipase) was estimated by the ability of plasma and lipoprotein fractions to promote hydrolysis of triglyceride in the presence of cow's milk lipase and also by isoelectric focusing on polyacrylamide gels. Apoproteins C-II and A-I were rapidly removed from high density lipoprotein (HDL) after Triton treatment and were recovered in the d 1.21 g/ml infranate fraction. A-I was then totally cleared from the plasma within 10--20 hr after injection. Arginine-rich apoprotein was removed from HDL and also partially cleared from the plasma. The rise in very low density lipoprotein (vldl) apoprotein that followed the removal of apoproteins from HDL was mostly antributed to the B apoprotein, although corresponding smaller increases were observed in VLDL ARP and C apoproteins. The triglyceride:cholesterol, triglyceride:protein, and B:C apoprotein ratios of VLDL more closely resembled nascent rather than plasma VLDL 10 hr after Triton injection. These studies suggest that the detergent may achieve its hyperlipidemic effct by disrupting HDL and thus removing the A-I and C-II proteins from a normal activating environment compirsing VLDL, HDL, and the enzymes. The possible involvement of intact HDL in VLDL catabolism is discussed in relation to other recent reports which also suggest that abnormalities of the VLDL-LDL system may be due to the absence of normal HDL.     

The role of the structural organization of apoprotein E in cholesterol binding

The ability of some proteins to bind cholesterol was accompanied by a decrease of turbidity of aqueous cholesterol suspensions and correlated with a quantity of arginine residues in them. Maximum clearing of aqueous cholesterol suspensions at the addition of proteins containing equimolar arginine concentrations was observed in the presence of apoproteins E and A-I. Optical rotatory dispersion spectra of apoprotein E, polyarginine and histone H3 have shown the influence of sterol on the secondary structure of apoprotein E only.     

Proteolysis of apoprotein B during the transfer of very low density lipoprotein from hens' blood to egg yolk

We report an example of the enzymic cleavage of an apoprotein B (apoB), the main apoprotein in the very low density lipoprotein (VLDL) of laying hens' blood, in a normal biological process, the formation of egg yolk. Plasma VLDL was labeled in vivo with 3H-amino acids, isolated by centrifuging, and injected into another laying hen. Yolk VLDL was isolated and its apoproteins were separated. ApoB was not detected in this lipoprotein. Most of the label originally in apoB was distributed among four smaller yolk apoproteins, apovitellenins III to VI, which are a large proportion of the apoproteins of VLDL in yolk. This distribution of 3H suggested that 80% of apoB was cleaved at three places. One yolk apoprotein, apovitellenin II, was not labeled, indicating that it did not originate from an apoprotein in plasma VLDL. The site for cleavage of apoB in the ovarian tissue has not been determined, but cleavage may occur during receptor-mediated endocytosis. The pattern of cleavage of apoB during transfer to yolk was not imitated by some known proteolytic enzymes.     

Interaction between hepatic microsomal membrane lipids and apolipoprotein A-I

Incubation of apoprotein A-I (apo-A-I), the major protein component of human high density lipoprotein, with rat liver microsomal membranes under conditions of elevated pH and ionic strength leads to the production of a soluble protein:lipid complex (A-I/MM complex). The A-I/MM complex, as purified by density gradient centrifugation and agarose column chromatography, possesses a lipid composition similar to the hepatic microsomal membrane and a protein/lipid ratio similar to that of plasma high density lipoproteins, but markedly different from that of recombinant particles prepared with synthetic lipids. The A-I/MM complex constitutes a more physiological recombinant particle than can be formed using synthetic lipids and may be a suitable model for the newly assembled intracellular high density lipoproteins. Incubation of the erythrocyte plasma membranes with apo-A-I under the same conditions as used with microsomal membranes fails to generate any lipid:apoprotein complexes. This membrane specificity for forming soluble lipoprotein complexes suggests that the microsomal membranes possess a unique feature, possibly their lipid composition, which render them particularly suitable to serve as lipid donors to the apoproteins which are undergoing assembly within the endoplasmic reticulum/Golgi organelles.     

The apoprotein B-independent hepatic uptake of chylomicron remnants.

Rat lymph chylomicrons were treated with Pronase resulting in particles completely devoid of surface apoproteins. On re-incubation with serum, the Pronase-treated chylomicrons re-acquired, by transfer from other lipoproteins, all apoproteins except apoprotein B, which is water-insoluble and non-transferable. When two groups of rats were injected with [3H]cholesterol-labelled control or Pronase-treated chylomicrons, radioactivity was incorporated into the liver of both groups at similar rates. It is concluded that the remnants of the control and Pronase-treated chylomicrons formed in the vascular space were recognized and taken up by liver cells by a process that does not require apoprotein B.     

Distribution of apolipoproteins A-I and B among intestinal lipoproteins

Chylomicrons and very low density lipoproteins (VLDL) are produced by the intestine and these nascent particles are thought to be similar to their counterparts in intestinal lymph. To study the relationship between these lipoproteins within the cell and those secreted into the lamina propria and lymph, we have isolated enterocytes, lamina propria, and mesenteric lymph from rats while fasted and after corn oil feeding. Apolipoprotein A-I and B content were measured by radioimmunoassay in cell, lamina propria, and lymph fractions separated by Sepharose 6B and 10% agarose chromatography, and by KBr isopycnic density centrifugation. ApoA-I in the cell and the underlying lamina propria was found partly in those fractions in which chylomicron and very low density lipoproteins (chylo-VLDL) and high density lipoproteins (HDL) elute, but more abundantly where unassociated 125I-labeled apoA-I was eluted. In the lymph, however, 74% of apoA-I eluted in the HDL region and no peak of free apoA-I was found. ApoB and apoC-III within the enterocyte were found distributed in the position of particles eluting not only with chylomicrons and VLDL, but also in the regions corresponding to LDL and HDL. In the lamina propria and lymph, on the other hand, most of the apoB was found in the region of VLDL and chylomicrons. These results indicate that the patterns in lymph lipoproteins and the lamina propria do not exactly mirror the distribution of apoA-I and B among lipoproteins inside the cell. This may be because intracellular apoproteins may be unassociated with lipoproteins, or they could be associated with lipoproteins in various stages of assembly of protein with lipids. Furthermore, the apoprotein composition of intestinal lipoproteins is altered after secretion from the enterocyte. Finally, not all apoproteins seem to be secreted in association with identifiable lipoprotein particles from the enterocyte.     

Protective effect of lipoproteins containing apoprotein A-I on Cu2+-catalyzed oxidation of human low density lipoprotein

Two apoprotein A-I (apoA-I)-containing lipoproteins, one containing apoA-I and apoA-II (LpA-I/A-II) and the other containing only apoA-I (LpA-I), were examined for their effect on Cu2+-mediated oxidation of low density lipoprotein (LDL). The presence of LpA-I or LpA-I/A-II prevented LDL oxidation when assessed by the electrophoretic mobility, apoprotein B fragmentation and amounts of thiobarbituric acid-reactive substances. The protection of LDL oxidation by these lipoproteins was effective for up to 6 h, with LpA-I being more active than LpA-I/A-II. Results from these in vitro model experiments raise a possibility that LpA-I may play a role in protecting LDL from Cu2+-mediated oxidation.     

Plasma levels of lipids and apoprotein in a group of middle-school students 11-14 years of age: preliminary data]

Plasma lipids and apoprotein A and B levels were measured in 63 children, of both sexes, in the age range 11-14 years. The children have been subjected to a blood drawing after a 12 hour fast at least. Statistical analysis proves that total cholesterol (TC) is positively correlated with triglycerides (TG), HDL cholesterol (HDL) with apolipoproteins A (Apo A), apolipoproteins A (Apo A) with apoproteins B (Apo B). In the end we confirm the utility of determining plasma lipids and apoproteins to estimate lipidic risk for atherosclerosis in pediatric age.     

Radioimmunoassay of apolipoprotein A-I of rat serum.

A double antibody radioimmunoassay technique was developed for quantification of apolipoprotein A-I, the major apoprotein of rat high density lipoprotein. Apo A-I was labeled with 125I by the chloramine-T method. 125I-labeled apo A-I had the same electrophoretic mobility as unlabeled apo A-I and more than 80% of the 125I was precipitated by rabbit anti apo A-I antibodies. The assay is sensitive at the level of 0.5-5 ng, and has intraassay and interassay coefficients of variation of 4.5 and 6.5% respectively. The specificity of the assay was established by competitive displacement of 125I-labeled apo A-I from its antibody by apo A-I and lipoproteins containing apo A-I, but not by rat albumin and other apoproteins. Immunoreactivity of high density lipoprotein and serum was only about 35% of that of their delipidated forms when Veronal buffer was used as a diluent. Inclusion of 5 mM sodium decyl sulfate in the incubation mixture brought out reactivity equivalent to that found after delipidation. Completeness of the reaction was verified by comparison with the amount of apo A-I in chromatographic fractions of the total apoprotein of high density lipoprotein. Content (weight %, mean values +/- S.D.) of immunoassayable apo A-I was: 62.3 +/- 5.9 in high density lipoprotein; 1.7 +/- 0.3 in low density lipoprotein; 0.09 +/- 0.03 in very low density lipoprotein and 25.0 +/- 5.0 in lymp chylomicrons. Concentration in whole serum was 51.4 +/- 8.9 mg/dl and 33.6 +/- 4.1 mg/dl for female and male rats, respectively (p less than 0.002), equivalent to the sex difference in concentration of high density lipoprotein. 95% of the apo A-I in serum was in high density lipoprotein, 5% in proteins of d greater than 1.21 g/ml and less than 1% in lipoproteins of d less than 1.063 g/ml.     

The surface properties of apolipoproteins A-I and A-II at the lipid/water interface

The monolayer system was employed to investigate the relative affinities of apolipoproteins A-I and A-II for the lipid/water interface. The adsorption of reductively 14C-methylated apolipoproteins to phospholipid monolayers spread at the air/water interface was determined by monitoring the surface pressure of the mixed monolayer and the surface concentration of the apoprotein. ApoA-II has a higher affinity than apoA-I for lipid monolayers; for a given initial surface pressure, apoA-II adsorbs more than apoA-I to monolayers of egg phosphatidylcholine (PC), distearoyl-PC and human high-density lipoprotein (HDL3) surface lipids. Comparison of the molecular packing of apolipoproteins A-I and A-II suggests that apoA-II adopts a more condensed conformation at the lipid/water interface compared to apoA-I. The ability of apoA-II to displace apoA-I from egg PC and HDL3 surface lipid monolayers was studied by following the adsorption and desorption of the reductively 14C-methylated apolipoproteins. At saturating subphase concentrations of the apoproteins (3.10(-5) g/100 ml), two molecules of apoA-II absorbed for each molecule of apoA-I displaced. This displacement was accompanied by an increase in surface pressure. An identical stoichiometry for the displacement of apoA-I from HDL particles by apoA-II has been reported by others. At low subphase concentrations of apoproteins (5.10(-6) g/100 ml), the apoA-I/lipid monolayer was not fully compressed and could accommodate the adsorbing apoA-II molecules without displacement of apoA-I molecules. ApoA-I molecules were unable to displace apoA-II from the lipid/water interface. The average residue hydrophobicity of apoA-II is higher than that of apoA-I; this may contribute to the higher affinity of apoA-II for lipids compared to apoA-I. The probable helical regions in apolipoproteins A-I and A-II were located using a secondary structure prediction algorithm. The analysis suggests that the amphiphilic properties of the alpha-helical regions of apoA-I and apoA-II are probably not significantly different. Further understanding of the differences in surface activity of these apolipoproteins will require more knowledge of their secondary and tertiary structures.     

Incorporation of cholesterol into serum high density lipoprotein apoprotein and recombinants

The uptake of cholesterol (CHL) by serum high density lipoprotein (HDL) delipidated apoproteins and phospholipid-apoprotein recombinants has been studied with two methods; by incubation with Celite-dispersed cholesterol or with cholesterol crystals. The apoproteins bind very small amounts of cholesterol with a maximum of about 6 micrograms/mg apoprotein. Recombinants with dimyristoyl phosphatidylcholine (DMPC) or egg phosphatidylcholine (EPC) as phospholipid component gave similar values for cholesterol uptake. The initial rate for uptake from Celite-cholesterol by recombinants was high (0.1 mol cholesterol/mol phospholipid/h) and somewhat higher than that for phospholipid vesicles. The maximal uptake was by gel filtration shown to depend on the size of the complexes with values about 0.95 mol cholesterol per phospholipid for vesicular complexes, 0.75 for discoidal complexes and between 0.5 and 0.2 for small 'protein-rich' complexes. During the incubation of recombinants with cholesterol there was considerable decomposition of discoidal complexes and formation of larger ones. The results show that phospholipid-apoprotein complexes are efficient acceptors for cholesterol but also that about 25% of the phospholipid in the discoidal complexes is excluded from interaction with cholesterol by interaction with apoprotein.     

Estimation of lipoprotein and apoprotein distribution in rat plasma by cumulative density ultracentrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Lipoprotein distribution in rat plasma determined after sequential ultracentrifugation (requiring 8 days of centrifugation to separate lipoproteins in five density classes), was compared to estimates based upon cumulative density ultracentrifugation (46 hr of ultracentrifugation). In general comparable values were obtained by the two methods with regard to protein, total cholesterol, cholesteryl ester, free cholesterol, and triacylglycerol distribution. However, the HDL3 protein concentration found by sequential ultracentrifugation was only about 50% of that found after the cumulative procedure. Apolipoproteins in lipoproteins isolated by the two methods were well separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Color of the stained bands was extracted and read photometrically. A linear standard curve was obtained with albumin. Absorbance corresponding to 1 microgram/ml was 0.057. Below d = 1.100 g/ml (HDL2b) the two ultracentrifugation methods gave comparable results for all apoproteins. In contrast to this the level of apo A-I, apo E, and apo A-IV in the more dense types of HDL was higher when estimated by cumulative than by sequential ultracentrifugation. In HDL3 isolated by sequential ultracentrifugation the apo A-IV, apo E, and apo A-I concentrations were 51, 31, and 45% respectively, of values found after cumulative ultracentrifugation. The results indicate that cumulative density ultracentrifugation, followed by colorimetric determination of apoproteins separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is a useful approach when studying lipoprotein distribution in rat plasma.     

Molecular weights of apoprotein B obtained from human low-density lipoprotein (apoprotein B-PI) and from rat very low density lipoprotein (apoprotein B-PIII)

Human low-density lipoproteins (LDL) were isolated from single donors by differential centrifugation between densities of 1.020 and 1.050 g/mL. The LDL were reduced and alkylated in 7 M guanidine hydrochloride, and the lipid was removed by multiple extractions in the cold with a mixture of diethyl ether and ethanol. Sedimentation studies on the resultant human apoprotein B (apoprotein B-PI) at low concentrations in 6.00 M guanidine hydrochloride showed a single sharp boundary with a sedimentation coefficient of 2.15 +/- 0.04 S at 25 degrees C, uncorrected for viscosity or density. Diffusion experiments performed in the same solvent at low speeds in the analytical ultracentrifuge gave a D25 = 0.694 +/- 0.043 Fick. Combining these values with an apparent specific volume of 0.703 mL/g yielded a molecular weight of 387 000, indistinguishable from that obtained by sedimentation equilibrium analysis in 7 M guanidine hydrochloride. Similar values were also obtained by calibrated sedimentation analysis, by Sepharose 2B chromatography in guanidine hydrochloride, and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Rat very low density lipoproteins (VLDL), isolated from sera of Triton WR1339 treated animals, were used as the source of rat apoprotein B-PIII. The delipidated VLDL were solubilized in sodium dodecyl sulfate, and apoprotein B-PIII was isolated by Sepharose 4B chromatography. With appropriate corrections for density and viscosity, the behavior of rat apoprotein B-PIII was identical, upon analytical ultracentrifugation, in 6 and 7.7 M guanidine hydrochloride, corresponding to sedimentation and diffusion coefficients of 1.47 S and 0.92 Fick, respectively, in 6 M guanidine hydrochloride. These data may be combined to yield a molecular weight of 210 000. Similar values were obtained by calibrated sedimentation analysis, by Sepharose 2B chromatography in guanidine hydrochloride, and by polyacrylamide gel electrophoresis in sodium dodecyl sulfate.     

Comparison of three ELISA kits for the differentiation of foot-and-mouth disease virus-infected from vaccinated animals

A study was performed to validate 3 FMDV 3ABC-I-ELISA kits developed in China for the differentiation of FMDV infected and vaccinated animals. Sets of sera from naive and vaccinated cattle as well as from cattle that had been infected were tested for antibodies against nonstructural proteins (NSPs) of FMDV by commercial diagnosis kits, Ceditest® FMDV-NS (Ceditest® kit), UBI® FMDV NONSTRUCTURAL PROTEIN ELISA DIRECTION INSERT (UBI® kit) and a FMDV 3ABC-I-ELISA kit developed at the Lanzhou Veterinary Research Institute. The test parameters (sensitivity and specificity) of the three kits were determined, and the result obtained from FMD 3ABC-I-ELISA kit was compared with that obtained from two foreign kits. The results indicated that the coincidence rate between the FMDV 3ABC-I-ELISA and Ceditest® kits was 98.05%, and the coincidence rate between the FMDV 3ABC-I-ELISA and UBI® kits was 94.4%; the sensitivity of both Ceditest® and FMDV 3ABC-I-ELISA kit was 100%. However, the sensitivity of the UBI® kit was only 81.8%. With sera from naive or vaccinated non-infected animals, the specificity of all tests exceeded 90%.