Rabbit Albumin Research Articles

Effects of a selective thromboxane A2 synthetase inhibitor on immune complex glomerulonephritis.

It has been reported that agents which block the prostaglandin system inhibit the development of glomerulonephritis. However, the mechanisms of these effects are not clear. We studied the effect of a selective thromboxane A2 (TxA2) synthetase inhibitor, 1-benzylimidazole (BIm), on the immune complex glomerulonephritis produced by bovine serum albumin (BSA) in New Zealand white rabbits. As the BSA nephritis developed, there was no change of creatinine (Cr), serum urea nitrogen (SUN), or creatinine clearance (Ccr), but urinary protein excretion increased almost 3-fold. Coagulation and fibrinolytic studies suggested a hypercoagulable state and increased fibrinolytic activity. Platelet aggregation showed the reduction of maximum aggregation induced by ADP and collagen. Histological examination by light microscopy, immunofluorescence, and electron microscopy revealed glomerular polymorphonuclear leukocyte (PMN) infiltration, mononuclear cell (MON) proliferation, and fibrin deposition. In 70% of the rabbits, IgG and C3 deposits were seen by immunofluorescence mainly in mesangial areas. The administration of BIm to BSA nephritis had no effects on Cr, SUN or Ccr, but it significantly lessened the proteinuria. The study of coagulation and fibrinolytic activity suggested a less hypercoagulable state, and more efficient fibrinolysis occurred than in the group without BIm. BIm tended to normalize platelet aggregation. It also lessened the histological PMN infiltration (p less than 0.05), MON proliferation (p less than 0.01), and fibrin deposition (p less than 0.05). These data suggest that TxA2 may play an important pathogenetic role in the development and progression of glomerulonephritis.

The effect of components of rabbit pulmonary surfactant on the activity of phospholipases.

This study investigates the ability of two components of pulmonary surfactant, protein and phosphatidylglycerol, to inhibit the action of phospholipases against phosphatidylcholine. Broncho-alveolar protein, prepared by de-lipidation of rabbit lung lavage material had an inhibitory effect on phospholipases A1 and A2 from rabbit lung lysosomes, comparable to the effect of bovine serum albumin. The degree of inhibition was found to increase with increasing enzyme activity. De-lipidated broncho-alveolar protein was separated into two fractions by gel chromatography. Inhibitory activity was associated only with the second peak, corresponding to rabbit albumin. The effect of phosphatidylglycerol (PG) on the activity of phospholipases A against dipalmitoyl phosphatidylcholine and unsaturated phosphatidylcholine (USPC) was investigated, and compared with the effects of two substrate analogues on the hydrolysis of USPC. There was no indication of true inhibition by PG, but some stimulation of USPC hydrolysis by 10 mol % PG. The relevance of these findings to the fate of surfactant in vivo is discussed.

Characterization of rabbit surfactant-associated proteins

In the present study, the apolipoproteins associated with a purified surfactant fraction isolated from lung lavage of adult rabbits were characterized. Surfactant purity was assessed by the glycerophospholipid composition and by electron microscopic examination. The purified surfactant was delipidated and the apolipoproteins were analyzed by two-dimensional polyacrylamide gel electrophoresis. By use of this technique at least eight proteins or families of proteins were found to be associated with surfactant. Four of these apolipoproteins were families of proteins of 55–70, 29–36, 26–28 and 22–23 kilodaltons (kDa). All of these apolipoprotein families had acidic isoelectric points (p I < 5.6), and were specifically bound to a Con A-Sepharose matrix, indicative that these apolipoprotein families are modified by oligosaccharide side-chains. The finding that neuraminidase treatment degraded the 29–36 kDa family is suggestive that this apolipoprotein family contains sialic acid residues. Three major proteins of 66, 43–45 and 35 kDa and a minor protein of 86 kDa were also observed. These proteins had isoelectric points in the more neutral range (p I 6.0–6.5). The 66 kDa protein (p I 6.4) had the same apparent molecular weight and isoelectric point as the major protein of delipidated rabbit serum and as purified rabbit albumin, which suggests that this protein is albumin. These findings are indicative that the apolipoproteins of surfactant are more numerous and complex than previously reported.

DISTRIBUTION OF TRANSFERRIN AND TRANSFERRIN RECEPTORS IN THE RABBIT PLACENTA

The quantity and distribution of transferrin and transferrin-binding sites in the placenta were investigated in rabbits on the 28th-29th days of pregnancy. The animals were injected intravenously with a mixture of 59Fe-125I-labelled rabbit diferric transferrin and 131I-labelled rabbit albumin. The binding of transferrin to placentas removed 3-75 min later was determined by using the 131I-labelled albumin values to correct for tissue content of plasma. Mean values for transferrin binding of 1460 and 560 micrograms/g tissue were obtained 3-15 and 45-75 min after injection, respectively. Gel filtration of placental extracts prepared with the non-ionic detergent, Teric 12A9, showed that the 125I-labelled transferrin bound to a large molecular weight component which had the properties of a specific receptor. The receptor had a higher affinity for diferric transferrin than for apotransferrin. The subcellular distribution of transferrin binding sites was determined by differential centrifugation of placental homogenates and by electron microscope autoradiography. The results with the former method indicated that the transferrin was bound to the microsomal fraction of the cells. Autoradiography showed that the majority of the transferrin molecules were at intracellular sites, mainly on the membrane of intracellular vesicles. It is concluded that iron-containing transferrin molecules enter the trophoblast cells by endocytosis or via a canalicular system after binding to cell membrane receptors. The higher affinity of the receptors for diferric transferrin than for apotransferrin explains the difference in amount of transferrin binding found within 15 min of injecting labelled diferric transferrin and that found 45-75 min later when much of the iron had been removed from the transferrin.

Principles, problems, and strategies in the use of antigenic mixtures for the enzyme-linked immunosorbent assay.

Competition between proteins and other macromolecules for adsorption sites on plastic was studied with the enzyme-linked immunosorbent assay (ELISA) to determine effects of the use of antigenic mixtures or extracts of organisms on assays of antibodies and antigens by ELISA. A comparison of a number of different polystyrene microplates with bovine albumin and human immunoglobulin G (IgG) as antigens showed two major classes of plates; those which adsorbed albumin poorly and those which adsorbed albumin well. IgG adsorbed well on all plates, but plates which adsorbed albumin best also gave significant background levels of nonspecific binding of conjugate. When mixtures of IgG and bovine serum albumin were used as coating antigens, significant competition was observed; the component present at 1% or less in the mixture was essentially undetectable unless excessive amounts of conjugate were used. The important factor was the ratio of competitor to antigen, not the absolute amount. Other proteins (ovalbumin, rabbit albumin, human albumin, and gelatin) were equally effective competitors for adsorption sites on plastic. Nonionic detergents (Tween 20, and Triton X-100) were strong competitors even at 10:1 competitor-to-antigen ratios. In antigen capture assays, normal serum components blocked attachment of antigen-specific IgG, but this competition could be lessened to a degree by the use of strongly binding polystyrene plates. In indirect ELISA for measurement of serum antibody, the use of antigenic mixtures gave significantly lower antibody titers when the desired antigen was less than 1% of the total protein coated. Therefore, the use of mixed or crude antigens in ELISA presents significant problems concerning the sensitivity and specificity of tests.

Quantitation of apolipoprotein E in rabbit sera with a competitive enzyme-linked immunosorbent assay

A competitive enzyme-linked immunosorbent assay was developed to quantitate apoE levels in normal and cholesterolemic rabbit serum. The assay can detect 1 ng of apoE and has an interassay coefficient of variation of 5.1%. The assay's antigen specificity was established by the generation of a competitive displacement curve with rabbit apoE, but not with rabbit albumin nor with rabbit apoC. Nonimmune serum was not able to produce a detectable response in the assay. Lipid-protein interactions did not interfere with the assay and color development was linear throughout the incubation time. Rabbits fed a normal diet had 5.3±0.4 mg of apoE/dl serum. Rabbits fed a diet containing 1% (w/w) cholesterol for 14 days had 86±11 mg of apoE/dl serum.

Transmural [ 125I]albumin concentration in the rabbit aorta during acute hypoxia

We have quantified the concentration profile of 121I-labeled rabbit albumin in the avascular intima and media of the rabbit descending thoracic aorta following intravenous injection under control and acute hypoxic conditions in vivo. Our purpose was to determine if alterations occurred in the transmural concentration profiles which could be attributed to hypoxia-induced changes in the permeability of the intimal endothelium to plasma-borne macromolecules. The profiles were obtained with frozen serial sections of the aorta from experiments of 30 min duration. Acute hypoxia was induced by addition of nitrogen to the breathing mixture. The hypoxia resulted in arterial pO 2 values of 23–32 mm Hg while the arterial pO 2 in the control animals ranged from 80 to 88 mm Hg. All animals were under sodium pentobarbital anesthesia. The results revealed no detectable changes in the concentration profile in the inner media accompanying hypoxia. However, increases in the label concentration in the outer media of the hypoxic animals suggested either dilation or increased permeability of the adventitial blood vessels.

Comparison of the effects of glucocorticoid and indomethacin treatment on the acute inflammatory reaction in rabbits

We have recently shown that indomethacin and ASA diminish the elevated blood flow, protein exudation, and leukocyte infiltration during acute inflammation induced by killed Escherichia coli, the reversed Arthus reaction, or zymosan-activated plasma (ZAP; C5ades-arg) in rabbit skin. All of these effects were likely due to the inhibition by these drugs of prostaglandin (PG) synthesis in the lesions. Because glucocorticoids are also reported to inhibit PG production and, in large doses, to suppress inflammation accompanying various clinical conditions, we investigated the effects of hydrocortisone (HC), and methylprednisolone (MP), administered in large doses (100 mg/m2/d of MP or 2.5 g/m2/d of HC) on the above three forms of acute inflammation in rabbits. The effect of indomethacin treatment was studied in parallel for comparison. Blood flow, protein exudation, and leukocyte infiltration were quantitated simultaneously with 86Rb Cl, 125I-labelled rabbit albumin and 51Cr labelled blood leukocytes. Systemic indomethacin therapy decreased the blood flow and permeability, while local indomethacin (2.5 μg) significantly inhibited leukocyte infiltration into the lesions. In contrast, HC and MP caused only a mild decrease in blood flow, without altering protein exudation or leukocyte influx. However, HC and MP did inhibit protein exudation induced by bradykinin or histamine injection. These results indicate that, at least in rabbits, HC and MP, in contrast to indomethacin, have very weak anti-inflammatory actions on three complement- and neutrophil-mediated inflammatory responses, i.e., E. coli, ZAP (C5ades-arg) and reversed Arthus reactions.

Tissue sites of catabolism of albumin in rabbits.

The sites of albumin catabolism were determined in rabbits using [14C]sucrose-labeled rabbit albumin. The [14C]sucrose moiety is not degradable and accumulates in tissues degrading the protein. Albumin was labeled with [14C]sucrose, and the monomeric form was selected for injection into rabbits. The validity of the sucrose-labeled albumin as a tracer for native albumin was shown by the similar plasma decay kinetics of 125I-labeled albumin derivatized with sucrose and 131I-labeled native albumin and by the similar decay kinetics for the biologically screened and unscreened preparations of [14C]sucrose-albumin. Two days after injection of [14C]sucrose-albumin, tissues were assayed for accumulated 14C-labeled degradation products soluble in trichloroacetic acid. All tissues catabolized albumin with no tissue of predominant importance; liver, kidney, and muscle were the largest contributors. Expressed in terms of activity per unit wet weight, adrenal, kidney, spleen, ovary, bone marrow, and liver were the most active. These most active tissues are those with fenestrated or discontinuous capillary beds, suggesting that exposure to high concentrations of albumin is an important determinant of their high rates of albumin degradation.

Intravenous albumin administration in acid aspiration syndrome in rabbits.

The possible value of albumin in a rabbit model of the acid aspiration syndrome was studied. Hydrochloric acid was instilled into the respiratory tracts of three groups of rabbits: Group A received a high intravenous dose of human albumin (1.5 gm/kg body weight); Group B (control) was given Hartmann's solution, and Group C a low dose of albumin (0.25 gm/kg body weight). The total amount of intravenous fluids was identical in all groups. Serum and pulmonary edema fluid (PEF) concentrations of total protein were highest in Group A. Simultaneous concentration gradients between serum and PEF for total protein, human and rabbit albumin, and globulin fractions were not statistically different in the three groups. In Group A, PEF appeared first and PaO2, static compliance, and hematocrit decreased significantly more than those of the two other groups. Survival of animals in Group C was highest. An additional Group (D) of rabbits received the same high dose of albumin without acid aspiration. In Group D hematocrit decreased while serum total protein and pulmonary function remained unchanged. It seems that a high dose of albumin causes a further deterioration of lung function following acid aspiration because of extravasation into the interstitial space. The administration of low doses of albumin was not different than Hartmann's solution, but led to the best survival in our model.

Relationship Between Progesterone and Egg Production in Pheasants

A radioimmunoassay was developed to measure progesterone concentration in sera of immature and mature female pheasants. The antiserum to progesterone was produced against progesterone-3-carboxymethyloxime: bovine serum albumin in female rabbits. Crossreactivity of the antiserum with 17 different steroids was tested and was less than 2% for all steroids except 5α-pregnane-3,20-dione (18%) and pregnenolone (9%). Sensitivity of the standard curve was 2.7 pg. The within and between assay coefficients of variation were 7% and 14%, respectively.Blood samples were collected weekly starting when the birds were 17 weeks of age and continued until they were 1 year of age. Progesterone concentration was measured in all serum samples. Egg production was recorded daily for the individual hens. The relationship between progesterone concentration and egg production was studied.Average progesterone concentration prior to sexual maturity was significantly lower than at subsequent ages. There was a significant positive correlation between average progesterone concentration and average percent egg production within individual birds. Furthermore, statistically a significant amount of the variation in percent egg production was explained by differences in progesterone concentration. These results indicate that progesterone is important for egg production in pheasants, as it is in chicken and turkey hens.

EFFECT OF TIMEPIDIUM BROMIDE, AN ANTICHOLINERGIC AGENT, ON GASTRIC AND DUODENAL BLOOD FLOW DISTRIBUTION IN RABBITS

Effects of timepidium bromide (TB; anticholinergic agent), acetylcholine (ACh) and neostigmine (Neost) on gastric and duodenal blood flow distribution were studied by the use of 131I-labeled macro-aggregated human serum albumin (MAA) in rabbits. In normal rabbits, gastric blood flow was found to be uneven in various regions of the stomach: anterior corpus (50% of total gastric blood flow)>posterior corpus (40%) > pyloric antrum (7%). Intravenous administration of TB (200 μg/kg) to normal rabbits produced a slight increase in total gastric blood flow, but the increase in the mucosal layer of the pyloric antrum was considerable. On the other hand. ACh (10 μg/kg, i.v.) and Neost (50 μg/kg. i.v.) significantly reduced the total gastric blood flow, in particular, the mucosal blood flow in the anterior and posterior corpus. This reduction in blood flow was virtually abolished by TB and was restored to the normal level. These results suggest that these cholinergic or anticholinergic drugs affect the gastric blood flow and that these effects may be mediated through muscarinic receptors. Blood flow in the duodenum was only slightly changed by these drugs.

Sodium dodecyl sulfate acrylamide gel electrophoretic studies on low-molecular-weight proteinuria, an early sign of cadmium health effects, in rabbits.

Sodium dodecyl sulfate (SDS) acrylamide gel electrophoretic studies were performed on low-molecular-weight (LMW) proteins in urine from rabbits given sub-cuteneous injections of cadmium chloride at a dose level of 0.5mgCd/kg over a period of 42 weeks to evaluate the procedure for screening early effects of cadmium : in the 1st week, a gradual increase in urine cadmium was found ; in the 3rd week, slight LMW proteinuria (proteins of MW 12, 000 and 25, 000); in the 6th week, slight protein-uria, (proteins mostly of MW 67, 000); in the llth-13th week, aminoaciduria, glycos-uria, proteinuria and LMW proteinuria (proteins of MW 12, 000 and 25, 000). As shown above, protein of MW 12, 000 (probably β2-microglobulin) and 25, 000 (pro-bably retinol-binding protein) increased in urine a little earlier than protein of MW 67, 000 (probably albumin) in rabbits given cadmium. Therefore, urine LMW pro-teins were thought to be effective indices for screening early effects of cadmium.Sixty-80% of proteins in urine from rabbits given cadmium were proteins of MW 67, 000, while only 10% were LMW proteins. This fact might suggest that cadmium affect tubules as well as glomerules.

Effect of timepidium bromide, an anticholinergic agent, on gastric and duodenal blood flow distribution in rabbits.

Effects of timepidium bromide (TB; anticholinergic agent), acetylcholine (ACh) and neostigmine (Neost) on gastric and duodenal blood flow distribution were studied by the use of 131I-labeled macroaggregated human serum albumin (MAA) in rabbits. In normal rabbits, gastric blood flow was found to be uneven in various regions of the stomach: anterior corpus (50% of total gastric blood flow) greater than posterior corpus (40%) greater than pyloric antrum (7%). Intravenous administration of TB (200 microgram/kg) to normal rabbits produced a slight increase in total gastric blood flow, but the increase in the mucosal layer of the pyloric antrum was considerable. On the other hand, ACh (10 microgram/kg, i.v.) and Neost (50 microgram/kg. i.v.) significantly reduced the total gastric blood flow, in particular, the mucosal blood flow in the anterior and posterior corpus. This reduction in blood flow was virtually abolished by TB and was restored to the normal level. These results suggest that these cholinergic or anticholinergic drugs affect the gastric blood flow and that these effects may be mediated through muscarinic receptors. Blood flow in the duodenum was only slightly changed by these drugs.

The hexa- and pentapeptide extension of proalbumin II. Processing of specific antibodies against the synthetic hexapaptide

The chemically synthesized proalbumin hexapeptide was coupled to rabbit albumin with carbodiimide. Subsequently rabbits were immunized by subcutaneous injection of the conjugate. After 5 weeks the rabbits had developed antibodies against the hexapeptide, which could be detected by immunodiffusion. A sensitive enzyme-linked immunosorbent assay was developed. Using the hexapeptide and other very similar peptides as antigens, a high specificity of the antibodies against the proalbumin hexapeptide was found.

Specificity of anti-albumin autoantibodies in liver diseases

The reaction between glutaraldehyde-treated human albumin and the anti-albumin autoantibodies found in sera of hepatic patients was inhibited by: (1) peptides with a molecular weight around 10,000 daltons which were isolated from the pronase digest of glutaraldehyde-polymerized human albumin, (2) pyridinium compounds resulting from the reaction of glutaraldehyde with the amino groups of 6-aminohexanoic acid, and (3) other glutaraldehyde-treated proteins (rabbit albumin, bovine albumin, ovalbumin, peroxidase, human gamma globulin). Our results suggest that the anti-albumin autoantibodies recognize on glutaraldehyde-treated human albumin the new antigenic determinants containing at least partly pyridinium-like structures. This type of structure could also occur in vivo, in circulating albumin molecules, by inter- and intramolecular cross-linking reactions between aldehydic groups which appear by oxidative deamination and ε-amino groups of lysine residues, thus leading to non-self albumin which stimulates the synthesis of autoantibodies.

Albumin-immunoglobulin complexes in human serum: classification and immunochemical analysis.

A complex between serum albumin and immunoglobulins was observed on immunoelectrophoresis in six patients. Two patients with multiple myeloma had monoclonal IgA-albumin complexes; one of these complexes was formed by covalent bonds and the other by non-covalent bonds. Four patients displayed non-covalent IgG-albumin complexes: of these, one had multiple myeloma, two had been treated with nitrofurantoin for prolonged periods, and one had diabetes mellitus. The IgG-albumin complex of the last patient was subjected to a detailed immunochemical analysis. The albumin-specific antibodies were isolated by affinity chromatography and analysed, using a sensitive tritium labelling technique. The antibodies were polyclonal, complexed with serum albumin through their Fab portion, and showed a high specificity for the human albumin as compared with bovine and rabbit albumins. The serum albumin of two patients displayed an abnormal behaviour in reduced SDS-polyacrylamide gel electrophoresis (PAGE). The abnormal albumins had an apparent molecular weight of 52,000 and could react with rabbit anti-human serum albumin like the normal protein. No abnormal albumin could be detected in 20 other patients' sera, including nitrofurantoin-treated patients and normal controls. These findings suggest a possible role for an altered self-component in the triggering of a specific autoimmune reaction.

Antibody-induced foot oedema, hyperalgesia and monoarticular arthritis in rats, guinea-pigs and rabbits for testing anti-inflammatory, antiarthritic agents.

To develop a simple and convenient test based on immunologic events that can be used for testing anti-inflammatory antiarthritic drugs, experiments were performed on rabbits, guinea-pigs and rats. A monoarticular arthritis was provoked injecting a knee joint with: (a) ovalbumin or bovin serum albumin (BSA) in immunized rabbits (active immunization); (b) rabbit anti-BSA serum in rabbits previously treated i.v. with BSA (passive immunization); (c) rabbit anti-guinea-pig or anti-rat serum in normal guinea-pigs and rats. The diameter of the joint was measured with a caliper. The development of the joint swelling was found to be favourably influenced by anti-inflammatory drugs given orally or intra-articularly. The test was considered suitable but not practical for testing a large number of compounds. Foot oedema and hyperalgesia were provoked by injecting rabbit anti-rat serum into the food pad of normal rats. Volume and sensitivity to a nociceptive stimulation (compression) were determined. Steroidal and non-steroidal anti-inflammatory drugs and miscellaneous drugs were tested orally in a preventive-type schedule of treatment. The test was found suitable for testing large number of compounds. The results were compared to the results obtained testing the same compounds against foot oedema and hyperalgesia provoked by carrageenan. Some of the drugs tested modified foot swelling and hyperalgesia differently in the two experimental models of inflammation.

Vitamin D plasma binding protein. Turnover and fate in the rabbit.

The metabolic disposition of the plasma binding protein (DBP) for vitamin D and its metabolites was studied in adult rabbits. Apo-DBP was purified from rabbit plasma and enzymatically labeled with radioiodine. The radioiodine-labeled protein retained its ability to bind vitamin D sterols and its physicochemical properties. When 125I-labeled DBP and 131I-labeled rabbit albumin were simultaneously injected intravenously, the 125I was cleared from plasma at a faster rate (t 1/2 = 1.7 d) than 131I (t 1/2 = 5 d) and 125I was present in excess of 131I in kidney, liver, skeletal muscle, heart, lung, intestine, testis, and bone 1 h after injection. In contrast to DBP, 25(OH)D3 was cleared more slowly (t 1/2 = 10.7 d). Compared to albumin, DBP radioactivity appeared earlier and in greater quantity in the urine of catheterized rabbits. Gel filtration analyses of plasma revealed most of the 125I to elute in the position of DBP, with only small amounts in the less than 1,000-dalton region. In contrast, almost all of the urine 125I eluted in this small molecular weight fraction. The molar ratio of DBP to 25(OH)D3 in normal rabbit plasma was 138/1. The extravascular pool of DBP was calculated to be 1.5-2.4 times larger than the intravascular DBP pool, and the molar replacement rate of DBP was 1,350-fold higher than that of 25(OH)D3. The plasma disappearance curves of holo-DBP, prepared either by saturating with 25(OH)D3 or by covalently linking 3 beta-bromoacetoxy-25(OH)D3, were very similar to that of apo-DBP. Neuraminidase treatment of DBP did not alter its plasma survival. These studies indicate that DBP or DBP-25(OH)D3 complex is removed from plasma by a variety of tissues, that the DBP moiety is degraded during this process, and that a significant recirculation of 25(OH)D3 probably occurs. The molar excess of DBP to 25(OH)D3 in plasma, and the relatively rapid turnover of DBP indicate that a high capacity, high affinity, and dynamic transport mechanism for vitamin D sterols exists in rabbit plasma.

Antigenic specificity of glutaraldehyde-treated rabbit albumin

Rabbit albumin treated with glutaraldehyde is immunogenic in rabbits due to the new antigenic determinants induced into the molecule by glutaraldehyde (Onicǎ et al., 1978 a, b). Hardy et al. (1976 a, 1977) isolated quaternary pyridinium compounds from the acid hydrolysis products of glutaraldehyde-reacted ovalbumin, which are responsible for the strong chromophore absorbing at 265 nm exhibited by glutaraldehyde-treated proteins. Our data have shown that such structures are involved in the antigenic determinants of glutaraldehyde-treated rabbit albumin. As a consequence, the reaction between the modified albumin and the specific antibodies is inhibited by: (1) peptides with molecular weights of 7800 and 11,000 daltons, and having an absorption maximum at 265 nm, isolated from the pronase digest of glutaraldehyde-treated albumin; (2) compounds with pyridinium structures obtained by the reaction of glutaraldehyde and the amino groups of 6-aminohexanoic acid and (3) other proteins (human and bovine albumin, ovalbumin, rabbit immunoglobulin G, peroxidase) treated with glutaraldehyde. Since glutaraldehyde-treated albumin shows a reaction of identity with albumin aged in vivo or in vitro, it is possible that the physiologic aging of albumin involves the formation of pyridinium-like structures. The molecular rearrangements around such structures may represent the new antigenic sites specific for the aged albumin. These sites could be recognized as non-self by the immunocompetent cells, stimulating the production of physiologic autoantibodies which remove the modified albumin from the circulation.