Enhanced induction of plasma interferon after subcutaneous administration in rabbits of poly ICLC with albumin

Intravenous administration of poly ICLC in rabbits yields very high plasma interferon (IFN) levels; dosages from 250 to 1000 micrograms/kg body weight are very toxic. Subcutaneous administration of poly ICLC together with a high concentration of human serum albumin potentiates the inducer activity in comparison to poly ICLC in saline. Finally, a dosage of 50 micrograms of poly ICLC in 12% serum albumin is more effective as an IFN inducer than other dosages.

The lymphatic route. V. Distribution of human natural interferon-beta in rabbit plasma and lymph

Human natural interferon-beta (HuIFN-beta) was administered through different routes (intravenous [i.v.], intramuscular [i.m.], and subcutaneous [s.c.]) and its distribution in lymph and plasma was evaluated. After i.v. (bolus) administration the lymph/plasma ratio was about 0.35 but it significantly increased (11-fold) after i.m. administration. Addition of human albumin (ALB) to the IFN solution did not favor IFN absorption through the lymphatics. On the other hand, addition of ALB improved IFN absorption through the lymphatics after s.c. administration. These results are interesting because they clarify why IFN-beta can exert immunomodulatory activities in spite of very low plasma levels.

The lymphatic route. VI. Distribution of recombinant interferon-alpha 2 in rabbit and pig plasma and lymph

Human recombinant (R) interferon-alpha 2 (either cold or labeled with 125I or 131I) has been administered through different routes [intravenous (i.v.), intramuscular (i.m.), and subcutaneous (s.c.)] and its distribution in lymph and plasma has been evaluated in rabbits and pigs. After i.v. (bolus) administration, the lymph/plasma ratio was about 1. After s.c. and i.m. administration, the ratio varied from an average of 0.8 up to 2, respectively, indicating that R interferon-alpha 2 is preferentially absorbed via lymphatics when injected into the shank muscles. Another novel result is that the ratio is markedly increased after s.c. administration of interferon-alpha 2 with a solution containing 12.5% human albumin. In this case, albumin acts as an interstitial fluid expander, thereby increasing the fluid pressure and favoring lymphatic absorption. Similar results were obtained using either cold or labeled interferons in rabbits; moreover, the effect of albumin was confirmed in the pig by simultaneously injecting 131I-interferon (in saline) and 125I-interferon (in albumin solution) in the left and right subcutis of the shanks, respectively. All of these data suggest that the indirect lymphatic route is a feasible proposition, and that by modifying the absorption, the distribution and fate of interferon may improve the therapeutic index of biological response modifiers.

DNA synthesis and interferon release by human peripheral lymphocytes exposed to high potassium medium

Lymphocytes have their membrane potential changed during transition from the resting to the active state. On these grounds, we investigated the response of human peripheral lymphocytes to a depolarizing high-potassium (102.7 mM) medium, by assaying cellular incorporation of labeled thymidine and interferon (IFN) release in the culture medium. The greatest effect is evident 3-4 days after preincubation for 120 min in high K+ medium. A temporal correlation has been observed between rate of DNA synthesis and IFN production. The IFN activity is shown to be gamma-type.

The physiological interferon response. V. Antiviral activity present in rat lymph is neutralized by anti-mouse interferon-gamma antibodies

By neutralization tests using anti-rat and mouse interferon (IFN) antibodies, we tested whether the antiviral activity present in abdominal lymph but absent in plasma of healthy rats, could be ascribed to IFN. Antimouse IFN-gamma antibodies neutralized the inhibitor completely while anti-rat IFN-alpha/beta antibodies did not. We conclude that rat lymph contains traces of IFN-gamma and that the antiviral activity is not due to low-density lipoproteins, immunoglobulins, or to cell-produced viral inhibitors. This finding extends previous observations on rabbit lymph and further supports the existence of a physiological low-level interferon response.

The physiological interferon response: IV. Production of interferon by the perfused human placenta at term

Human placentas at term, free of bacterial and viral diseases, have been perfused and maintained sterile for up to 13 hr. Several parameters indicate that the organs remained viable and released interferon into the perfusate in a progressive fashion. The amount of interferon was small and the individual variations indicate that there are "poor" and "good" placenta producers. Both interferons -alpha and -beta were produced with a prevalence of the latter type. The partial acid lability and the type heterogeneity suggest that under physiological conditions the placentas produce unusual interferons, the function of which remains speculative.

Effect of exercise on plasma interferon levels

The effect of exercise on plasma interferon activity was studied on eight male subjects before and after exercise on a bicycle ergometer for 1 h at 70% of their maximal O2 consumption (VO2 max). Acid-labile interferon, alpha-type according to immunological characterization, rose significantly from a preexercise value of 3 +/- 1 to 7 +/- 2 IU/ml postexercise. Negligible changes were recorded for plasma protein, lipid, and glucose concentrations, whereas blood lactate slightly increased only at the end of exercise. According to hematocrit and plasma protein values before and after exercise, hemoconcentration did not occur. These data provide evidence that plasma interferon activity increased following a bout of submaximal exercise.

Catabolic sites of human interferon-gamma

Recombinant human interferon-gamma (HuIFN-gamma) injected into rabbits disappeared from the circulation more rapidly than natural IFN-gamma. The latter displayed an initial decay curve more rapid than that for natural HuIFN-alpha although 4 h after injection plasma levels were similar. This result suggests that IFN-gamma has pharmacokinetic properties different to those of IFN-alpha which may be explained by considerable and simultaneous hepatic and renal catabolism. Surprisingly, the hepatic uptake of recombinant (unglycosylated) IFN-gamma was more marked than uptake of natural IFN-gamma. Moreover, both IFN-gamma preparations were cleared by the isolated and perfused kidney and once again the recombinant IFN disappeared more rapidly. This result does not conform with the suggestion that IFN-gamma exists as a tetramer which would not be filtered by the glomerulus, but is consistent with the pharmacokinetic behaviour shown in vivo.

Interferon production in BCG-sensitized rabbits challenged with PPD

Intravenous administration of PPD into BCG-primed rabbits results in the release of IFN into the circulation. Peak interferon titres occur in plasma 1 h after PPD injection, rapidly decline during the following 3 h and depend on the dose of tuberculin administered. Bilateral nephrectomy of BCG-primed rabbits challenged with PPD affects remarkably the disappearance of IFN from the circulation. Characterization of the BCG-PPD-induced IFN shows that it is heat-labile, is almost completely inactivated after dialysis at pH 2 and displays a remarkable cross-species activity, particularly on human cell lines.

Pharmacokinetics of human lymphoblastoid interferon in rabbits

By intravenous (bolus) administration of large amounts (29 Mega Units) of lymphoblastoid interferon into rabbits, it has been possible to detect circulating antiviral activity (0.02% of the dose) up to 18 hr post-injection and to determine for the first time the pharmacokinetic parameters. The slow component (elimination phase) has a half-life of 235 +/- 9 min. The total apparent volume of distribution is 2,564 +/- 1,497 ml which is far larger than the combined plasma-extracellular volumes. This suggests a IFN dilution due to its extensive binding to cell receptors. The clearance of 7.3 +/- 4.1 ml/min is an index of the rate of renal and cellular (internalization of the receptor-ligand complex) catabolism of IFN. Pharmacokinetic parameters are useful for devising an administration schedule of IFN as an antiproliferative agent but are not predictive of an immunological response if IFN is used as an immuno-adjuvant.

Pulmonary catabolism of interferons: alveolar absorption of 125I-labeled human interferon alpha is accompanied by partial loss of biological activity

The catabolism of interferon was examined in isolated rabbit lungs which were ventilated and perfused with homologous blood. Natural human interferon-alpha (HuIFN-alpha) from lymphoblastoid Namalwa cells or recombinant DNA-derived HuIFN-alpha 2 were labeled with 125I, mixed with an excess of the respective cold interferons and added to the perfusion blood. Protein-bound and acid-soluble radioactivity, as well as antiviral activity, were measured at regular time intervals. During the first 3 h of perfusion, only very small fractions of the interferons disappeared from the perfusate, irrespective of whether lungs were inserted in the perfusion system. This indicated that catabolism of interferons in the pulmonary circulation was negligible. On the other hand, when the interferons were instilled into the bronchial-alveolar tree, absorption of antiviral activity differed from that of acid-precipitable protein-associated radioactivity. While most of the radioactivity was transferred into the perfusate, only 2% of antiviral activity of natural HuIFN-alpha and 30% of that of HuIFN-alpha 2 were recovered in the perfusate. In both cases acid-soluble radioactivity in the system reached about 10%. Since radioiodide, instilled in the bronchial-alveolar tree, was transported rapidly into the perfusate, this type of analysis did not help in locating the site(s) of degradation. Alveolar macrophages did not catabolize or inactivate interferons in vitro.

The physiological interferon response. II. Interferon is present in lymph but not in plasma of healthy rabbits

If interferon is produced by the gut-associated lymphoid tissue of healthy rabbits under normal conditions and is not all bound in situ, it may spill over and be detectable in lymph. We therefore measured antiviral activity in lymph and plasma simultaneously. We found that antiviral activity was consistently measurable in abdominal and thoracic lymph but not in plasma or in the lymph collected from the hind leg duct. The antiviral activity was neither due to lipoproteins, nor immunoglobulins, nor to cell-produced viral inhibitors other than interferons. Extensive characterization of the antiviral activity indicated that the inhibitor is either rabbit interferon gamma or an acid-labile interferon alpha or a mixture; appropriate antisera will be necessary to resolve this uncertainty. The results support the view of the existence of a physiological interferon response.

Degradation of human 125I-interferon alpha by isolated perfused rabbit kidney and liver

Rabbit livers and kidneys were isolated and perfused with homologous blood. After equilibration, human IFN alpha labeled with 125I and an excess of cold IFN alpha were added, and blood samples were withdrawn at predetermined times. Protein-bound and acid-soluble radioactivity together with biological (antiviral) activity were measured. Our results show that although liver exerts a minimal catabolism, the kidney filters and breaks down a considerable amount of IFN alpha. The parallelism between protein-bound radioactivity and biological activity decay curves indicates that IFN carefully labeled with 125I can be reliably used for metabolic investigations.

The role of liver in the catabolism of human alpha- and beta-interferon

The susceptibility of human leukocyte (alpha), fibroblast (beta) and recombinant alpha-2-interferons to clearance by the isolated and perfused rabbit liver has been evaluated. Human leukocyte and recombinant alpha-2-interferons were stable and their initial levels were maintained in the perfusate even if they had been treated with neuraminidase, thus suggesting that alpha-interferons have no exposed sugars recognizable by hepatic binding proteins. On the other hand, native, and particularly desialylated human beta-interferon, underwent marked hepatic uptake confirming the importance of the liver as a catabolic site for glycosylated interferons.

The kidney is the main site of interferon catabolism

The fate of human natural interferons alpha and beta and of recombinant (R) alpha 2 has been investigated by using an isolated and perfused rabbit kidney preparation with a normal physiological performance. A remarkable amount of IFN is filtrated in a monoexponential fashion, reabsorbed and very likely degraded in tubular cells with negligible excretion in the urine. The disappearance rate of HuRIFN-alpha 2 is higher than natural HuIFNs-alpha and beta and is in keeping with the lower molecular weight of RIFN-alpha 2. Differences in molecular charge or shape are probably responsible for the slightly reduced filtration of IFN-beta. Pharmacokinetic studies in animal models appear instructive and useful for devising improved dosage schedules in clinical trials.

Cyclic changes of sialidase in human cervical mucus

1. Sialidase activity is detectable in whole cervical mucus of normal women throughout the menstrual cycle and presents cyclic variations toward endogenous and exogenous substrates. 2. The level of sialic acid bound to the mucus increases progressively till mid-cycle and declines in the post-ovulatory phase. 3. The sialidase of the mucus probably derives from different sources and its role remains speculative.

Renal metabolism of rabbit serum infection

Three different approaches have been used to evaluate the catabolism of rabbit serum interferon (IFN) by the kidneys. Firstly, in normal rabbits the disappearance of exogenous IFN from plasma was very rapid, whereas it was significantly slower after bilateral nephrectomy. Secondly, the IFN level in arterial blood was always higher than in renal venous blood: the mean renal extraction rate of IFN in the rabbit, with a renal plasma flow of 9 ml/min, was about 1 ml/min. Thirdly, a selective and reversible tubular damage induced by maleate before intravenous administration of IFN significantly inhibited luminal uptake of IFN and markedly increases the interferonuria. All of these results support the view that the kidneys have a preponderant role in IFN filtration, catabolism and excretion.

Renal filtration, absorption and catabolism of human alpha interferon

The renal handling of human interferon-alpha has been evaluated by using an isolated and perfused rabbit kidney. IFN-alpha disappears from plasma with a t1/2 of 81 min and the fractional turnover rate is 0.84%/min. About 47 molecules of IFN-alpha are filtrated with 100 molecules of creatinine but most of the IFN is absorbed by tubular cells. This is the first report showing that human IFN-alpha is filtrated by the kidney, largely absorbed, most probably catabolized within tubular epithelium and excreted in negligible amounts with the urine.

Studies of factors regulating the ageing of human erythrocytes--III. Metabolism and fate of erythrocytic vesicles

1. Ageing erythrocytes release vesicles the metabolism of which is unknown. 2. Human and rat erythrocytic vesicles labelled with 51Cr and injected into rats, disappear very rapidly from the circulation with half-lives from 2 to 8 min. 3. Their lifetime resembles that of liposomes encapsulating [51Cr]haemoglobin (Hb) and in both cases, liver and spleen take up considerable amounts of radioactivity. 4. These results indicate, for the first time, that vesicles released from erythrocytes are cleared at very fast rates from the circulation and suggest that this may be the reason for the absence of vesicles in the plasma in vivo.

Studies of factors regulating the ageing of human erythrocytes. II. Metabolic depletion of erythrocytes is not accompanied by a decrease of their sialic acid content during blood bank storage

Erythrocytes from human blood stored at 5 degrees C in anticoagulant-preservative solutions are considered, after a period from 21 to 24 days, unsuitable for transfusion. The nonviability of the cells appears due to metabolic impairment accompanied by a change of the biophysical properties of the cell but surprisingly not to a decrease of sialic acid of the membrane. The absence of proteolysis can be attributed to calcium chelation and to the stable levels of plasma protease inhibitors throughout the storage period. In fact, when erythrocytes are incubated for several days at 5 degrees C in protein-free media, release of sialopeptides from the membrane increases slowly and steadily, particularly if the medium is without glucose and adenine but contains divalent cations. Moreover, this phenomenon is strikingly amplified when incubation in protein-free media is carried out at 37 degrees C and once the ATP level has fallen below 5% of its initial value.