Physical, morphological, and biochemical alterations in the membrane of AKR mouse cells after interferon treatment

Intralesional Beta-Interferon Treatment of Cervical Intraepithelial Neoplasia Associated with Human Papillomavirus Infection

Aims and backround

Interferons (IFN) have offered considerable advances in the therapy of genital warts even those associated with cervical intraepithelial neoplasia (CIN); intralesional therapy either alone or in combination with other modalities such as cryosurgery and laser surgery provides improved clearing and cure of these often recalcitrant lesions. The purpose of this study was to evaluate the effectiveness of intralesional IFN therapy in patients with CIN associated with human papillomavirus (HPV) infection.

Methods

Beta-IFN was injected intra-perilesionally into the cervix in 41 patients with CIN associated with HPV infection.

Results

The regimen of 3 million international units (IU) injected intralesionally daily in the 1st week and 3 times a week in the 2nd and 3rd weeks for a total of 11 injections and a total dosage of 33 million IU yielded an 80 percent cure rate and may be more advantageous than other treatment options in certain instances. Cytocolposcopic and histologic examination was carried out before and after treatment and 24 lesions were also analyzed for type-specific papillomaviruses using in situ DNA hybridization. CIN disappeared in 33 patients 6 months after the end of therapy. Side effects of intralesional IFN therapy are dose related and for the most part readily tolerated.

Conclusions

Intralesional IFN proved to be effective treatment for CIN associated with HPV infection (cure rate: 80%) and well accepted because hospitalization is not required and no important side effects occur.

Effects of human interferon preparations on neutrophil function

We have studied effects of two partially purified human leukocyte (alpha) interferon (IFN) preparations (PIF-A and PIF-B) and a highly purified fibroblast (beta) IFN on the functional activity of normal human neutrophils (PMNs). In vitro, PIF-B conferred a significant and dose-dependent enhancement of chemiluminescence (CL) induced both by phagocytosis and a soluble stimulus, f-Met-Leu-Phe, and decreased killing of Staph. aureus. In contrast, PIF-A caused only a slight inhibition of bactericidal activity and had no effects on CL. beta-IFN had no effects on either bactericidal activity or CL. Migration under agarose was decreased with all of the IFN but phagocytosis and release of enzymes was not affected. PMNs from seven patients treated with PIF-A for multiple myeloma exhibited increased CL responses but no other PMN functions were affected. The findings that human IFN preparations affect PMN functions indicate that high-dose IFN therapy of immunocompromised patients should be carefully evaluated for the possibility of increased infectious complications.

Local cutaneous necrotizing lesions associated with interferon injections

Long-term i.m. or s.c. injections of interferon-alpha, beta, and gamma(IFN) in patients with chronic myelogenous leukemia (CML) can cause severe, long-lasting cutaneous complications consistent with necrotizing vasculitis. The purpose of this study was to describe the cutaneous lesions and the course of illness in 7 well-documented patients with Philadelphia chromosome-positive (Ph+) CML treated with IFN. We reviewed 7 patients diagnosed with Ph+ CML at M.D. Anderson Cancer Center between 1983 and 1994 who experienced cutaneous lesions at the injection site after treatment with i.m. or s.c. IFN (3 patients treated with IFN-alpha, 3 with combined IFN-alpha and IFN-gamma, and 1 with IFN-beta). According to pathology reports available for 3 patients, the cutaneous lesions seem to be consistent with necrotizing vasculitis. The skin reactions occurred independent of the IFN type, administration modality (i.m. or s.c.), duration of previously received IFN therapy (3-108 months), stage of disease, and cytogenetic response to IFN treatment. Of 7 patients, 4 developed low-grade fever during the occurrence of skin reactions, but all cultures taken from the abscesslike lesions were negative for bacterial or fungal infection. These lesions either did not resolve and required surgical debridement (5 patients) or resolved slowly with conservative management that included discontinuation of IFN at the specific, involved site. Independent of the IFN type or i.m. or s.c. injections, IFN can cause painful and long-lasting cutaneous lesions that frequently require surgical intervention. Whether this is a result of the high concentration of IFN at the injection site, the diluent, or an immunologic reaction remains unclear.

Interferon--a major regulator of natural killer cell-mediated cytotoxicity

Natural killer (NK) cells probably function as an early defense line against viruses because of their ability to kill virus-infected cells as well as a variety of tumor cells. In both cases, the killing is major histocompatibility complex (MHC)-unrestricted. NK cells exhibit spontaneous activity but they are positively regulated by interferons (IFNs) or indirectly by such IFN inducers as viruses, bacterial products, poly(rI):(rC), and mitogens. In addition to their "positive" regulation on NK activity, IFNs often act as "negative signals" for NK and lymphokine-activated killer (LAK) cell-mediated cytotoxicity. If NK susceptible target cells are exposed to IFN prior to NK cells, their sensitivity to NK activity is often markedly diminished. The mechanism by which IFNs (IFN-alpha, -beta, and -gamma) affect the sensitivity of target cells to NK activity remains unknown, but it is clear that this function is not shared by other cell-mediated killing processes. The protective effect induced by IFN against NK activity is dependent on new mRNA and protein synthesis and can be abolished when target cells are incubated with a combination of IFN and metabolic inhibitors or by chemotherapeutic purine or pyrimidine analogs. IFN treatment neither affects the conjugate formation between NK cell and target cell nor the susceptibility of target cells to NK cytotoxic factor (NKCF), released by effector cells. However, IFN reduces the capacity of target cells to induce activation of conjugated NK cells. Because IFN has the ability to induce or increase class I MHC antigen expression (on NK target cells), it has been suggested that class I MHC antigens act as "negative signals" or NK-mediated cytotoxicity. Although many studies support this hypothesis, others present evidence for a lack of involvement of class I MHC antigens in mediating sensitivity to NK activity. This review summarizes and discusses the dual effect of IFNs in the regulation of NK activity, the relationship between the expression of class I MHC antigens on target cell surface and sensitivity to NK activity following treatment with IFNs, and the possible clinical relevance of the dual effect of IFN.

Synergistic antitumor effects of carboplatin and interferons on hepatic metastases of colon carcinoma 26 and M5076 reticulum cell sarcoma

The effects of combination therapy including various antitumor agents and interferon on mice bearing hepatic metastases of colon carcinoma 26 were determined. Combined treatment with interferon-alpha A/D and carboplatin (CBDCA) was associated with a considerably more pronounced antitumor effect than was treatment with either drug alone. Murine interferon-beta and -gamma each also potentiated the antitumor activity of CBDCA. Combination therapy with interferon-alpha A/D and CBDCA also resulted in marked inhibition of hepatic metastasis of M5076 reticulum cell sarcoma. However, interferon-beta did not potentiate the antitumor activity of CBDCA against either subcutaneously implanted colon carcinoma 26 or pulmonary metastases of this tumor. Thus, in our model the combined administration of interferon and CBDCA was associated with a synergistic antitumor effect on hepatic metastases alone.

Use of Brefeldin A to localize block in intracellular transport of vesicular stomatitis virus G protein on interferon-treated cells

Brefeldin A (BFA) induced a rapid redistribution of vesicular stomatitis virus G protein (VSV-G) to the endoplasmatic reticulum (ER) in interferon (IFN)-pretreated cells. This result is consistent with accumulation of VSV-G in the trans-Golgi (GC) complex in cells pretreated with IFN and implies that IFN does not interfere with the ability of BFA to induce redistribution of proteins from GC to ER.

Interferon alpha (IFN)-macrophage interactions in human immunodeficiency virus (HIV) infection: role of IFN in the tempo and progression of HIV disease

Components of the host immune response that constrain virus replication and affect long-lasting antiviral immunity following HIV infection are incompletely defined. IFNs are critical participants in host antiviral processes. While IFN induces significant anti-retroviral activities, they also serve as harbingers for poor clinical outcomes. Moreover, monocytes, a major cellular source of IFN and HIV in man, are poor producer cells for IFN following HIV infection. Indeed, HIV infection of monocytes results in a diminished production and induction of IFN. IFN is only produced during cell to cell contact between HIV-infected cells and uninfected PBMC. Analysis of the biologic activity of HIV-induced IFN(s) shows that it poorly restricts HIV replication. Thus, the role of IFN in HIV disease is complex and seemingly paradoxical. The diminished capacity of HIV-infected monocytes to produce IFN and the production of defective IFNs likely reflect specific viral adaptive mechanisms for persistent infection.

Interferon-gamma-increased adherence of lymphocytes to high endothelial venules

Recirculating lymphocytes specifically adhere to and migrate through endothelium lining high endothelial venules (HEV), using specific and non-specific receptor-ligand systems. Interferons (IFN) profoundly affect the traffic of lymphocytes. Therefore the effects of interferon-gamma (IFN-gamma) on lymphocytes with respect to their interaction with HEV endothelium in lymph nodes were studied using the frozen section assay. In addition the organ-specificity of T- and B-lymphocyte adherence to HEV was investigated. Lymphocytes from spleen and peripheral lymph nodes showed increased binding to HEV of up to 35% compared to control lymphocytes after in vivo administration of IFN-gamma. The specificity of their binding did not change in terms of T:B-cell ratios. Increased adherence was also found by preincubation of lymphocytes with IFN-gamma in The enhanced binding was not due to increased expression of Mel-14 homing receptors and LFA-1 molecules on T and B lymphocytes, as shown by fluorescence-activated cell sorter analysis and antibody-blocking studies in the frozen section assay. Apparently IFN-gamma induces an additional Mel-14-independent and LFA-1-independent adhesion mechanism on lymphocytes.

Interferons modulate the expression of hormone receptors on the surface of murine melanoma cells

The effects of IFN-alpha, IFN-beta, and IFN-gamma on the differentiation of murine melanoma cells has been studied, in the presence and absence of melanocyte-stimulating hormone (MSH); the cells were highly responsive to treatment with MSH, which increased the rate of melanin production 25-fold and tyrosinase activity 6-fold within 4 d. Treatment of melanoma cells with IFN-alpha, IFN-beta, or IFN-gamma alone had no stimulatory effect on melanin production, but when the cells were cultured with IFN in the presence of MSH, pigment production was significantly and synergistically increased relative to cells cultured with MSH only. Flow cytometric analysis revealed that levels of tyrosinase in the cells were not affected by MSH or by IFN, which suggests that stimulation of melanogenic activity occurred by activation of a preexisting cellular enzyme. Scatchard analyses showed that the number of MSH receptors on IFN-treated cells was significantly increased (approximately 2.5-fold) relative to untreated cells (approximately 61,000/cell). These findings demonstrate that IFN stimulate differentiation (that is, pigmentation) of melanocytes by increasing the expression of surface MSH receptors; this in turn suggests that such a mechanism may in part be responsible for postinflammatory skin pigmentation, and provides an additional basis for action in the clinical responses of melanoma to IFN treatment.

Interferon-gamma-induced alterations of monocyte susceptibility to lysis by autologous lymphokine-activated killer (LAK) cells

Interleukin-2 (IL-2)-activated killer (LAK) cells specifically lyse human monocytes, which may account for some of the toxicity seen during LAK/IL-2 immunotherapy of cancer patients. In an effort to protect autologous monocytes, we treated monolayer cultures of monocytes with various doses of recombinant human interferon-gamma (IFN-gamma) and assessed their sensitivity to LAK-mediated lysis. IFN-gamma lessens the sensitivity of monocytes to lysis in a dose-dependent manner. Treatment of FMEX, an NK-resistant melanoma tumor cell line, with IFN-gamma did not affect its susceptibility to LAK lysis. Kinetic studies demonstrated that as little as 2 hr incubation with IFN-gamma was sufficient for protection to occur, and that monocytes which were treated with IFN-gamma for 2 hr, washed, and then cultured in medium alone retained their resistance to lysis for at least 4 days. Cold target inhibition studies showed that IFN-treated and untreated monocytes could effectively compete with each other for binding sites on LAK cells. Finally, binding studies demonstrated that there was no significant difference between the number of conjugates formed using either IFN-treated or untreated monocytes. This indicates that resistance to lysis induced by IFN treatment affects a post-binding event and not an initial recognition signal.

Differential activity of the 30-kD and the 100-kD forms of 2'-5'An synthetase induced by recombinant human interferon-alpha and interferon-gamma

Two molecular weight variants of the interferon (IFN)-induced intracellular enzyme 2',5'-oligoadenylate (2-5A) synthetase have been described recently; a 100-kD (cytoplasmic) and a 30-kD (intranuclear) form of the enzyme. The 30-kD form has been located primarily in the nucleus, while the 100-kD enzyme was found mainly in the cytoplasm. We examined 2-5A synthetase activity in extracts of human melanoma (Hs294t) cells treated with either recombinant (r) IFN-alpha A or rIFN-gamma to determine the differential regulation of these enzyme subtypes by treatment with the two types of IFN. Cells were treated (continuous exposure) with doses of rIFN-alpha A (1,000 U/ml) or rIFN-gamma (5,000 U/ml), each of which reduced the number of viable cells to 50% of control values (ED50) by day 3 of treatment. At equieffective doses, the maximal increase in 2-5A synthetase occurred at 48 h for both rIFN-alpha A and rIFN-gamma continuous exposure. The maximal 2-5A intracellular activities at 48 h were 800 +/- 40 and 160 +/- 15 nmoles/mg protein for rIFN-alpha A and rIFN-gamma treatment, respectively. High-performance gel permeation chromatography of cell lysates resolved the 2-5A activity into both 100-kD and 30-kD fractions. At 48 h after treatment with rIFN-alpha A, the activity of the 30-kD synthetase was approximately twofold greater than that of the 100-kD enzyme. In contrast, the activity of both 30- and 100-kD enzymes were equivalent 48 h after treatment with rIFN-gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma protects human thyroid epithelial cells against cell-mediated cytotoxicity

Interferons have been shown to have antagonistic effects on cell-mediated cytotoxicity. In the present study, we investigated various types of immunologically mediated cytotoxic reactions with a 51chromium release assay, using human thyroid cells as targets, which were cultured in the presence and absence of interferon-gamma (IFN-gamma). Antibody-dependent cell-mediated cytotoxicity (ADCC), natural killer (NK) cell-mediated cytotoxicity, and autologous lymphocyte-mediated cytotoxicity (ALC) were measured utilizing thyroid tissue, sera and lymphocytes from patients with autoimmune thyroid disease as well as from normal subjects. ADCC, determined with sera from patients with Hashimoto's thyroiditis, was reduced by 70% when the thyroid target cells were cultured in the presence of 1000 U human IFN-gamma/ml culture medium. Similarly, natural killer cell-mediated cytotoxicity, as well as autologous lymphocyte-mediated cytotoxicity, was significantly reduced after pretreatment of thyroid target cells with 500-1000 U IFN-gamma/ml culture medium. Although it is known that IFN-gamma renders target cells resistant to NK cell-mediated lysis, this is the first report on this effect using human epithelial cells, which may have major implications for the suggested role of IFN-gamma in the induction and perpetuation of autoimmune thyroid disease.

Modification of ribonucleotide and deoxyribonucleotide metabolism in interferon-treated human B-lymphoblastoid cells

The effect of recombinant interferon-alpha 2 (IFN-alpha 2) (50 U/ml) on the cell cycle, nucleotide metabolism, and protein and nucleic acid synthesis was studied in human B-lymphoblastoid (Daudi) cells. Cell cycle analysis showed that IFN treatment resulted in G0/G1 arrest (69%) as compared to control cells (42% at G0/G1). IFN inhibited the incorporation of radioactive thymidine and uridine into DNA and RNA, respectively, but had only slight effect on incorporation of radioactive threonine, leucine, or valine into proteins. IFN inhibited ribonucleotide biosynthesis by de novo and salvage pathways and decreased level of the P-ribose-PP. Both pathways of deoxyribonucleotide biosynthesis, ribonucleotide reduction and deoxyribonucleoside salvage, were also markedly inhibited by IFN., In contrast, ribonucleotide catabolism was significantly increased in the presence of IFN. No changes in ribonucleotide interconversion were found. Intracellular concentrations of both ribonucleotides and deoxyribonucleotides were markedly diminished by IFN. These results suggest that inhibition of both ribonucleotide and deoxyribonucleotide biosynthesis, together with increased rate of nucleotide catabolism, may significantly decrease intracellular nucleotide availability. Decrease of the supply of nucleic acid precursors, as well as limitation of nucleotides for energy metabolism and other processes, may result in the inhibition of cell multiplications.

Regulation of Moloney murine leukemia virus replication in chronically infected cells arrested at the G0/G1 phase

The replication of Moloney murine leukemia virus (MMuLV) in chronically infected mouse cells arrested at the G0/G1 phase of the cell cycle by different procedures was investigated. MMuLV production was inhibited in glutamine- and isoleucine (Gln-Ile)-deprived G0/G1 cells. In contrast, butyric acid treatment, which efficiently arrested the cells at the G0/G1 phase of the cell cycle, did not inhibit MMuLV production. Furthermore, the inhibition of MMuLV production caused by either Gln-Ile deprivation or by interferon (IFN) treatment was overcome by butyric acid treatment. Thus, the replication of MMuLV could be dissociated from cell proliferation. The inhibition of MMuLV production in Gln-Ile-deprived cell cultures was compared to the inhibitory effect of IFN, which is known to affect budding and release of the virus. Rates of MMuLV protein synthesis were not affected in both the IFN-treated and Gln-Ile-deprived cells. However, processing of the viral polyprotein Pre65gag into p30 was blocked in the Gln-Ile-deprived cells. Furthermore, whereas in IFN-treated cells, MMuLV accumulated on the cell surface and could be released upon treatment with trypsin, in Gln-Ile-deprived cells, no virions were released by such treatment. These results indicate that in cells arrested by Gln-Ile deprivation, MMuLV is inhibited at a posttranslation step. This step appears to precede the anti-MMuLV block induced by IFN.

Cytolytic activity of interferon-gamma and its synergism with 5-fluorouracil

Highly purified natural or recombinant human immune interferon (IFN-gamma) was found to be directly cytolytic to certain tumor cell lines in vitro. Out of 5 human tumor cell lines and one normal fibroblast line tested, the colon adenocarcinoma line HT-29 and the rhabdomyosarcoma line A673 were highly sensitive to cytolysis by interferon, as determined by 125I-iododeoxyuridine release in a 72 h microcytotoxicity assay. Cytolysis was marked at IFN-gamma concentrations of less than I U/ml, and it reached a near-maximal level at 6.4 U/ml. A synergistic cytolysis on HT-29 cells of IFN-gamma and 5-fluorouracil (5-FU) was observed at 5-FU concentrations ranging from 64 to 640 micrograms/ml. In contrast, no synergism was observed between IFN-gamma and mitomycin C. The direct cytolytic activity and synergistic cytolysis with 5-FU of the IFN-gamma preparations used in the present study were abolished completely by treatment with a neutralizing monoclonal antibody specific for human IFN-gamma.

Differential effect of interferon on glycoprotein and membrane protein of vesicular stomatitis virus released from murine and simian cells

Previous studies by Maheshwari et al. have indicated that vesicular stomatitis virus (VSV) released from interferon (IFN)-treated mouse L-929 (L) cells was structurally defective. Such virions had significantly smaller amounts of glycoprotein (G) and membrane protein (M). Olden et al. recently reported, however, that they were not able to repeat the findings of Maheshwari et al. We have examined the effect of IFN on VSV released from three different cell lines and observed that treatment of L-cells and secondary mouse embryo (ME) cells with an amount of mouse IFN that reduced infectious virus yield 100-fold, led to the release of VSV with reduced amounts of G and M proteins. However, at concentrations of IFN less than this concentration, this effect was not observed. In contrast, VSV released from human (Hu)IFN-treated primate BSC-1, cells showed no reduction in their G and M protein even at concentrations resulting in 400-fold decreases in infectious virus yield.

Effect of bovine recombinant alpha-1 interferon on inflammatory responses of bovine phagocytes

Bovine phagocytic cells (polymorphonuclear granulocytes, blood monocytes and alveolar macrophages) were treated in vitro with homogeneous, recombinant DNA produced bovine alpha-1 interferon (IFN-alpha 1). The effects seen comprised of enhanced bacterial uptake by all three cell types and increased Fc receptor activity in alveolar macrophages, inhibition of both directed and random migration of monocytes and polymorphs, increased enzyme release or inactivation, increased hydrogen peroxide generation, and decreased superoxide anion release by alveolar macrophages and polymorphonuclear leukocytes. These effects were dose- and time-dependent, the kinetics varying for the different cell types.

Interferon treatment inhibits pinocytosis

Treating mouse L cells with crude or purified mouse interferon inhibited fluid-phase pinocytosis. Inhibition was maximum at 24 h after treatment with 1,000 U of interferon per ml and was dose dependent and reversible with time. Pinocytosis was inhibited when human and chicken embryo cells were treated with homologous, but not heterologous, interferons.

Interferon treatment inhibits pinocytosis

Treating mouse L cells with crude or purified mouse interferon inhibited fluid-phase pinocytosis. Inhibition was maximum at 24 h after treatment with 1,000 U of interferon per ml and was dose dependent and reversible with time. Pinocytosis was inhibited when human and chicken embryo cells were treated with homologous, but not heterologous, interferons.

Tunicamycin enhances the antiviral and anticellular activity of interferon

The inhibitory effects of interferon on virus multiplication and cell growth are significantly enhanced by treatment with tunicamycin. Potentiation of antiviral activity was found only with enveloped viruses and not with nonbudding viruses. Changes in the plasma membrane of treated cells may account for this effect, since enveloped viruses bud from the cell surface as a terminal step.

Reversible increase in the saturation of C18 fatty acids induced by diphtheria toxin in tissue culture cells

Diptheria toxin (DT) reversibly increases the saturation of the long-chain C18 fatty acids (C18FA) in concentrations which are at least 100-fold smaller than the concentrations which completely inhibit host cell protein synthesis. The concentrations required for induction of the increase in the saturation of the C18FA in fibroblasts are 100-fold smaller than the concentrations for the epithelial cells. The increase in saturation of the C18FA was proportional to the concentration of DT. A cytopathic effect appeared with DT concentrations which induced a near-maximal increase in the saturation of the C18FA, but the cells remained viable. However, at very high concentrations of DT and depending on the type of cell, there was no change in the fatty acids, and the treated cells disintegrated. Interferon, which also induces a reversible increase in the saturation of the C18FA (K. Apostolov and W. Barker, FEBS Lett. 126:261-264, 1981), produces a cumulative effect when used in conjunction with DT. This additive effect of DT and interferon is discussed in the light of other similar biological activities of these agents.

Fatty acid desaturation-promoting factor (DPF) induced by interferon

Interferon (IFN) induces changes in the saturation of the long-chain 18 carbon fatty acids (C 18 fatty acids). After pulse treatment of human and bovine cells with HuIFN-α and with HuIFN-β there was a drastic but reversible increase in the saturation of the C 18 fatty acids (Apostolov & Barker 1981).

Direct cytolysis by partially-purified preparations of immune interferon

Mouse IFN gamma preparations purified 30-fold were found to have direct cytolytic activity against a number of tumor and normal cells. Cell killing was determined using a sensitive, rapid and accurate assay which employed very low numbers of cells and very small quantities of interferon. The cytolytic activity of IFN gamma on 11 murine tumor cell lines was investigated. A 20-fold difference was found between the most-sensitive cell type, P-388 lymphoma, versus the most resistant cell type, C127v leukemia. A number of normal mouse cells was also found to have low to intermediate sensitivity to the cytolytic action of IFN gamma. Human IFN gamma was also shown to have cytolytic activity which, like mouse IFN gamma, was relatively species-specific. Direct cytolysis was not found to be a characteristic of IFN-alpha/beta. Different mechanisms of action for the antiviral and cytolytic activities of IFN gamma are indicated because the cytolytic titer of IFN gamma did not parallel its antiviral titer on most cell types and increasing the cell number produced a decrease in the cytolytic titer and an increase in the anti-viral titer. High concentrations of IFN gamma (i.e., 2,900 units/ml) resulted in complete lysis of cells within 24 h, while lower concentrations (i.e., 700 units/ml) resulted in a reversible inhibition of cell growth during this time period. Evidence that the cytolytic substance in the IFN gamma preparation was IFN gamma include the following: (1) both antiviral and anticellular activities copurified through a 30-fold purification; and both activities were (2) relatively species-specific; (3) sensitive to heat; (4) inactivated by low pH and (5) neutralized by antibodies to IFN gamma. Therefore, we propose the possibility that direct cytolysis is yet another of IFN gamma's distinctive antivities.

Quantitative analysis of intramembrane particle (IMP) distribution on biomembranes after freeze-fracture preparation by a computer-based technique

An improved method for the quantitative analysis of intramembrane particles (IMPs) on freeze-fracture faces of biomembranes is described. The analysis provides, first, the number of IMPs per 1 micrometer2, second, the coefficient of dispersion (CD) of unweighted and weighted (i.e. the finite size is taken into consideration) IMP distribution, and, third, the diameters of IMPs. Additional data for further statistical evaluation are also derived. These data make it possible to numerically describe and characterize fracture faces of a membrane in a defined physiological state. They allow for comparison of normal membranes with experimentally induced alterations of the same specimen in other experiments, and for observation of differences between normal and malignant cells. Furthermore, such an analysis provides the basis for a dynamic interpretation of biomembrane components seen on the static freeze-fracture micrographs. With this numerical analysis, descriptive terms for IMP distribution such as 'random', 'aggregated' or 'clustered', which cannot be evaluated or verified, are avoided. The method, based on the Poisson statistic which provides a means for the description of different particle density distributions, is described. The validity of the method is demonstrated on artificially generated pictures and by an analysis of erythrocyte membranes before and after spectrin depletion.

Interferon inhibits Sendai virus-induced cell fusion: an effect on cell membrane fluidity

Interferon can affect several cellular functions, in addition to its antiviral activity. We report here that pretreatment of human cells with homologous interferon significantly inhibits cell fusion induced by Sendai virus and that this refractory state is accompanied by a decrease in cell plasma membrane fluidity. Multinucleate cell formation induced by beta-propiolactone-inactivated Sendai virus in human fibroblast cells (a system in which fusion results from an interaction of the viral glycoprotein with the cell membrane) was inhibited by more than 90% after addition of human interferon for 18-24 hr. This inhibition could be neutralized by antiserum to interferon. Furthermore, inhibitor studies with cycloheximide and actinomycin D clearly indicated that synthesis of protein and RNA is necessary to establish the resistant state. To determine whether the inhibition of Sendai virus-induced cell fusion resulted from interferon-induced changes at the cell plasma membrane, experiments were carried out using the fluorescence probe 1,6-diphenyl-1,3,5-hexatriene, which is capable of sensing molecular motions in the hydrocarbon core of the bilayer structure. A significant decrease in the membrane fluidity of interferon-treated cells was observed. It is likely, therefore, that the inhibitory effect on Sendai virus-induced cell fusion observed in interferon-treated cells results from an increased rigidity of the target cell membrane.

Interferon-mediated inhibition of adenylate cyclase in mouse cells

Adenylate cyclase activity was measured in mouse cell plasma membrane after 30 units/ml of interferon (IFN) treatment. The basal and Gpp(NH)p stimulated enzyme activity in LB cell was inhibited by 20%-40% throughout the time course of treatment (30 min to 18 h). The reduced enzyme activity was not associated with enhanced breakdown of cAMP, but was related to alteration in the catalytic component of the enzyme. Moreover, there was no change in the affinity for guanine-nucleotide regulatory unit and 1 X 10(-7) M Gpp(NH)p was required to obtain half-maximal activation with either type of membrane. Interferon action on adenylate cyclase was biphasic, at 10 u/ml it was stimulatory and between 30 and 1000 u/ml it inhibited the enzyme activity to a great extent; but IFN did not exert its effect directly on the enzyme. The reduction in enzyme activity was comparable to a reduction in the intracellular level of cAMP in most of the interferon-sensitive cell lines studied. We propose, therefore, that the inhibitory effect on adenylate cyclase is related to a step in the development of antiviral activity.

Effect of interferon on phospholipid methylation by peripheral blood mononuclear cells

The effect of human interferon (IFN) preparations on the metabolic pathway leading to the synthesis of phosphatidylcholine (PC) by a stepwise addition of methyl groups to phosphatidylethanolamine (PE) was investigated in human peripheral blood mononuclear (PBMN) cells. An inhibition of the synthesis of PC via this pathway was regularly observed with both alpha- (recombinant or natural) and beta-IFN. This inhibition was apparent within the first 5 min of treatment, reached its maximum between 15 min and 1 hr, and persisted at the same level until 6 hr, the last time point examined. Each of the transmethylated products of PE underwent a similar inhibition, as measured by the turnover rate of individual products. The intracellular pool of the methyl donors, methionine and S-adenosyl-methionine (SAM), was shown to be unaffected. The methyltransferase activity of IFN-pretreated cell extracts was unchanged. These findings support the hypothesis that IFN induces a functional change in phospholipid methylation at the level of organized membrane-bound phospholipid methyltransferase enzymes in intact cells.

Antiretroviral effect of interferon: proposed mechanism

Interferon (IFN) treatment of NIH Swiss mouse embryo cells chronically infected with Rauscher murine leukemia virus (R-MuLV) drastically reduced the release of virus particles from the cells. The characterization of intracellular and extracellular viral specific proteins and polyproteins immunologically with various antisera, and structurally by tryptic digest mapping experiments, indicated that the antiretroviral action of IFN was not due to an IFN-induced alteration in the synthesis of any viral protein. Steady state labeling experiments, however, showed that the processing of three viral specific precursor polyproteins, namely gPr90env, Pr40gag, and Pr25gag, were perceptively slowed in IFN-treated cells. This effect was apparently not related to the ability of these proteins to be modified by phosphorylation or glycosylation after translation since these processes occurred normally in the IFN-treated cells. The treatment of cells with IFN also caused the accumulation of a small amount of a fucosylated viral glycoprotein precursor, termed gP93env, in virus. With the exception of this minor protein, virus released from IFN-treated cells were normal in their content of viral proteins. These virus particles were only slightly less infectious, particle for particle, than virus released from control cultures. Based on these results, we suggest that IFN causes an as yet unelucidated alteration in cell membrane structure of function, or both, which prevents either the insertion of viral core precursor molecules into membrane or the recruitment or clustering of such viral polyproteins into virus assembly centers in the membrane. This suggested mechanism of IFN action is discussed in detail.

Interferon induces an antiviral state in ganglioside-deficient transformed mouse fibroblasts

The antiviral activity of mouse fibroblast interferon against vesicular stomatitis virus was investigated in L-929 mouse fibroblasts and the ganglioside-deficient L-929 mutant cells (ATCC clone NCTC 2071). Although it has been widely reported that gangliosides serve as primary receptors for interferon at the cellular membrane, only a small difference in interferon sensitivity was observed between the wild-type L-929 and the ganglioside-deficient NCTC 2071 cells. It was not possible, however, to overcome this difference by administration of exogenous gangliosides.

Interferon-resistant cell line lacks fatty acid cyclooxygenase activity

A clone of L1210 mouse leukemia cells selected for resistance to both the antiviral and anticellular properties of mouse interferon were essentially devoid of fatty acid cyclooxygenase activity. Experiments in which broken cell preparations were mixed or the two cell types were cultivated together failed to indicate the presence of a diffusible enzyme inhibitor. Fatty acid lipoxygenase activity of similar magnitude was detectable in both cell types. A selective impairment of fatty acid cyclooxygenase in interferon-resistant cells is consistent with recently described data suggesting that this enzyme may play a crucial role in mediating the antiviral and anticellular effects of interferon.

Interferon inhibits the redistribution of cell surface components

Interferon treatment impairs the ability of cells to redistribute cell surface receptors for concanavalin A (Con A). The effect of interferon becomes evident within 3-6 h and is maximal within 36-48 h. Highly purified human fibroblast interferon (> 2 x 10(8) U/mg of protein sp act; concentration; 640 U/ml) caused approximately 85% inhibition of capping of fluorescein-conjugated Con A in interferon-sensitive HeLa-S3 cells at 36 h from the beginning of treatment.

Interferon inhibits the conversion of 3T3-L1 mouse fibroblasts into adipocytes

Confluent Swiss mouse 3T3-L1 fibroblasts slowly differentiate functionally and morphologically into adipocytes, a conversion hastened by insulin. The cells are sensitive (although less than L929 cells) to the antiviral action of mouse fibroblast interferons but not to interferons from heterologous species (human and chicken). Cultures stimulated with insulin in the presence of partially purified or electrophoretically pure mouse interferons have a much lower percentage of cells accumulating lipid than do insulin-treated control cultures. Interferon-treated cell cultures also contain much less triglyceride, cholesterol, and cholesterol esters than do replicate control cultures stimulated by insulin to differentiate. Increased de novo lipid biosynthesis that occurs during differentiation is inhibited, as determined by incorporation of [14C]acetate into lipids extractable by the Folch method. This incorporation is a sensitive bioassay of the antidifferentiation effect of interferon; less than 1 antiviral unit is inhibitory. Variously inactivated or mock interferon preparations as well as interferons from several heterologous species fail to inhibit 3T3-L1 adipocyte conversion. Interferon is inhibitory even when applied as long as 3 days after insulin stimulation. The effect of interferon does not appear to depend upon its competition with insulin for cell surface receptors. Because interferon can alter the program of events involved in conversion of 3T3-L1 fibroblasts into adipose cells, it may be able to affect the regulation of eukaryotic cell differentiation.

The complete purification of human leucocyte interferon

Human leucocyte interferon (HuLeIF) has now for the first time been purified by a series of techniques involving precipitation, gel filtration, and affinity chromatography with Cu-chelate, blue dextran, and antibody. The two major species of HuLeIF were identified as two clearly separable and stainable proteins representing 85% of the biological activity with molecular weights of 18,400 and 20,180 daltons. Three more subspecies of HuLeIF were demonstrated with molecular weights of 19,500, 20,900 and 22,130 daltons, representing 15% of the biological activity. Specific activity of pure interferon is 2 x 10(9) interferon units/mg protein. Recovery was about 50%, and the purification factor exceeded 350,000.

Interferon-treated cells release vesicular stomatitis virus particles lacking glycoprotein spikes: correlation with biochemical data

Earlier we reported a reduction to 1/30th-1/100th of the original number of infectious particles in the infectious vesicular stomatitis virus (VSV) released from L cells treated with 10 or 30 reference units of interferon per ml. However, in these cultures virus particle production, as measured by VSV particle-associated viral RNA, virus nucleocapsid protein, and viral transcriptase, was inhibited by less than 10%. Data reported in this paper show that there was a significant reduction in glycoprotein and membrane protein of VSV particles released from interferon-treated cells. Evidence supporting the deficiency of glycoprotein in VSV released from interferon-treated cells was derived from electron microscopic studies. Under conditions where glycoprotein spikes or projections were clearly detectable on the surface of VSV released from cells not treated with interferon, very few spikes were observed on VSV released from interferon-treated cells. These results suggested that interferon-treated cells produced VSV particles with low infectivity and that this low infectivity may be related to the reduced amount of glycoprotein and membrane protein incorporated into such particles.

Enhancement of cellular protein synthesis sensitivity to diphtheria toxin by interferon

In attempts to determine whether, by analogy to cholera and tetanus toxins, diphtheria toxin (DT) can also relieve the antiviral effect of interferon (IF), we found that it rather enhanced the inhibitory effect of IF on the replication of murine leukemia virus in chronically infected NIH/3T3 cells. This enhancement was found to be a consequence of an increased sensitivity to DT of cellular protein synthesis in IF-treated cells. IF stimulated the anti-protein synthesis activity of DT in both mouse cells that are known to be highly resistant to this toxin and in human HeLa cells that are highly sensitive to this toxin. This stimulation was dependent on IF dose. The effect of IF on DT action was strictly species specific, indicating that it was not a consequence of the mere binding of IF to the cell membrane, but rather reflected the cellular changes that followed this initial binding. IF was found to be capable of potentiating intact DT, but could not potentiate its fragments in any combination. IF did not have any effect on the in vitro nicotinamide adenine dinucleotide glycohydrolase activity of DT, suggesting that the effect of IF is not due to molecular modification of the toxin.

Selective inhibition of glycoprotein and membrane protein of vesicular stomatitis virus from interferon-treated cells

A 200-fold inhibition in the titer of infectious vesicular stomatitis virus (VSV) was produced in cultures of Ly cells treated with 30 reference units of interferon per milliliter. Virus particle production, as measured by VSV particle-associated transcriptase, or nucleocapsid protein was inhibited by a maximum of tenfold. The glycoprotein and membrane protein content was reduced in VSV derived from interferon-treated cells. Thus interferon-treated cells may have produced VSV particles with low infectivity, which may be related to the reduced amount of glycoprotein incorporated into such particles. These findings resemble those reported in interferon-treated cells infected with murine leukemia viruses.

Electrophoretically pure mouse interferon exerts multiple biologic effects

Electrophoretically pure mouse interferon was examined for a number of biologic effects previously ascribed to crude or partially purified interferon preparations. These effects include: inhibition of the growth of a transplantable tumor in mice; inhibition of cell multiplication of mouse tumor cells in vitro; enhancement of the expression of histocompatibility antigens on mouse tumor cells in vitro; inhibition of antibody formation in vitro; inhibition of sensitization to sheep erythrocytes and the expression of delayed type hypersensitivity in mice; enhancement of natural killer cell activity in vivo and in vitro; enhancement of cell sensitivity to the toxicity of poly(I)-poly(C); and enhanced production ("priming") of interferon production in vitro. Our results establish that the molecules responsible for the antiviral action of interferon are also responsible for these varied biologic effects.

Effect of sodium butyrate on the antiviral and anticellular action of interferon in normal and MSV-transformed cells

Sodium butyrate enhances the antiviral and anticellular action of interferon in MSV-transformed cells but has no such effect in normal cells. The increased sensitivity could be mediated at least partially by the butyrate-induced elaboration of the microtubule and microfilament network.

Effect of interferon on concentrations of cyclic nucleotides in cultured cells

Constant intracellular concentrations of both adenosine 3',5'-cyclic-monophosphate (cyclic AMP) and guanosine 3',5'-cyclic-monophosphate (cyclic GMP) were obtained when leukemia L1210 cells were cultivated under steady-state conditions in the chemostat. In this sensitive and controlled system addition of mouse interferon resulted in a rapid (5-10 min) increase in the intracellular concentration of cyclic GMP, which preceded by several hours an increase in the intracellular concentration of cyclic AMP. In contrast to the effect of interferon, addition of prostaglandin E1 induced a rapid increase in the intracellular concentration of cyclic AMP without markedly affecting the intracellular concentration of cyclic GMP. It is suggested that the rapid effect of interferon on cyclic GMP plays a role in mediating some of the effects of interferon on cells.

Delay in growth and the development of nephritis in rats treated with interferon preparations in the neonatal period

Suckling rats were injected for 14 to 17 days with potent rat-cell-culture interferon preparations or various heterologous interferon or control preparations. Only treatment with rat interferon resulted in a delay in growth and maturation of different organs and the subsequent development of an "immune complex" type nephritis. Thus, 38 of 43 rats treated with rat interferon developed a severe glomerulonephritis. Thus, 38 of 43 rats treated with rat interferon developed a severe glomerulonephritis, whereas only 3 of 99 rats in the various control groups had minimal renal lesions. Deposits of IgG and C3 along the glomerular basement membrane were only seen in interferon-treated rats.