Human leucocyte interferon: analysis of effect on MLC and effector cell generation

A new IFN-like cytokine, limitin, modulates the immune response without influencing thymocyte development

A novel IFN-like molecule, limitin, was recently identified and revealed to suppress B lymphopoiesis through the IFN-alphabeta receptor, although it lacked growth suppression on myeloid and erythroid progenitors. Here we have studied diverse effects of limitin on T lymphocytes and compared limitin with previously known IFNs. Like IFN-alpha and -beta, limitin modified immunity in the following responses. It suppressed mitogen- and Ag-induced T cell proliferation through inhibiting the responsiveness to exogenous IL-2 rather than suppressing the production of IL-2. In contrast, limitin enhanced cytotoxic T lymphocyte activity associated with the perforin-granzyme pathway. To evaluate the effect of limitin in vivo, a lethal graft-versus-host disease assay was established. Limitin-treatment of host mice resulted in the enhancement of graft-versus-host disease. Limitin did not influence thymocyte development either in fetal thymus organ cultures or in newborn mice injected with limitin-Ig, suggesting that limitin is distinguishable from IFN-alpha and -beta. From these findings, it can be speculated that the human homolog of limitin may be applicable for clinical usage because of its IFN-like activities with low adverse effects on, for example, T lymphopoiesis, erythropoiesis, and myelopoiesis.

Human nonspecific suppressive lymphokines

Since the term "lymphokine" first appeared in print over 20 years ago, a tremendous number of these soluble mediators of the immune system have been described. Within the past few years, many human nonspecific suppressive lymphokines have been identified. This review discusses the historical basis of immunologic suppression and suppressor factors. Later reports describing suppressive human lymphokines are then grouped into four categories: primarily stimulatory lymphokines that also mediate certain suppressive activities, suppressive lymphokines produced during altered states of immunity, suppressive lymphokines produced by exogenously stimulated lymphocytes, and suppressive lymphokines produced by unstimulated lymphocytes. Recent work I have been involved in focusing on the human suppressive lymphokine soluble suppressor factor (SSF) is also discussed.

Modulation of some Peyer's patch leukocyte functions following in vitro exposure to recombinant bovine alpha- and gamma-interferon

The immunomodulatory effects of recombinant bovine interferon-alpha 1(1) (rBoIFN-alpha 1(1] and -gamma (rBoIFN-gamma) on the response of bovine Peyer's patch leukocytes (PPL) to in vitro mitogenic stimulation were studied. The proliferative response of PPL to concanavalin A (Con A) and pokeweed mitogen (PWM) was significantly inhibited by the addition of 5-1000 units/ml of rBoIFN-alpha 1(1). In contrast, rBoIFN-gamma showed significant enhancement of 3H-Thymidine (3HTdR) incorporation of PPL cultures at concentrations of 5-500 units/ml. Although the results of this study substantiated the previously reported suppressive ability of IFN-alpha 1(1) and the stimulating capacity of IFN-gamma, suppression or enhancement of lymphocyte proliferation was shown to be dependent on the concentration of the polyclonal activator and the length of time the target cells were exposed to IFN. Pre-exposure of target cells to rBoIFN-alpha 1(1) significantly increased its suppressive activity against the PPL response to Con A stimulation. In contrast, pre-exposure of PPL to rBoIFN-gamma did not affect its stimulatory capacity. Prestimulation of target cells with Con A significantly decreased the stimulatory capacity of rBoIFN-gamma and the suppressive activity of rBoIFN-alpha 1(1). These data demonstrate qualitative differences in the effects of rBoIFN-alpha 1(1) compared to those of rBoIFN-gamma on immune cells other than commonly studied circulating leukocytes.

The effect of IFN-gamma and alpha on Con-A stimulated T-cell proliferation: role of monocytes

Interferon gamma (IFN-gamma) and alpha (IFN-alpha) have been shown to influence T-cell proliferation in several systems. Since both species of IFN affect monocyte (Mo) functions, it is conceivable that these effects are mediated through Mo. In the present study, the effect of IFN-gamma and alpha on concanavalin A (Con A)-driven T-cell proliferation was investigated under suboptimal culture conditions. T-cell proliferation was augmented by IFN-gamma. The stimulatory effect of IFN-gamma was Mo mediated and required the pretreatment of Mo with IFN-gamma prior to co-culture with T-cells. Addition of IFN-gamma during co-culture or pretreatment of T-cells with IFN-gamma was ineffective in achieving augmentation. IFN-gamma induced enhanced T-cell proliferation was not due to increased interleukin-I (IL-I) production by Mo pretreated with IFN-gamma, because addition of IL-I to control Mo-T-cells co-culture failed to increase T-cell proliferation. In contrast, IFN-alpha suppressed T-cell proliferation. The inhibitory effect of IFN-alpha was not mediated through Mo and could be achieved by preincubating the T-cells with IFN-alpha. These results demonstrate opposing effects of the two species of IFN on Con A-driven T-cell proliferation. In addition, Mo play an obligatory role in IFN-gamma induced stimulation, whereas Mo-IFN-alpha interaction is not required for IFN-alpha mediated suppression of T-cell proliferation.

Intestinal immunity and inflammation: recent progress

The previous sections illustrate that we are still defining (a) which sets of lymphoid cells are present in the intestine and which are not, (b) which sets are peculiar to the intestine, and (c) how the sets that are there function in the intestinal microenvironment. An understanding of the latter point is going to require knowledge of how these sets communicate with and regulate one another via cell surface molecules such as MHC class I and class II molecules, and via soluble mediators or lymphokines. The recent advances in various technologies make this a particularly exciting time in this field because the tools are now available to address and answer some of these basic and important questions in mucosal immunology. At the same time these advances hold great promise for our eventual understanding of chronic inflammatory diseases of the intestine. As was mentioned at the outset, the immune system has considerable power for both protection and destruction. It remains a puzzle how this latter potential is contained and controlled in the intestine of most individuals, such that they do not have inflammatory disease even in the setting of intense stimulation by substances, such as endotoxin, that are phlogistic elsewhere in the body. An answer to the question of why everyone does not have intestinal inflammation could provide new insights into the mechanisms involved in chronic intestinal inflammatory diseases. The recent advances just detailed, as well as others sure to come, suggest that it is only a matter of time before such questions are answered.

Similar effects of treatment with alpha interferon on the protein synthesis of human large granular lymphocytes, T cells, and monocytes

Preparations of human large granular lymphocytes (LGL), T cells, and monocytes (MC) were obtained through centrifugation on Percoll gradients and preparative E-rosetting. The different preparations contained more than 80% of the appropriate cell type, as judged by their ability to lyse 51Cr-labelled K562 cells, cell morphology, and the presence of cell surface structures recognized by the OKT3, OKT10, Leu 7 and OKM1 monoclonal antibodies. The protein synthesis is unstimulated and alpha interferon (IFN-alpha)-treated cells of the different types was studied by subjecting 35S-methionine-labelled cell extracts to two-dimensional gel electrophoresis. The general pattern of protein synthesis in LGL and T cells was virtually identical, whereas at least 7 major proteins were synthesized at a higher rate in monocytes. The effects of IFN-alpha on the protein synthesis of LGL and T cells were identical, IFN-alpha increasing the rate of synthesis of 9 proteins. These proteins were also expressed, but not always IFN-augmentable, in monocytes. No additional, cell-type associated, IFN-inducible proteins were found. This suggests that the augmenting effect of IFN-alpha on the cytotoxic capacity of LGL, T cells, and monocytes may be to affect common steps in their lytic machineries.

Selective effects of alpha interferon on human T-lymphocyte subsets during mixed lymphocyte cultures

Mixed lymphocyte reaction (MLR) cultures of human lymphocyte subsets with or without the addition of physiological doses of human alpha interferon (IFN-alpha) were compared with respect to surface marker phenotypes and proliferative capacities of the responder cells. A selective depression on the T4 (inducer) T-cell subset could be demonstrated as a sequence of events: decreased fluorescence intensity of the T4 inducer cells (day 2 of culture), decreased percentages of T4 cells as demonstrated by cell cytofluorometry (days 3-6 of culture), and decreased 3H-thymidine incorporation of purified T4 cells and decreased numbers of T4 cells harvested from IFN MLRs (days 5-6 of culture). In contrast, it was shown that the T8 (cytotoxic/suppressor) subset in MLRs was either not affected or slightly stimulated by the addition of IFN. The depression of the T4 cells by IFN was accompanied by a decrease in the number of activated T cells expressing Ia antigens. On the other hand, IFN MLRs contained greater numbers of cells expressing the T10 differentiation antigen. In experiments with purified T-cell subsets the IFN effect was exerted directly on the T4 cells and not mediated by either T8 suppressor cells or monocytes. These findings are discussed in relation to other immunoregulatory effects of IFN-alpha.

Effect of interferon on cell proliferation and generation of cytotoxic potential in mixed autologous and allogeneic lymphocyte cultures

Autologous and allogeneic mixed lymphocyte cultures (AMC and MLC) were assayed for blastogenesis, generation of cytotoxic potential, and the effect of interferon (IFN-alpha) on these features. The cells of the mixed cultures lysed K562, Daudi, and autologous and allogeneic phytohaemagglutinin blasts. Stimulator-specific cytotoxicity was observed only in MLC. B blasts induced with Staphylococcus aureus were only affected in a stimulator-specific manner. Short-term IFN treatment of the MLC-derived effectors before the lytic assay enhanced the nonspecific component of cytotoxicity. Cell proliferation was considerably lower in AMC than in MLC. This was decreased when IFN-alpha was added at the initiation of the cultures. The presence of IFN influenced the generation of lytic potential. Comparison of the lysis of the different targets exerted by MLC-activated cells suggested that the specific component was more substantially elevated than the nonspecific one. It is likely that the IFN induced such modifications in the culture conditions that favoured the proliferation of the specific clone. Re-exposure of lymphocytes cultured in the presence of IFN to another dose of IFN before the assay had no influence on their lytic potential.

13 native human interferon-alpha species assessed for immunoregulatory properties

Human leukocytes treated with Sendai virus yield interferon predominantly of the alpha-type (HuIFN-alpha). Successful attempts to purify these "native" species have been performed and the final analysis, which included an SDS-PAGE disclosed 13 stained and separated IFN-proteins in the molecular weight-range of 16.6-23.5 kD. These stained IFN proteins were eluted individually from the gel slices and assessed for antiviral activity in human, monkey, and bovine cells, as well as for immunomodulatory effects (in vitro) on human lymphocytes. Based on equal amounts of (human) IFN units, as determined by IFN titration on human cells, the "immunological efficacies" of the 13 different HuIFN-alpha species were determined in three different immunological systems with the following results: (1) Augmentation of the NK function was a property of all species, although the two lower species (16.6 kD, 16.9 kD) were clearly less efficient with "titers" in the NK system reduced 25-fold. (2) Enhanced expression of HLA on lymphocyte membranes was induced by all the HuIFN-alpha species to the same extent. (3) Addition of IFN to mixed lymphocyte reaction (MLR) augmented the CML outcome of the cultures. In this system all 13 species exerted their effect equally well; no clear inferiority or superiority of individual species were seen. It is concluded that the fractionation of the IFN-alpha into 13 species does not give rise to IFN species which are specific only for some functions and not for others. All species exert all functions, although the relatively "immunological" titers in the NK system varied within the species.

Interferon inhibits the generation of allospecific suppressor T lymphocytes

The effect of human interferon alpha on the differentiation of functional populations of lymphocytes during the human allogeneic response in vitro was studied. Interferon alpha inhibited the generation of allospecific suppressor T lymphocytes that normally develop from lymphocytes primed in vitro against allogeneic cells. This effect was not the result of the destruction by interferon of precursor suppressor cells but rather to inhibition of their differentiation into active suppressor T lymphocytes. This inhibition was reversible and could be overcome by repeated allogeneic stimulation even in the presence of interferon. Inhibition of the generation of allospecific suppressor lymphocytes by interferon might play an important role in the allogeneic response. Interferon inhibited the proliferation of lymphocytes after allogeneic stimulation in a primary mixed lymphocyte reaction but enhanced their cytotoxicity. Despite the inhibitory effect in the primary mixed lymphocyte reaction, the specific secondary proliferative response of lymphocytes primed against a single HLA-DR antigen was only slightly affected by interferon. On the other hand, the nonspecific secondary proliferative response of lymphocytes primed in the presence of interferon was significantly reduced, indicating that interferon might decrease the recruitment of nonspecific "irrelevant" clones of responding cells during the sensitization period.

Effect of a homologous beta-interferon preparation on degradation of Escherichia coli and on lysosomal enzyme activities in mouse peritoneal macrophages

The degradation of 32P-labelled E. coli and the activity of three lysosomal enzymes, acid phosphatase, cathepsin D and beta-glucuronidase, in mouse peritoneal macrophages (MPM) were tested after cultivation of the cells for 24 or 48 hours with 10(1) - 10(4.7) U per ml of a homologous beta-interferon preparation (IFN-beta). Low to moderate concentrations of IFN-beta did not influence bacterial degradation in MPM. However, a reduction in bacterial degradation by 20 per cent or more was seen when the MPM were pre-treated with 10(4.7) U per ml for 24 hours or 10(3) U per ml of IFN-beta for 48 hours. Cultivation of the MPM with 10(2) U per ml of IFN-beta suppressed the activities of the lysosomal enzymes, provided that the cells were treated for 48 hours. The beta--glucuronidase activity was significantly reduced also after 24 hours. Increased release of beta-glucuronidase from MPM to the medium during cultivation with 10(2) U per ml of IFN-beta was also observed. Specific anti-IFN-beta globulin abolished the suppression by IFN-beta on the lysosomal enzyme activities. A human IFN-alpha preparation did not influence bacterial degradation or lysosomal enzyme activities in MPM.

HLA control of interferon production in the human mixed lymphocyte culture

This report describes studies of interferon production in the human mixed lymphocyte culture. Similar levels of interferon were detectable in two-way, unidirectional, and double-irradiated mixed lymphocyte culture combinations. Following an initial lag period of 1-2 days interferon production showed a peak response on days 3-4 and, in most combinations, was detectable through day 7 of the mixed lymphocyte culture. Interferon-gamma was the predominant type of interferon produced, along with a minor component of interferon activity detectable in some culture combinations which appeared similar to interferon-alpha. Interferon was not produced in HLA identical sibling combinations except for one brother-sister pair who were the donor and recipient of a kidney allograft. Interferon was produced in sibling and unrelated individual combinations that expressed HLA-A, HLA-B, or HLA-DR region incompatibility, with higher concentrations of interferon detectable in the HLA-DR region imcompatible combinations.

Interferon-induced augmentation of cytotoxic killer cell generation in mixed lymphocyte cultures: analysis of the effector cell product

Alloreactive cytotoxic lymphocytes were generated during mixed lymphocyte cultures (MLC). Human leucocyte interferon added during MLC gave rise to a moderate inhibition of thymidine uptake, yet augmentation of the allospecific cytotoxic product generated was found. Effector cell activities after MLC in the presence and absence of interferon against autologous cells were negligible, whereas NK-sensitive targets and antibody-coated target cells were killed to a higher extent, comparably, by cells generated during MLC in the absence of interferon. Cell separation experiments and cold target inhibition experiments were performed and showed that the effector cells generated with and without interferon had similar characteristics and were distributed among the same lymphocyte subpopulations. The key conclusion was that the augmented cytotoxicity was caused by alloreactive T cells, most of which were F(c) gamma receptor-negative, and was not due to enhanced 'NK-like' or antibody-dependent cell-mediated cytotoxic activity induced by interferon.

Human tumor-lymphocyte interaction in vitro. VII. Blastogenesis and generation of cytotoxicity against autologous tumor biopsy cells are inhibited by interferon

In a high proportion of cases blood lymphocytes from cancer patients cultured with autologous tumor biopsy cells undergo blastogenesis. In addition, cytotoxicity against autologous tumor cells is generated. These autoactivated lymphocytes also kill the highly NK-sensitive K-562 and Molt-4 cells. Addition of interferon (IF) at the initiation of the cultures inhibited blastogenesis and the generation of autologous cytotoxicity. On the other hand, lymphocytes already activated for autologous killing in the mixed cultures were not affected by short-term IF treatment prior to the cytotoxic assay. Lymphocytes cultured alone lose their cycotoxicity against K-562. However, when IF was present in these cultures the lymphocytes were cytotoxic for K-562. In addition, lymphocytes cultured for 6 days under conditions which did not result in activation killing of Molt-4 cells could be induced by short-term incubation of the effectors with IF.

A murine leukemia virus yield-reduction semi-microassay for interferon

Interferon (IF) treatment of murine cells chronically producing infectious leukemia virus results in a decreased yield of extracellular virus. We have utilized this principle to develop a useful semi-microassay for IF. The assay incorporates the desirable features of both virus yield-reduction and plaque-reduction assays, yet has few of the undesirable features associated with many IF assays. Being a semi-micro assay, it is amenable to the screening of multiple samples for IF and is economical with respect to cell culture materials, reagents and amount of sample required for testing.