Inhibitory effects of interferon-gamma on the T suppressor cell circuit in contact sensitivity

Interferon-gamma: a historical perspective

This article reviews the main lines of thinking and exploration that have led to our current conception of the role of IFN-gamma in immune defense and autoimmunity. In 1965 the first report appeared describing production of an interferon-like virus inhibitor in cultured human leukocytes following exposure to the mitogen phytohemagglutinin. In the early 1970s the active principle became recognized as being distinct from classical virus-induced interferons, leading to its designation as immune interferon or Type II interferon, and eventually IFN-gamma. Up to that point interest in the factor had come almost exclusively from virologists, in particular those among them who were believers in interferon. Evidence first coming forward in the 1980s that IFN-gamma is indistinguishable from macrophage-activating factor (MAF), then a prototype lymphokine, was the signal for immunologists at large to become interested. Today IFN-gamma ranks among the most important endogenous regulators of immune responses.

Interferon-gamma in autoimmunity

Autoimmune disorders are characterized by abrogation of self-tolerance, resulting in emergence of activated self-reactive lymphocyte clones that trigger or maintain inflammatory reactions in specific organs. Interferon-gamma (IFN-gamma), as well as other cytokines, plays an important role as a regulator of the activation of self-reactive lymphocytes and of bystander and accessory cells that are involved in the autoimmune inflammatory response. In experimental models of autoimmunity, endogenous IFN-gamma has invariably been found to profoundly affect the disease course. However, it acts in one way in some diseases and in the opposite way in others.

Ultraviolet-induced suppressor T cells and factor(s) in murine contact photosensitivity. III. Mode of action of T-cell-suppressor factor(s) and interaction with cytokines

The mode of action of T-cell-suppressor factor (TsF) induced by ultraviolet B (UVB) preirradiation in terms of interaction with several cytokines was studied. Suppression of murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) by preirradiation of the sensitizing site to low doses of UVB was caused by antigen-specific suppressor T cells (Ts) and was not associated with the generation of efferent limb-acting suppressor cells. TsF released by Ts inhibited the proliferation of immune lymph node (LN) cells in vitro and reduced interleukin (IL)-2 production of these cells in an antigen-specific fashion without affecting the IL-2 receptor (IL-2R) expression. Both rIL-2 and rGM-CSF have the ability to restore CPS responses in the UVB-preirradiated mice when administered after but not before photosensitization. However, rIL-2 but not rGM-CSF counteracted the in vivo inhibitory effect of TsF. rGM-CSF did not affect the density of I-A+ epidermal Langerhans cells (LCs). It was suggested that TsF inhibited IL-2-mediated immune T-cell proliferation, while rGM-CSF reconstituted the CPS by enhancing the function of photodamaged LCs. These results indicate multiple steps of the UVB-induced immunosuppression circuit, each of which seems to be controlled by different immunomodulators.

Multiple sclerosis: an overview

Demyelinating lesions of MS are infiltrated by activated T-lymphocytes and macrophages with secretion of soluble factors. This results in the synthesis of oligoclonal immunoglobulin (IgG) by plasma cells. The activated T-lymphocytes migrate from the peripheral blood to the CNS. This hyperactive state is linked to a selective loss of the suppressor/inducer T-cell subset. Administration of a soluble factor--interferon gamma--enhances the immune response by promoting class II antigen expression on macrophages or astrocytes, resulting in a relapse. However, the reason for T-cell activation in peripheral blood is not known, nor is the antigen. Myelin basic protein (MBP) has been considered to be the target since MBP is able to induce chronic relapsing allergic encephalomyelitis (CRAE) in an animal model of MS. Yet other myelin antigens have succeeded in inducing CRAE in animal models, and anti-MBP antibodies have been found in healthy individuals. The possibility that the hyperimmune state results from a viral infection has not yet been proven. It is known that in Caucasians, a genetic susceptibility factor is linked to class II MHC. Using MRI it has been found that the presence of new plaques was not regularly correlated with relapses, which indicates that MS is an ongoing pathology process. Most drugs used in MS influence the immune response but have potential toxicity. Monoclonal antibodies offer the opportunity of specific targeting of T-cells and are promising for the future.

IL-2 influences the balance between immunity and unresponsiveness in the picryl (TNP) contact sensitivity system by blocking the development or action of an Lyt-2+, I-J+ T suppressor cell

Mice injected with antigen (picrylated spleen cells) intravenously fail to develop contact sensitivity. However, contact sensitivity occurs if these mice are injected with IL-2. This effect of IL-2 was reproduced in vitro by taking spleen cells 2 days after injecting antigen intravenously and culturing them with either 150 u/ml recombinant IL-2 for 2 days or by pulsing with 600-1200 u/ml IL-2 at 4 degrees C for 1 hr. After 2 days in culture these antigen-exposed cells transfer contact sensitivity to naive recipients in a 24-hr experiment. However, the ability of antigen-exposed cells, pulsed with IL-2, to transfer contact sensitivity is abolished when they are incubated with unpulsed antigen-exposed cells and as few as 1/16 of their number have a significant effect. This phenomenon is specific, as normal cell or cells from mice injected with oxazolonated cells intravenously have no effect. The suppressor cells were Thy-1+, Lyt-1-, 2+, I-J+ T cells. It was concluded that IL-2 prevents the development/action of antigen-specific T suppressor cells.

Multiple sclerosis: involvement of interferons in lesion pathogenesis

To investigate a possible role of interferons (IFNs) in lesion pathogenesis, central nervous system tissue from multiple sclerosis patients and control subjects was stained by immunocytochemical techniques in combination with monoclonal antibodies or polyclonal antisera for the demonstration of IFN-alpha, IFN-beta, and IFN-gamma. The results were correlated to lesion activity, to the presence of class I and class II major histocompatibility antigen-positive astrocytes, and to the composition of cellular infiltrates. IFNs were detectable in active but not in inactive chronic multiple sclerosis lesions. In acute multiple sclerosis plaques, all three types of IFN were widely distributed on glial elements and infiltrating cells. In active chronic multiple sclerosis, labeling of cells for IFN-alpha, IFN-beta, and IFN-gamma was most pronounced at the lesion edge and displayed distinct distribution patterns. Overall, IFN-gamma was more common than IFN-alpha and IFN-beta and was predominantly found on astrocytes. IFN-alpha was detectable mainly on macrophages. Distribution of IFN-beta partially overlapped with that of IFN-gamma and IFN-alpha, in that it was present on some astrocytes and on some macrophages. IFNs were rare in normal white matter remote from lesions and in the gliotic lesion center. Ia antigen and human leukocyte antigen ABC on astrocytes were distributed similarly to IFN-gamma and IFN-beta, respectively. These findings indicate that IFN-gamma may play a role in active lesion growth in multiple sclerosis, whereas IFN-alpha and IFN-beta may exert some local immunosuppressive effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon-gamma and Ia antigen are present on astrocytes in active chronic multiple sclerosis lesions

Using immunocytochemical techniques, presence of interferon (IFN)-gamma, IFN-alpha and Class II major histocompatibility (MHC) antigen (HLA-DR, Ia) was evaluated in active central nervous system (CNS) lesions of 11 patients with chronic multiple sclerosis (MS) and the findings were correlated with a detailed analysis of inflammatory cells. Both IFN-gamma and Ia antigen were detectable on astrocytes at the edge of active chronic MS lesions and in the adjacent normal-appearing white matter, where CD4+ (helper/inducer) T cells and interleukin-2 receptor (IL-2R)-positive cells were also found. IFN-alpha was predominantly seen on Ia-positive macrophages and not on astrocytes. Astroglia in the inactive lesion center and in normal CNS parenchyma were unreactive for both types of IFN and Ia antigen. These findings suggested that similar to the situation in vitro, IFN-gamma can also induce Ia-expression on astrocytes in vivo. Via local antigen presentation, IFN-gamma might thus play an important role in the development of MS lesions, while IFN-alpha might be involved in local immunosuppression.