The influence of interferon alpha and gamma, singly or in combination on human natural cell mediated cytotoxicity

Neutralizing interferon alpha as a therapeutic approach to autoimmune diseases

Therapeutic antibodies directed against tumor necrosis factor alpha (TNF-alpha) for the treatment of rheumatoid arthritis, and against the human EGF receptor-2 (HER2) receptor for the treatment of breast cancer have provided significant clinical benefit for the patients. The success of these antibodies has also provided strong support for the possibility that increased activity of cytokines or growth factors is causally implicated in a variety of human diseases. Interferon alpha (IFN-alpha) is induced by viruses (linked by epidemiological studies to autoimmune diseases), has significant direct effects on both epithelial cells and the immune system, and then can be further induced by the autoantibodies and apoptotic cells generated by the actions of IFN-alpha. The direct and deleterious impact on target tissues, the ability to induce an autoimmune response, and the potential for a self-sustaining cycle of induction and damage suggests that IFN-alpha could be a pivotal factor in the development of autoimmune diseases. This review will evaluate the rationale for, possible approaches to, and safety concerns associated with, targeting interferon alpha (IFN-alpha) as a therapeutic strategy for the treatment of autoimmune diseases. While the approach may be applicable to several autoimmune diseases, there will be an emphasis on systemic lupus erythematosus and insulin dependent diabetes mellitus.

Suppression of lymphokine-activated killer (LAK) cell induction mediated by interleukin-4 and transforming growth factor-beta 1: effect of addition of exogenous tumour necrosis factor-alpha and interferon-gamma, and measurement of their endogenous production

Recombinant human interleukin-4 (rhIL-4) and transforming growth factor-beta 1 (TGF-beta 1) suppressed the induction of lymphokine-activated killer (LAK) activity induced by recombinant human interleukin-2 (rhIL-2) in peripheral blood lymphocytes. DNA synthesis and the expression of the p55 alpha chain of the IL-2 receptor (Tac antigen) were also inhibited. The inhibitory effect was greatest when these factors were added during the first 48 h of a 4-day culture, with reduced cytolytic activity against both natural killer (NK) resistant and NK-sensitive tumour cell line targets. The suppressive action of both cytokines was accompanied by a reduction in tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) levels in lymphocyte culture supernatants. Recombinant human IFN-gamma (rhIFN-gamma), but not recombinant human TNF-alpha (rhTNF-alpha) was able to overcome the inhibitory effect of recombinant human interleukin-4 (rhIL-4) on LAK induction and DNA synthesis but not Tac antigen expression. However, cytotoxicity induced by rhIFN-gamma alone was also suppressed by rhIL-4 and TGF-beta 1, inferring that rhIFN-gamma-mediated abrogation of rhIL4 suppression was not simply a direct IL-2-independent effect on cytotoxicity. In addition, rhIL-4 did not increase TGF-beta production from rhIL-2-activated peripheral blood mononuclear cells, suggesting that rhIL-4 did not mediate reduction of rhIL-2 responses through the induction of TGF-beta release.

MHC restricted and non-restricted killer lymphocytes

Cytotoxic lymphocytes are either MHC-restricted (cytotoxic T-cells) or nonrestricted (natural killer NK-cells), although cells of the monocyte/macrophage lineage are also cytotoxic, and lymphocytes or phagocytic cells expressing Fc-receptors for immunoglobulin can function as antibody-dependent killer cells (referred to as antibody-dependent cellular cytotoxicity: ADCC). Antigen-specific T-lymphocytes recognise their target antigen in the context of MHC class I components, focusing their attack only against those cells expressing the relevant antigen specificity on their cell surface. A more primitive and alternative mechanism exists whereby NK-cells, classified as large granular lymphocytes (LGL), are able to kill in a non-specific manner, not requiring prior sensitisation to antigen. Both antigen-specific T-cells and LGL mediate their cytotoxicity through the release of cytotoxic molecules at the target-effector cell interface. LGL also have a regulatory role in the immune system through the release of cytokines, and can be distinguished from T-lymphocytes by the expression of distinct phenotypic markers (CD16+, CD56+) and they lack CD3 antigen expression or rearranged alpha/beta or gamma/delta T-cell receptor gene products. Cytotoxic activity is positively regulated by interleukin-2 (IL-2) and interferon (IFN), whilst prostaglandins and transforming growth factor-beta (TGF beta) diminish activation and effector pathways. Cytotoxicity mediated by NK- and T-cell populations are principally involved in the defence against microbial infections and neoplasia; the abrogation of cytotoxicity either by direct interaction of 'suppressor factors' with effector cells, or indirectly by reducing cytokine production can inevitably lead to the proliferation of the disease.