A chemically-synthesized gene and natural complementary DNA coding for human lymphotoxin were isolated and engineered for expression in Escherichia coli. Purified recombinant lymphotoxin shows cytotoxic activity on murine and human tumour cell lines in vitro and causes necrosis of certain murine sarcomas in vivo.

The multiple biological activities present in semipurified lymphokine preparations have made it difficult to assign discrete biological functions to each lymphokine. As a result, the large number of identified lymphokine activities may actually reflect the manifestations of a few factors. While this research has also been hampered by the limited quantities of lymphokines available, hybridoma and recombinant DNA technologies have begun to help overcome these limitations.Macrophage activation has been intensively investigated because it is generally agreed that activated macrophages play an essential role in the defense against microorganisms and in the immune response against neoplasia (1). Macrophage activation mediated by macrophage activation factor (MAF) 1 and gamma interferon (IFN-'y) has been characterized by similar morphologic, metabolic, and functional changes (2-6) including stimulation of nonspecific tumoricidal activities (5), induction of Ia antigen expression (7, 8), increased Fc receptor expression (0, 10), production of plasminogen activator (I 1), and production of hydrogen peroxide (12). Several investigators (5,8,12,13) have postulated therefore that IFN-q~ and MAF may be identical. In support, Schreiber et al. (14) have recently demonstrated biosynthetic and biochemical similarities of IFN-'y and MAF produced by a murine T cell hybridoma (24/G1). Both the antiviral and MAF activities of 24/G1 cultured supernatants were neutralized by anti-IFN-% but not anti- . have demonstrated neutralization of MAF activity with polyclonal antMFN-7, definitive results could not be ascertained since these antisera were prepared from partially purified preparations and could contain antibodies that neutralize other lymphokine activities.In the present report, murine IFN-~ produced by recombinant DNA techniques (18) (>00% pure) was tested for MAF activity; special attention was given

Treatment of human peripheral blood lymphocytes with cloned N alpha-desacetylthymosin alpha 1 induced interferon production. The kinetics is similar to that of mitogen-induced interferon induction. N alpha-desacetylthymosin alpha 1, in combination with mitogen, augments the amount of interferon produced. This interferon is immune interferon (IFN-gamma) as determined by sensitivity to pH 2, lack of neutralization by antibodies to IFN-alpha or IFN-beta and absence of activity of MDBK cells. Although the mechanism of induction of IFN-gamma by N alpha-desacetylthymosin alpha 1 is unclear, this compound is not mitogenic at concentrations causing IFN-gamma production. These results indicate that thymic factors may also participate in the regulation of IFN-gamma-production.

The in vivo regulation of natural killer (NK) cell function by recombinant murine gamma interferon (rMuIFN-gamma) and recombinant human interleukin-2 (rHuIL-2) was investigated. Peritoneal exudate-derived natural killer (PE-NK) cells of mice treated with rMuIFN-gamma or rHuIL-2 exhibited significantly enhanced cytolytic activities against YAC-1 target cells. Compared with animals receiving treatment with either rMuIFN-gamma or rHuIL-2 alone, the sequential treatment of mice with both agents resulted in a significantly greater enhancement of PE-NK cell function, especially when rMuIFN-gamma was administered 24 h before treatment with rHuIL-2. The cytolytic activities were significantly diminished after pretreatment of effector cells with anti-Qa-5 antiserum and complement but not with anti-Lyt-3.2 antiserum. These data constitute the first evidence demonstrating the association between IFN-gamma and IL-2 in the regulation of NK cell function in vivo, reinforce the potential benefit of combined treatment with biological response modifiers, and show that the schedule of administration may be a critical requirement for optimal benefits of combined lymphokine treatment in vivo.

Recombinant human interferon-gamma (rHuIFN-gamma) and natural human tumor necrosis factor beta (nHuTNF-beta) (previously called lymphotoxin), purified to homogeneity, were used to assess their effects on certain functions of human polymorphonuclear neutrophils (PMN) in vitro. The treatment of PMN with 100 U of either rHuIFN-gamma or nHuTNF-beta for 20 min significantly increased their ability to phagocytize 1.5-microns latex beads as detected by flow cytometry. Preparations of recombinant human TNF-beta (rHuTNF-beta) showed activities similar to those of its natural counterpart in activating phagocytosis. In addition, a significant enhancement in PMN-mediated antibody-dependent cellular cytotoxicity was observed after treatment for 2 hr with IFN gamma and both TNF-alpha and TNF-beta. The enhancement by treatment with a combination of rHuIFN-gamma and nHuTNF-beta exceeded the enhancement caused by either agent alone. We also show that although lipopolysaccharide (LPS) is a potent stimulator of PMN function, polymyxin B can block LPS-induced but not lymphokine-induced activation. These data demonstrate new activities for both TNF-alpha and TNF-beta in augmenting the phagocytic and cytotoxic activities of PMN.