Is there an interleukin 2 inhibitor in human serum?

An examination of the immune system of the duck (Anas platyrhynchos) for factors resembling some defined mammalian cytokines

Duck lymphoblasts generated by phytohaemagglutinin (PHA) did not respond to recombinant or Jurkat cell line human interleukin (IL)-2 or possess surface antigens resembling mammalian IL-2 receptors or IL-1 beta. Supernatant fluids from normal and PHA-stimulated duck lymphocyte cultures, and normal and lipopolysaccharide (LPS)-stimulated monocytes, gave negative results in a range of assays for biological activity and immunochemical presence of factors resembling mammalian IL-1 and IL-2. However, supernatant fluids from LPS-stimulated duck monocytes contained IL-6-like activity (up to 35 units/mL) assessed on the 7TD-1 murine cell line. We were unable to demonstrate mRNA that would hybridize to cDNA probes for human IL-1 beta, IL-6, and tumour necrosis factor (TNF) in extracts of blood and lymphoid organs from normal and antigen-stimulated ducks. Because homologous serum or plasma is essential for duck lymphocytes and macrophages to respond to mitogens in vitro, we asked whether this growth-factor-like activity might be caused by substances resembling mammalian cytokines. Serum and plasma were examined for activity consistent with IL-1 and IL-6 on mammalian target cells. None was detected. Instead, both serum and plasma contained inhibitors of human IL-1 beta and IL-6, detected at dilutions up to 1:100. Inhibition by serum was heat (56 degrees C, 30 min) labile but inhibition by plasma was heat stable. The identities and biological functions of these inhibitors remain to be defined.

The so-called interleukin-2 inhibitory activity of human serum is largely cytotoxic to mouse cells

No specific interleukin-2 (IL-2) inhibitor has ever been demonstrated in human, mouse, or any other animal serum. Native mouse serum contains activities which completely inhibit IL-2-dependent and IL-2-independent in vitro proliferation of cells of different animal species by a non-cytotoxic mechanism. The decisive inhibitory component of mouse serum has a molecular weight of about 80,000, is heat-labile and has not been found in other animal sera. Also, native human serum completely suppresses the proliferation of various mouse cell types, predominantly by a cytotoxic effect caused by natural IgM antibodies and complement. Heat-inactivated human serum is no longer cytotoxic to mouse cells, and inhibits the proliferation of mouse cells much less than native serum. There is thus no evidence for a specific IL-2 inhibitor in mouse, human or other serum.

Evidence of a plasma-mediated "window" of immunodeficiency in rats following trauma

The etiology of immunodeficiency following trauma was investigated. Plasma collected from Fischer rats 1-8 hr following a 40% surface area thermal injury (TI) displays immunosuppressive activity (ISA). Peak ISA (4 hr) exceeded 90% inhibition of Con A3-induced proliferation of normal spleen cells. Splenic macrophage IL-1 secretion and NK activity are also inhibited by 4-hr TI plasma. Most importantly, these same cellular immune functions decline in rats by 4 hr following TI. After a further decline by 16 hr (IL-1 = 19.8% and NK activity = 40% of normal), these cellular immune functions rebound toward normal values by 2 days following TI. Thus, ISA in plasma is both temporally and functionally linked to the cellular immune defects observed. Sham-treatment rats display a similar, although less marked, pattern of plasma-linked transient cellular immune defects indicating a role for stress in these responses. ISA is abolished by mild heat (56 degrees C for 30 min) and wholly contained in the greater than 10-kD fraction of plasma. Together, these results provide evidence that previously unrecognized molecules in plasma induce a "window" of immunodeficiency early following trauma.

In vivo activation of lymphocytes in melanoma patients receiving escalating doses of recombinant interleukin 2

A phase-I study of the recombinant, non-mutagenized interleukin 2 (rIL2, BioleukinTM) was performed in 12 melanoma patients (Pts). From 100 to 800 micrograms/m2 of rIL2 were administered by i.v. bolus injection, TID for 4-8 days. Side-effects included fever, malaise, low serum K+ and Ca++ values, electrocardiographic abnormalities, leukopenia and thrombocytopenia. No major organ toxicity and no significant fluid retention were observed at the administered doses. Treatment induced a rapid depletion of peripheral blood lymphocytes (PBL) with a rebound (2-6 times the pre-treatment values), 24-48 hr after rIL2 discontinuation. PBL obtained between the 5th treatment day and the 2nd post-treatment day showed: (a) enhanced proliferation (II/12 Pts) with stimulation indexes of 6-52; (b) increased cytotoxicity against autologous tumor cells (2/2 Pts), allogeneic melanomas (5/7 Pts), the Daudi (5/6 Pts) and K562 cell lines (7/12 Pts); and (c) increased expression of IL2 receptors (8/12 Pts) and of DR antigens (6/12 Pts). Lymphocytes collected 1-2 days after treatment and activated in vitro with rIL2 showed a more rapid development of tumor cytotoxicity, with an earlier loss of activity. Spontaneous proliferation, autologous or allogeneic tumor cytotoxicity and expression of IL2 receptors obtained after in vivo treatment with rIL2 were significantly weaker than those induced during in vitro stimulation. No major objective responses were detected in these patients.

Decreased level of thymidine in the serum of obese strain (OS) chickens with spontaneous autoimmune thyroiditis

We have previously shown that normal chicken serum (NCS) is able to interfere with the IL 2 promoted incorporation of DNA precursors into T lymphoblasts and that serum derived from autoimmunity prone Obese strain (OS) chickens is deficient in this respect. This "defect in non-specific suppression" has been speculated to be one of the causes for T cell hyperreactivity in the OS. In this study we present several lines of evidence that the suppressive effect of normal chicken serum (NCS) on 5-(125Iodo)-2-deoxyuridine (125IUdR) uptake into chicken T blasts is a competition artefact due to cold thymidine (TdR) present in NCS. Inhibition of 125IUdR required the continuous presence of NCS and suppression of 3H-TdR incorporation could be competed for by increasing the dose of the radiolabel. Molecular sieve chromatography followed by reversed phase high performance liquid chromotagraphy revealed the "inhibitory" activity to co-elute with TdR. Moreover, NCS did not suppress protein synthesis by chicken T cells growing with IL 2 and did not affect oxidative metabolism, cell viability, expression of IL 2 receptors, or percentages of cells in the S phase of the cell cycle. In accordance with these data, OS-sera suprisingly contain less TdR than those from normal controls. Experiments involving crosses of the OS with the normal inbred CB strain, revealed that the subnormal serum TdR level of the OS is an autosomally dominant trait which, however, segregates from T cell hyperreactivity. These findings falsify our previous hypothesis that a defect in specific IL 2 antagonists might be involved in T cell hyperfunction of the OS and indicate that NCS is devoid of factors which neutralize IL 2 function.