During a sublethal murine infection with Listerid monocytogenes cells, tumor necrosis factor (TNF) activity was detectable in neither sera nor spleen homogenates at any stage of the infection when a bioassay with L-929 cells (<4 U/ml) was used. However, injecting the mice with an immunoglobulin fraction obtained from a rabbit hyperimmunized with recombinant murine TNF-a resulted in acceleration of listeriosis. When 1 mg of anti-TNF antibody was injected per mouse, all the mice died from listeriosis, even though the infectious dose was sublethal for the untreated controls. The antigen-specific elimination of the bacterium from the spleens and livers of anti-TNF antibody-treated mice was delayed, depending on the dose of the antibody injected. Endogenous TNF seemed to be produced early in infection, because suppression of antiisterial resistance was significant when a single injection of anti-TNF antibody was given between day zero and day 2 of infection. The effect of endogenous TNF on antilisterial resistance was due to neither regulation of alpha interferon (IFN-a) * Corresponding author. ably due to the induction of both TNF receptor expression and the accumulation of mRNA for TNF by IFN-y (6, 35). Furthermore, the increased expression of major histocompatibility complex class I antigens by TNF is reported to be mediated by TNF-induced IFN-3 subtype 1 (IFN-fi1) or 0.01 M phosphate-buffered saline (PBS; pH 7.4).

The choice of the type of instrument to measure delayed-type hypersensitivity (DTH) in mice, as assayed by ear swelling reactions, influences the experimental results. When a caliper that applies little pressure to the ears is employed, DTH reactions in ears of mice sensitized to picryl chloride show an early onset at 2 h after challenge, comparable swelling at 4 h and a slow rise to a 24 h classical peak response thereafter. In contrast, 3 different micrometers that apply more pressure to the ears reveal a biphasic pattern of ear swelling reactions in mice immunized and challenged with picryl chloride. The early component of DTH measured by these micrometers peaks 2 h after challenge. Thereafter the measured ear thickness declines, and the onset of the classical delayed reaction is detected at 12 h after ear challenge. Yet another instrument, that in contrast to the caliper and micrometers mentioned above, applies all the pressure to only a very restricted area of the ear, fails to detect an early swelling reaction; the delayed reaction is first detected at 12 h after ear challenge and rises thereafter to a 24 h peak.The differences in outcome of the assays using the different instruments indicate that the early component or DTH reactions differs from the late component of DTH reactions in that the early swelling is easier to compress when pressure is applied by the instrument used for measurement. This is probably caused by the fact that the late reactions are due to a cellular infiltrate, whereas the early reactions are edematous in character, and are due to accumulation of plasma components.

The resistance in mice against Listeria infection was augmented by treatment with recombinant human tumor necrosis factor (TNF). To elucidate this phenomenon, we examined the effect of TNF on macrophage activation. TNF-treated macrophages had listericidal activity in vitro and superoxide anion production. In addition, macrophage migration was inhibited in the presence of TNF. Therefore, activation of macrophages by TNF was similar to activation by macrophage-activating factor or macrophage-migration-inhibitory factor.

The significance of interferons (IFNs) induced by Listeria monocytogenes in the antilisterial defense mechanism was studied in mice. Cyclosporin A (CsA) had no effect on IFN-alpha production that was induced in the bloodstream after intravenous infection of mice with L. monocytogenes, whereas IFN-gamma that was induced in the bloodstreams of control mice 6 h after stimulation with specific antigen in the late phase of infection was suppressed in CsA-treated mice, depending on the dose of the drug injected. The decrease in IFN-gamma production caused an increase in bacterial growth in the spleens and livers of CsA-treated mice. Furthermore, administration of a daily dose of CsA at 80 or 100 mg/kg of body weight resulted in fatal listeriosis, even though the dose was nonlethal for normal mice. The administration of recombinant murine IFN-gamma on day 0 of L. monocytogenes infection prevented CsA-treated mice from developing fatal listeriosis and restored their ability to produce IFN-gamma in the bloodstream, in response to specific antigen in the late phase of infection.

This report describes an activity in serum from mice that were contact-sensitized with picryl chloride (PCl) 1 to 4 days earlier. Immune serum, when given i.v., transfers the ability to elicit an immediate hypersensitivity-like ear swelling reaction in naive recipients following local challenge with PCl. This serum activity is due to an antigen-binding T cell factor that shares some properties with IgE antibody. The activity is antigen specific, and due to an antigen-binding moiety that is heat labile (56 degrees C, 4 h). However, unlike IgE antibody the serum activity is resistant to reduction and alkylation, and is retained by columns of Sepharose beads coupled with polyclonal or monoclonal antibodies that react with antigen-specific T cell factors from other systems. These columns did not retain IgE antibody activity in our experiments. Importantly, the serum activity was not retained by columns linked with antibodies directed to mouse immunoglobulins, which do retain IgE activity. We conclude from these data that the activity in PCl immune serum is not caused by IgE antibody, and is due to the presence of the previously described antigen-specific T cell factor (PCl-factor), that can activate serotonin-containing cells, such as mast cells, to release the vasoactive amine serotonin. PCl-factor transfers the ability to elicit an immediate hypersensitivity-like reaction that is an early component of delayed-type hypersensitivity. The presence of this T cell factor in the serum of actively sensitized mice provides a means to sensitize tissues throughout the body for this required, initial, serotonin-dependent component of delayed-type hypersensitivity reactions.