Opposite effects of serotonin and interferon-alpha on the membrane potential and function of human natural killer cells.

In an earlier article, we reported that serotonin (5-hydroxytryptamine, 5-HT) inhibits the natural killer cell (NK) cytotoxicity of human whole blood in a dose-dependent manner and that natural human interferon-alpha (IFN-alpha) partially eliminates this effect. Because natural IFN-alpha might contain factors other than IFN, we repeated these experiments with recombinant human interferon-alpha (rhIFN-alpha) and separated blood lymphocytes enriched with NK cells and then demonstrated that IFN really is responsible for this effect. Furthermore, this investigation was carried out to clarify the mechanisms of the action of 5-HT and of rhIFN-alpha on NK cells. The inhibition of the cytotoxicity was pronounced when 5-HT was added at the onset of the cytotoxic assay, whereas the pretreatment of lymphocytes for 18 h only led to a slight inhibition. Moreover, rhIFN-alpha applied 1 h before or 1 h after the addition of 5-HT decreased the inhibitory effect of 5-HT. Flow cytometric analysis involving the use of a voltage-sensitive dye, oxonol, revealed that 5-HT depolarized, whereas rhIFN-alpha hyperpolarized the plasma membrane of the lymphocytes. Thus, it seems likely that the inhibitory effect of 5-HT on the cytotoxicity of peripheral human lymphocytes is due to the depolarization on the plasma membrane of the effector cells and that rhIFN-alpha antagonizes this ability via its hyperpolarizing activity.

Cross-reactivity between human adenoviruses in delayed-type hypersensitivity.

The aim of this study was to determine the antigen responsible for the induction of delayed-type hypersensitivity (DTH) by human adenoviruses (Ads). The estimation of DTH was based on measurement of the extent of swelling of the hind footpads of mice. CsCl density gradient-purified human Ad serotype 6 (Ad6) induced DTH in a dose-dependent manner. In Ad6-sensitized mice, DTH could be elicited by serotypes belonging to the same species of human Ads (types 1 and 5) and by a serotype (type 3) belonging to another species. Latex particles coated with purified hexon antigen prepared from Ad5 had the capacity to sensitize mice and elicit a DTH reaction. We suggest that, for serotypes belonging to species C, the cross-reactive highly conserved T cell epitope of the hexon protein might be responsible for the DTH induction, and furthermore the same epitope might result in the cross-reactivity between serotypes 3 and 6. The possible importance of these data is discussed in relation to human gene therapy through the application of Ad vectors.

Therapy-induced antibodies against the antiviral and antiproliferative effects of interferons in patients with chronic hepatitis C virus infection.

Sera from 86 patients with chronic hepatitis C virus (HCV) infection treated with recombinant interferons-alpha (rIFN-alpha) were screened for IFN-binding and antiviral effect-neutralizing antibodies. Out of the 61 patients treated with rIFN-alpha2b, 46% had binding and 28% had neutralizing antibodies. 44% of the 25 patients treated with rIFN-alpha2a developed binding antibodies and 24% had neutralizing antibodies. Contradictory data were observed concerning the appearance of anti-IFN antibodies and the outcome of IFN therapy. A significantly higher number of the patients with a sustained response to rIFN-alpha2b therapy formed antibodies than the number among the non-responder patients. At the same time, in the patients treated with rIFN-alpha2a, opposite data were found. The activity of the antibodies in some sera was studied against the antiproliferative effect of IFNs on Daudi cells by measuring the [3H]thymidine incorporation. The binding antibodies without neutralization of the antiviral effect of the IFNs inhibited the antiproliferative activity of the rIFNs, similarly to antibodies having both IFN-binding and antiviral effect-neutralizing capacities. At the same time, the antiproliferative effect of the natural IFN was less affected. It is suggested that the antiproliferative assay is more sensitive than the antiviral method for demonstration of the presence of antibodies exerting an inhibitory effect on the biological activities of IFN.