No abstract

MxA gene expression is known to be regulated tightly and exclusively by type I interferons (IFNs). The kinetics of MxA gene expression was analyzed in peripheral blood mononuclear cells from 11 healthy volunteers vaccinated with the 17-D strain of yellow fever virus. A reliable induction of MxA RNA and MxA protein was found in the absence of easily detectable serum IFN activity. Thus, steady-state MxA RNA levels were elevated 8-to 30-fold above prevaccination levels on day 5 after vaccination. The average increase of MxA protein was --50-fold. In contrast, no induction of MxA RNA or MxA protein was detectable in 3 similarly vaccinated controls who were immune because of previous vaccinations. The IFN marker 2'-5'-oligoadenylate (2-5A) synthetase known to react to both type I and type II IFNs showed a similar response but did not differentiate equally well between nonimmune and immune vaccinees. P2-microglobulin and neopterin reacted poorly, remaining at low levels within the normal range. These results demonstrate that MxA gene expression is a good marker for detecting minute quantities of biologically active type I IFN during viral infections.Interferons (IFNs) are produced in response to viral infection and contribute to host defense by establishing an antiviral state in target cells [I]. Viruses induce predominantly two classes of IFNs, namely IFN-a and IFN-{1, collectively called type I IFNs [2]. It is not always possible, however, to detect circulating type I IFNs in the serum of patients most likely because type I IFNs are produced early in infection and may no longer be present in later serum samples or may not be formed in detectable quantities. For example, serum IFN is not usually found in patients with acute viral hepatitis [3,4], although IFN-induced changes occur in the liver and are suggestive oflocal IFN production and action [5]. Therefore, more reliable alternatives to direct serum IFN measurements are needed.Several assays have been developed that are based on the capacity of IFNs to induce expression of IFN-responsive genes in peripheral blood mononuclear cells (PBMC). Increased levels of an IFN-induced gene product indicate that the cells have been exposed to IFN in vivo and are respond-

The murine Mx-1 protein is one of the best biochemically and functionally characterized interferon (IFN)-induced proteins that is necessary, and sufficient, for providing resistance to murine cells against viral influenza infection. Recently an intracellular human protein homologous to the murine Mx-1 protein has been identified by means of a specific monoclonal antibody. The restricted induction of this intracellular protein in human mononuclear cells (MNC) by various cytokines was investigated. MNC from 26 of 28 healthy people and 35 of 36 cancer patients before IFN-alpha therapy had no detectable Mx-homologous protein. Incubation of human MNC with IFN-alpha and IFN-beta for 24 h at different concentrations led to a dose-dependent induction of the Mx-homologous protein. All IFN-alpha or IFN-beta preparations tested were equally effective in eliciting this intracellular protein. IFN-gamma induced only 1% of the Mx amount elicited by type-1 IFN compared on a weight basis. Neither interleukin (IL) 1 nor IL3, IL4, IL5, IL6, tumor necrosis factor-alpha/beta, granulocyte colony-stimulating factor (CSF) or granulocyte macrophage-CSF at any of the concentrations tested were capable of eliciting any detectable amount of the Mx homolog, while IL2 was a poor Mx-homologous protein inducer. In the presence of high-titered IFN-alpha antisera both IL2 and IFN-gamma were unable to stimulate this protein, proving that IFN-gamma and IL2 indirectly induce the Mx homolog via IFN-alpha. Therefore, the human Mx-homologous protein is a strictly by type I IFN-regulated protein in human peripheral blood lymphocytes.

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were prepared and used to serotype 821 clinical isolates of S. aureus from four countries. The capsular polysaccharide-binding sites on the bacterial membrane were examined by transmission and scanning electron microscopy.

A 78-kD protein (p78) is induced in human cells in response to interferon (IFN). It appeared as a radioactive spot when newly synthesized proteins from IFN-treated human cells labeled with [35S]methionine were separated in a two-dimensional system and autoradiographed. p78 was induced by IFN-alpha in normal human fibroblasts, and in some, but not all, established human tumor cell lines. It has been purified to homogeneity from Namalwa cells induced by recombinant IFN-alpha. Mouse polyclonal and monoclonal antibodies specific to p78 have been produced which allowed its quantitative determination in a Western blot ELISA. Using this method it was also shown that although IFN-gamma was a poor inducer of p78, it markedly increased the effect of IFN-alpha on p78 induction and accumulation. It was also demonstrated that p78 and the protein Mx of influenza-resistant mice, which we purified and characterized earlier (Horisberger and Hochkeppel, J. Biol. Chem. 260, 1730-1733, 1985) share common properties such as size, pI, amino acid composition, antigenic determinant(s), and IFN inducibility.