Norbert Fuchsberger

Anti-interleukin-8 activity of tick salivary gland extracts

Interleukin‐8 (IL‐8) is one of many mammalian chemokines (chemotactic cytokines) that direct mammalian inflammatory and immune cells to sites of injury and infection. Chemokines are produced locally and act on leucocytes through selective receptors. The principal role of IL‐8 is to control the movement and activity of neutrophils. To date, several tick species have been shown to modulate the production or activity of certain cytokines but none of these are chemokines. Using an IL‐8 specific ELISA, we showed that salivary gland extracts (SGE) from several ixodid tick species (Dermacentor reticulatus, Amblyomma variegatum, Rhipicephalus appendiculatus, Haemaphysalis inermis and Ixodes ricinus) reduced the level of detectable IL‐8. Analyses of fractionated SGE revealed one similar peak of activity for D. reticulatus, A. variegatum and R. appendiculatus; a second peak, observed for D. reticulatus and A. variegatum, differed between the two species. Using radiolabelled IL‐8, SGE and peak activity fractions of D. reticulatus were shown to bind the chemokine, and to inhibit binding of IL‐8 to its receptors on human granuolocytes enriched for neutrophils. The biological significance of these observations was demonstrated by the ability of SGE to inhibit IL‐8 induced chemotaxis of human blood granulocytes. Future isolation and characterization of the active molecules will enable determination of their functional roles in bloodfeeding and effect on tick‐borne pathogen transmission.

Ixodid tick salivary gland extracts inhibit production of lipopolysaccharide-induced mRNA of several different human cytokines

Extracts prepared from the salivary glands (SGE) of partially fed adult female Rhipicephalus appendiculatus ticks reduced the expression by human peripheral blood leukocytes (PBLs) of lipopolysaccharide (LPS)-stimulated cytokine mRNA. Treatment with SGE had no obvious effect on cytokine mRNA production when compared with untreated PBLs. LPS treatment induced or increased mRNA production for IFNα, IFNγ, TNF-α, IL-1α, IL-1β, IL-5, IL-6, IL-7 and IL-8. All the LPS-stimulated cytokine mRNAs were reduced when treated with a mixture of LPS and SGE. The results indicate the potential of ticks in modulating the cytokine network of their vertebrate hosts, possibly to facilitate blood feeding.

Tick salivary gland extracts promote virus growth in vitro

Saliva of blood-feeding arthropods promotes infection by the vector-borne pathogens they transmit. To investigate this phenomenon in vitro, cultures of mouse L cells were treated with a salivary gland extract (SGE) prepared from feeding ticks and then infected with vesicular stomatitis virus (VSV). At low input doses of VSV, viral yield was increased 100-fold to 10,000-fold by 16-23 h post-infection compared with untreated cultures, and depending on the SGE concentration. SGE-mediated acceleration of viral yield corresponded with the earlier appearance of VSV nucleocapsid protein as detected by 2-dimensional electrophoresis of infected cells. The observation that physiological doses of virus (i.e. doses likely to be inoculated by an infected arthropod vector into its vertebrate host during blood-feeding) respond to SGE treatment in vitro provides a new opportunity for identifying the factors in tick saliva that promote virus transmission in vivo.

Heterogeneity in the effect of different ixodid tick species on human natural killer cell activity

Tick saliva plays a vital role in blood‐feeding, including manipulation of the host response to tick infestation. Furthermore, a diverse number of tick‐borne pathogens are transmitted to vertebrate hosts via tick saliva, some of which exploit the immunomodulatory activities of their vector’s saliva. We report that salivary gland extracts (SGE) derived from Dermacentor reticulatus adult ticks induce a decrease in the natural killer (NK) activity of effector cells obtained from healthy human blood donors. The decrease was observed with SGE from both female and male D. reticulatus fed for either 3 or 5 days on mice, but no significant effect was observed with SGE from unfed ticks or ticks that had fed for 1 day. These results indicate that the tick anti‐NK factor(s) is only active after blood‐feeding has commenced. Microscopic examination revealed that the first step of NK activity, namely effector/target cell conjugate formation, was affected by SGE. The observed reduction in conjugate formation occurred when effector (but not target) cells were treated with SGE for 30 min, and the effect persisted after 12 h of treatment. Similar but less potent anti‐NK activity was detected for SGE from Amblyomma variegatum and Haemaphysalis inermis. By contrast, SGE derived from Ixodes ricinus and Rhipicephalus appendiculatus female ticks did not decrease NK activity. The apparent absence of such activity in these two important vectors of tick‐borne viruses suggests that control of NK cells does not play an important role in promoting virus transmission, at least for these particular species.

Electrophoretic Profiles and Activities of Human Interferon in Heterologous Cells

Human leukocyte interferon (IF) was found active in homologous human and heterologous rodent cells both in antiviral tests and in tests measuring cell-growth inhibitory activity. About 10 times more u

THE CELL GROWTH INHIBITORY AND ANTIVIRAL EFFECTS OF INTERFERON IN CLONED TRANSFORMED MOUSE CELLS

Eight clones and two subclones of SV40- and seven clones and one subclone of 20-methylcholanthrene-transformed C3H mouse embryonic fibroblasts were compared in tests for sensitivity to the antiviral and cell-growth inhibitory activities of a partially purified mouse L-cell interferon. While the sensitivity of clones and subclones to the antiviral activity of interferon was comparable to that of parent lines, the cell-growth inhibitory activity of interferon in the SV40 clones showed more than 100-fold variation and the methylcholanthrene-transformed cells could be divided into two groups in this respect. No correlation of sensitivity to the cell-growth inhibitory effect of interferon with the chromosome number, interferon-producing capacity or tumorigenicity of the clones could be detected. However, the cells of the interferon-sensitive clones No. 36 of the methylcholanthrene-transformed line were destroyed by macrophages at higher percentage binding of 125I-labeled soybean lectin. These results suggest that (1) the cell-growth inhibitory effect of interferon might be mediated by a specific type of receptors, and (2) N-acetyl-galactosamine present on the surface of interferon-resistant cells in a higher concentration than on interferon-sensitive cells hinders the recognition of cells both by macrophages and by interferon.