New in vitro method for evaluating antiviral activity of acyclic nucleoside phosphonates against plant viruses.

A new method was developed for testing antiviral compounds against plant viruses based on rapidly growing brassicas in vitro on liquid medium. This method enables exchange of media containing tested chemicals in various concentrations and simultaneous evaluation of their phytotoxicity and antiviral activity. While using ribavirin as a standard for comparison, phytotoxicity and ability of the acyclic nucleotide analogues (R)-PMPA, PMEA, PMEDAP, and (S)-HPMPC to eliminate ssRNA Turnip yellow mosaic virus (TYMV) were evaluated by this method. Double antibody sandwich ELISA and real-time PCR were used for relative quantification of viral protein and nucleic acid in plants. Ribavirin had the most powerful antiviral effect against TYMV. On the other hand, (R)-PMPA and PMEA had no antiviral effect and almost no phytotoxicity compared to the control. (S)-HPMPC and PMEDAP showed moderate antiviral effect, accompanied by higher phytotoxicity. The tested compounds can be screened within 6-9 weeks in contrast to the 6 months for traditionally used explants on solid medium. The method enables large-scale screening of potential antivirals for in vitro elimination of viruses from vegetatively propagated crops and ornamentals.

Acquired resistance of pigeons to Argas polonicus larvae.

The acquired resistance of pigeons to Argas polonicus manifests itself in an adverse effect on the feeding and further development of larvae. After five subsequent infestations, the rejection of larvae reached 90-95% and the mean weight of fed larvae dropped down from 2.18 mg to 1.72 mg in the Polish tick population. There appeared also a tendency to more rapid feeding in larvae from later infestations. Also the percentage of moulted larvae decreased, probably as a result of insufficient blood meal taken by larvae on repeatedly challenged hosts. The hosts sensitized by larvae of Polish tick population manifested a higher tick resistance than those sensitized by larvae of Czechoslovak population. No adverse effect has been observed in males and females after repeated infestation of sensitized pigeons. Anti-tick antibodies were detected in the serum of pigeons sensitized by larvae with the aid of counter current immunoelectrophoresis using extracts from whole larvae and from salivary glands of adults as antigen. No antibodies were detected in the serum of pigeons sensitized by adult ticks.

Cutaneous and blood leucocyte response of pigeons to larval Argas polonicus feeding.

Dynamics of granular leucocyte response in peripheral blood of naive and sensitized pigeons infested with Argas polonicus larvae was only slightly dissimilar. In both cases a marked increase of heterophil and eosinophil counts and only a mild increase of basophil count were recorded at 6 hours post-infestation. In naive hosts the basophil count increased again at 96 hours post-infestation, but in sensitized hosts it did so as early as 48 hours post-tick attachment and was also accompanied by an increase of eosinophil levels 72 and 96 hours post-infestation. Cutaneous response of sensitized hosts at the tick feeding site was characterized by a large heterophil accumulation at 24 hours post-infestation, by an increased eosinophil count at 48 hours and basophil counts at 72 and 96 hours post-infestation. In primary hosts lesions were characterized by a mild increase of heterophil count later than 48 hours post-infestation and by slight eosinophil accumulations at 24 and 48 hours post-tick attachment, as well as basophil accumulation as late as 96 hours post-infestation. Cutaneous lesions of sensitized hosts were accompanied by apparent inflammatory changes which were mild and sometimes missing in primary hosts. Cytotoxic and degenerative alterations of basophils and other granulocytes were observed as well as vesiculation of secretory granules of basophils. Cutaneous response of sensitized hosts to larval A. polonicus feeding can be characterized as a cutaneous basophil hypersensitivity.