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A method for in situ protein immunodetection using a peroxidase labeling system is described for detecting functional and structural proteins encoded by potato virus Y (Tunisian isolate) in plant tissues. Such Potyviruses are characterized by the accumulation of inclusion bodies containing viral encoded proteins other than coat protein. These proteins are functional at early stages of infection, making them easy to detect. Data are compared to those obtained by immunofluorescence techniques. Our technique can be used as a preliminary method for rapid detection of virus infection using antibodies directed against functional proteins.

A partially purified nuclear inclusion (NI) fraction was obtained from tobacco plants infected by potato virus Y (PVY). Four monoclonal antibodies (MAbs) were produced and characterized using this semipurified fraction as antigen. Data showed that only one was directed against NIa whereas two were directed against cytoplasmic inclusion (CI) protein and the last one against coat protein (CP). These results were due to the fact that the semipurified NI fraction was usually contaminated with CI and CP proteins. When used on in situ immunofluorescence method the anti-NIa MAb showed accumulation of the NIa protein in both nucleus and cytoplasm. In vivo, this MAb was able to detect different forms of the NIa protein including precursors and cleavage products. It was also able to inhibit the cleavage of the polyprotein detected in the semipurified NI.

The human IgA2 subclass has two allotypes A2m(1) and A2m (2). Using the RFLP technique, we determined the A2m(2) frequency in a sample of 29 tunisian individuals. In accordance with Lefranc and all. [6], the presence of a polymorphic EcoRI site of the A2m(2) allele was confirmed in our RFLP study whereas no BamHI nor HindIII polymorphisms were shown. Among the 29 cases studies, 11 were heterozygous A2m2-1, 17 homozygous A2m1-1 and 1 homozygous A2m2-2. The A2m2 allele frequency in the Tunisian population (0,22) is intermediate between the European frequency and the African one.