Estudo comparativo da resposta imunológica induzida em camundongos por vírus que infectam plantas

Abstract

Some viruses of plants have been shown to be useful for the expression of antigens in the production of vaccines. The present work is a comparative study of the immunogenic capacity of the following viruses: Tobacco mosaic virus-TMV, Cucumber mosaic virus-CMV, Squash mosaic virus-SqMV and Cowpea aphid-terminal mosaic virus-CABMV in mice immunized by the subcutaneous, oral and nasal routes. After purification, TMV, CMV, SqMV and CABMV, were spectrophotometrically analyzed and they presented curves characteristics of their genera or families. These viruses in the native form, inoculated in Chenopodium amaranticolor, induced local necrotical lesions and by electroforetic analysis it was shown that, the capside of TMV, CMV and CABMV just presented protein bands with apparent molecular masses of 17, 29 and 35 kDa respectively. Concerning the SqMV it presented two protein bands with apparent molecular masses of 21 and 43 kDa. All the viruses, except CABMV, after inactivation at 100 °C for 10 min, showed the same protein bands they had prior the thereto-inactivation. However, there was a loss of the infectant capacity of the virus since none of them caused local necrotic lesions in C. amaranticolor. Apparently, the three-dimensional structures of the viral capside of the plant viruses play a fundamental role in the preservation of the functional integrity of the nucleic acids of the viruses that cause diseases in the infected plants. The immunogenic capacity of those viruses was tested in mice by different routes. TMV in the native form was able to induce immune response in "swiss" mice immunized by the subcutaneous, oral and nasal routes. The immunization through the subcutaneous route, in presence of AI(OH)3, revealed that the adjuvant effect depends on the method of evaluation of the titles of specific antibodies. CMV and SqMV, in the native form, induced immune response in mice immunized by the oral and nasal routes. All the viruses, TMV, CMV and SqMV, lost their infectant and immunogenic capacity capacities after thermo-inactivation. Immunogenic response was not detected against the proteins of the extract of leaves of N. benthamiana, host-plant of TMV, in spite that a immune response has been detected by TMV, when the extract of TMV infected leaves was used to induce immunization in the mice by subcutaneous and oral routes. Synthesis of specific IgE was not detected in mice immunized by subcutaneous and oral routes, nor with native TMV, nor with extract of leaves infected by this virus. Similarly, specific lgE synthesis was not detected with CMV and SgMV immunized mice by oral and nasal routes. The results of the evaluation of the immunogenic capacity of CABMV were not conclusive. TMV, by its characteristics is a preferential virus for immunization through the subcutaneous, oral and nasal routes. CMV showed a tendency to induce better immune response by oral route and SqMV by the nasal one. Apparently, the immunogenic capacity of the vegetable viruses is related to the structure of the viruses. However, further experiments are still required. Furthermore, viruses of plants seem to be endowed with special properties that turn them candidates to future use in Immunization/vaccination procedures.