Recombinant E2 glycoprotein of bovine viral diarrhea virus induces a solid humoral neutralizing immune response but fails to confer total protection in cattle

Two recombinant baculoviruses were produced in order to obtain a bovine viral diarrhea virus (BVDV) immunogen: AcNPV/E2 expressing E2 glycoprotein, and AcNPV/E0E1E2 expressing the polyprotein region coding for the three structural proteins of BVDV (E0, E1, and E2). Mice were immunized with Sf9 cells infected with the recombinant baculoviruses in a water in oil formulation and the production of neutralizing antibodies was evaluated. Since E2 elicited higher neutralizing antibody titers than E0-E1-E2 polyprotein, it was selected to immunize cattle. Calves received two doses of recombinant E2 vaccine and were challenged with homologous BVDV 37 days later. The recombinant immunogen induced neutralizing titers which showed a mean value of 1.5 ± 0.27 on the day of challenge and reached a top value of 3.36 ± 0.36, 47 days later (84 days post-vaccination). On the other hand, sera from animals which received mock-infected Sf9 cells did not show neutralizing activity until 25 days post-challenge (62 days post-vaccination), suggesting that these antibodies were produced as a consequence of BVDV challenge. Even when no total protection was observed in cattle, in vitro viral neutralization assays revealed that the recombinant immunogen was able to induce neutralizing antibody synthesis against the homologous strain as well as against heterologous strains in a very efficient way.

Magnitude, duraçäo e especificidade da resposta sorológica em bovinos vacinados contra o vírus da diarréia viral bovina (BVDV) / Magnitude duration and specicicity of the serological response in cattle vaccinated against bovine viral diarrhea virus (BVDV)

A resposta sorológica induzida por três vacinas comerciais inativadas contra o vírus da Diarréia Viral Bovina (BVDV) foi avaliada em bovinos imunizados três vezes (dias 0, 30 e 180) e testados a diferentes intervalos após a vacinaçäo. Trinta dias após a segunda vacinaçäo, 74,5 por cento (70/94) dos animais apresentavam anticorpos neutralizantes contra o BVDV-1 e 52,1 por cento (49/94) contra o BVDV-2. Os títulos médios (GMT) e o número de animais reagentes contra o BVDV-1 eram de 109,3 (32/36); 54,6 (22/28) e 25,5 (16/30) para as vacinas A, B e C, respectivamente; e de 19 (27/36), 42,3 (12/28) e 18,4 (10/30) contra o BVDV-2. Os títulos reduziram-se aos 180 dias, sendo que 31,9 por cento (30/94) dos animais já näo apresentavam atividade neutralizante frente ao BVDV-1 e 63,8 por cento (60/94) frente ao BVDV-2. Nesta data, os títulos médios e o número de animais positivos frente ao BVDV-1 eram de 28,3 (30/36), 28,3 (20/28) e 16,1 (14/30) e frente ao BVDV-2 de 16,8 (18/36), 21,6 (10/28) e 28,3 (6/30) para as vacinas A, B e C, respectivamente. Após o reforço (dia 180), os títulos médios contra o BVDV-1 aumentaram significativamente nos três grupos vacinais e contra o BVDV-2 apenas no grupo A. Trinta dias após, os títulos médios e o número de reagentes contra o BVDV-1 eram de 104,8 (23/24), 50,3 (24/26) e 43,7 (24/28) e contra o BVDV-2 de 33,4 (23/24), 23,3 (22/26) e 15,7 (22/28) para as vacinas A, B e C. Os títulos contra o BVDV-1 no dia 210 foram estatisticamente superiores aos títulos contra o BVDV-2 nos três grupos vacinais. O soro de alguns animais positivos de cada grupo foi testado frente a quatro amostras brasileiras de BVDV-1 e duas de BVDV-2. Além dos títulos baixos a moderados, os testes de neutralizaçäo cruzada revelaram variaçöes marcantes na atividade neutralizante frente a isolados de campo antigenicamente diferentes. Esses resultados demonstram que a vacinaçäo näo induziu uma resposta sorológica de magnitude e duraçäo adequadas na maioria dos animais, principalmente frente à grande diversidade antigênica das amostras de BVDV.

Humoral immune response anti K99 pilus from enterotoxigenic Escherichia coli in experimentally inoculated calves

The bovine model is extremely interesting to study several basic aspects of mucosal local immunity. Many reports have shown that, in young calves, the infectivity of enterotoxigenic Escherichia coli may be inhibited by passively administered antibodies anti K99 pilus. We have measured, by immunoradiometric assays, the IgG response anti K99 pilus in the serum of calves, deprived of colostrum and orally inoculated with enteropathogenic K99+ E. coli. Although variable levels of IgG anti K99 pilus were detected, their protective value could not be ascertained in vivo due to the acute development of the infection. In an effort to correlate the presence of serum antibodies anti K99 pilus with their protective capacity, an ex-vivo assay to monitor the interaction of radiolabeled K99 pilus with the bovine mucosa was standardized. Paradoxically, although K99 pilus, purified by standard procedures, was recognized by polyclonal rabbit and calf antisera, its interaction with the bovine intestinal mucosa, quantitated in the ex-vivo system, was not inhibited by these reagents, indicating that the antibodies did not effectively block those K99 pilus domains involved in the interaction with mucosal receptors

Inmunidad pasiva contra infecciones virales entéricas: rotavirus bovino / Passive inmunity against enteric infections: bovine rotavirus

Enteric viral infections in calves are widespread and most occur as enzootics in calves under 3 weeks of agne. Both clinical and subclinical infections occur, with the severity of the disease influenced by such factors as the level of passive immunity and the challenge dose and strain of virus. Rotaviruses and coronaviruses are primary enteric viral pathogens commonly associated with the neonatal calf diarrhea syndrome. Rotaviruses and coronaviruses replicate in intestinal villous enterocytes, resulting in villous atrophy and consequently a malabsorptive diarrhea. Two vaccination approaches have been developd to try to prevent rotavirus and coronavirus infections in calves. The first involves administrtion of modified live rotavirus and coronavirus to newborn calves to stimulate active immunity. This procedure was not efficacious under field conditions, presumably due to the widespread presence of maternal antibodies which neutralize the vaccine viruses. The second approach relies on rotavirus and coronavirus vaccination of cows to enhance antibody titers in mammary secretion and thus provide passive immunity. The variables involved in this latter approach using bovine rotavirus as a model are defined in this report. An analyses of passive and active immunity in calves supllemented with colostrum from rotavirus vaccinated cows and challenged by rotavirus is also desribed. Results indicate that a commercial vaccine failed to increase rotavirus antibody titers in mammary secretions, but experimental vaccines developed in this laboratory significantly increased such titers. Furthermore, passive protection against rotavirus was mediated by optimal levels of colostral rotavirus antibodies, primarily of the IgGl class, present at frequent intervals within the calfs intestine (lactogenic immunity). Serum antibodies alone in the newborn calf were less protective, but may moderate the severity of rotavirus infecctions