Dynamics of ex vivo cytokine transcription during experimental Toxocara canis infection in Balb/c mice

The cytokine microenvironment is crucial in generating and polarizing the immune response. A means of monitoring this environment would be of great value for better understanding Toxocara canis immune modulation. The aim of this study was to analyze the dynamics of cytokine transcription ex vivo, during early (24-48 hours) and late (15-30 days) times post-infection, in the mesenteric lymph nodes, spleen and intestinal mucosa of Balb/c mice experimentally infected with T. canis larvae. Mice in the treated group were infected with 100 third-stage larvae (L3), whereas mice in the control group were not infected. Analyses were performed at different times: 24-48 hours post-infection (HPI), 15-30 days post-infection (DPI). IL4, IL10, IL12 and Ym1 mRNA transcriptions were analyzed through qPCR. This study showed cytokine transcription mediated by migrating larvae in the mesenteric lymph nodes and spleen at 24-48 HPI, whereas cytokine transcription in the intestinal mucosa was observed only at late times (15-30 DPI). These results suggest that the T. canis larvae migration during infection might play a role in cytokine dynamics. Since the cytokine microenvironment is crucial in modulating immune response, knowledge of cytokine dynamics during T. canis infections pave the way to better understand its interaction with the host.

Infectious Bronchitis Virus Vaccination at Day 1 of Age Further Limits Cross Protection

Cross-protection and immune responses elicited by infectious bronchitis virus (IBV) vaccination on Day 1 of age or at later time points were examined. Specific-pathogen-free chickens were vaccinated with a Massachusetts-type vaccine and heterologous challenge was performed with an Arkansas (Ark) -type virulent strain. In Trial 1, chickens vaccinated on Day 1 or Day 10 of age were challenged 21 days after vaccination. Analysis of tracheal histopathology and viral load demonstrated less cross protection when vaccination was performed on Day 1 of age. In Trial 2, chickens were vaccinated on Day 1 or Day 14 of age. A somewhat stronger systemic antibody response to IBV was detected in chickens vaccinated at 14 days of age. In addition, avidity of antibodies to Ark-type S1 protein elicited by vaccination at 14 days of age was greater. Differences in immune-cell populations in the Harderian gland (HG) observed at the time of sampling (35 days following vaccination) between chickens vaccinated at 1 day or 14 days of age indicated greater, rather than reduced, immune activity in the chickens vaccinated at 1 day of age. These differences are, perhaps, a result of the higher levels of persisting vaccine virus observed in the younger chickens. Both nonvaccinated/challenged groups showed significantly higher (P < 0.05) proportions of B cells and CD8⁺ T cells 7 days after challenge than age-matched vaccinated/challenged groups or age-matched nonvaccinated/nonchallenged control groups. These results indicate infiltration and/or expansion of B cells and CD8⁺ cells in HGs following challenge of nonvaccinated chickens. A fortuitous finding was that the more immature immune system of chickens vaccinated at 1 day of age was less effective at clearing vaccine virus after vaccination. Collectively, the current results indicate that IBV vaccination at 1 day of age can decrease the potential for heterologous cross protection compared with vaccination at least 10 days after hatch. A lower level of antibody affinity maturation likely contributes to decreased cross protection.

Early Vaccination of Chickens Induces Suboptimal Immunity Against Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) is highly prevalent in broiler chickens despite extensive vaccination commonly conducted early after hatch. The effects of early vaccination on immune responses were further investigated in chickens primed at increasing ages, followed by booster vaccination with an attenuated Arkansas (Ark) Delmarva Poultry Industry-type vaccine. Results show that vaccination on day 1 of age elicits significantly lower systemic and mucosal antibody responses compared with vaccination at later time points in the life of the chicken. The increase of IBV antibodies in serum from secondary responses after booster vaccination was more dramatic and significantly higher when measured by an Ark spike subunit 1 protein ELISA compared with measuring by non-Ark serotype whole-virus ELISA, which underlines the immunogenic importance of the virus spike at inducing antibodies. However, the levels achieved following boosting did not differ significantly between ages of priming. Thus, it seems that the booster vaccination mitigated the differences detected after prime immunization. In contrast to the continued rise of systemic antibodies after booster vaccination, the levels of mucosal IBV-specific immunoglobulin A decreased after booster vaccination. The recruitment or expansion of cluster of differentiation (CD)4⁺, CD8⁺, and CD4⁺/CD8⁺ T-cell populations in different immune effector sites was increased with age, but remained unaltered by IBV vaccination. In contrast, peripheral blood CD4⁺ cells showed a significant increase in IBV-vaccinated chickens compared with nonvaccinated age-matched controls both after primary and booster immunization. The results of the current study confirm that IBV vaccination on the day of hatch induces suboptimal IBV immune responses both in the systemic and mucosal compartments. This routine practice may be contributing to the immunologic escape of the virus and increased persistence of vaccine virus in vaccinated chickens. However, booster vaccination seems to overcome poor initial responses.