Local and Systemic Immune Responses in Growing Feather Pulps and Blood of Broiler Chickens Elicited by Electron Beam- and Formalin-Killed Staphylococcus aureus Vaccines.

BACKGROUND

Staphylococcus aureus (SA) causes septicemia and arthritis, eventually resulting in substantial economic losses and health hazards in poultry. Lethal electron beam (eBeam) treatment kills bacteria while preserving surface epitopes.

METHODS

This study compared broiler chicken immune responses (local and systemic) after eBeam-killed (eB) or formalin-killed (FK) SA injections. The vaccine (sham) control was endotoxin-free PBS. This study contained six treatments (trt) with five chickens/trt, with vaccine trts divided into two groups, A and B. Group A received in ovo vaccine/sham treatments (phase 1) initially. At 34 d of age, the pulps of growing feathers (GFs) received intradermal (i.d.) injections of the respective trt to elicit booster and primary responses in groups A and B, respectively. Blood was collected to analyze leukocyte populations and plasma SA-specific antibody levels. Additionally, in phase 2, GFs were collected to assess leukocyte presence in GF pulps. Two-way ANOVA was conducted to test the effects of treatment, time, and their interactions, followed by Tukey's HSD tests at p < 0.05 for statistical significance.

RESULTS

Early in phase 1, the eB group had increased SA-specific IgM, IgA, and total lymphocyte concentrations compared with FK. In phase 2, FK and eB i.d. vaccines increased total lymphocyte and T cell proportions in GF pulps compared with sham. In blood, the recall eB vaccination increased monocytes, B cells, CD8+ T cells, and total lymphocytes, while the recall FK vaccination increased heterophils (p < 0.05).

CONCLUSIONS

Improved early protection at mucosal surfaces may be reflected by higher plasma levels of SA-specific IgM and IgA following in ovo eBeam-killed-SA vaccination. Additionally, both eB-SA and FK-SA vaccines stimulated robust local inflammatory responses dominated by lymphocytes in GF pulps.