POST-VACCINATION IMMUNOLOGICAL RESPONSE IN SMALL RUMINANTS: A COMPARATIVE FIELD STUDY OF COMMERCIAL VACCINES

Abstract

The study determined the immunological response of small ruminants after vaccination with live-attenuated, inactivated, and subunit-commercial vaccines.  A total of 120 sheep and goats were registered and equally assigned to each vaccine group. Their hematological, humoral, cellular, cytokine, and innate immune systems were thoroughly evaluated.  Total white blood cell counts (12.8 ± 1.2 x10 3 /uL), lymphocyte counts (62.3 +/- 6.0%), and neutrophil counts (55.7 +/- 5.6%) were significantly higher in the live-attenuated vaccine group as compared to the other groups (p < 0.001).  The live-attenuated group showed the highest antibody titer on day 28 (96.8 +/- 7.5 ELISA units) and the IgG response remained at the same level until day 90.  Live-attenuated vaccines induced a significant expansion of both the CD4+ (1050 ± 80 cells/l) and CD8+ (750 ± 65 cells/l) T cell populations (p < 0.001) that correlated strongly with antibody titers (r = 0.72, p < 0.001).  The cytokine analysis revealed that the level of IFN- 7 was high (42.8 +/- 4.5 pg/mL) indicating that the activation of Th1 was intense. Conversely, IL-4 concentration was greater in individuals that received the subunit vaccine (24.7 ± 2.8 pg/mL) and this indicated that the immune response was skewed towards humoral immunity.  The regulatory cytokines IL-10 and TGF -b were moderately elevated in all the vaccinated groups.  As an intrinsic biomarker, the activity of lysozyme was significantly higher in the live-attenuated subjects (15.6 ± 1.5 U/mL).  Logistic regression analysis demonstrated that live-attenuated vaccines (OR = 5.62), IFN- 7 levels (OR = 3.74), and CD4+ count (OR = 2.85) are important predictors of a strong immune response (p < 0.001).  All these data suggest that live-attenuated vaccines are better and confer more broad-spectrum immunity by combining robust humoral, cellular, and innate immunity, and should be a priority to achieve optimal disease prevention in small ruminants