Evaluation of peripheral lymphocytes after weaning and vaccination for Mycoplasma hyopneumoniae

This study evaluated immune cell populations in pigs following weaning and vaccination for Mycoplasma hyopneumoniae. Piglets (n = 24) were weaned (day 0) at 16 (±1) days of age, and randomly assigned to the vaccination group (n = 16) or control group (n = 8). Complete blood cell counts, flow cytometry and serology were completed for blood samples collected on days 0 (within hours of weaning), 3, 7, 14, 30 and 60. The M. hyopneumoniae S:P ratios (sample optical density: positive control optical density) were negative in the vaccination group until days 30 and 60, when the S:P ratios were 1.3 and 1.0, respectively. Control animals remained serologically negative. The percentage of CD4⁺ T cells was less (P < 0.01) in control pigs than vaccinated pigs at day 3. In contrast, numbers of CD8⁺ and CD4⁺CD8⁺ T cells were greater (P < 0.01) in control pigs than in vaccinated pigs at days 3 and 7. After day 7, few differences in immune cell types were evident between the groups. Differences in lymphocyte populations could not be solely attributed to vaccination, due at least in part, to the confounding influence of weaning. It was difficult to distinguish the influence of vaccination from the impact of weaning on peripheral immune cell populations.