Immunocyte Populations Observed from Birth to Weaning in Blood, Spleen and Mesenteric Lymph Nodes of Piglets

SIMPLE SUMMARY: Understanding the immunocyte development in neonatal piglets is crucial because susceptibility to pathogen infections and efficacy of vaccination highly depend on the immune status of the piglet. However, the immunocyte information on the period between birth and weaning remains scarce, especially that on immune tissues other than blood, such as mesenteric lymph nodes (MLN) and spleens. Our results indicated that the percentage of innate immunity cells such as myeloid cells, most of them possibly being monocytes, declined from the first day after birth in blood, MLN and spleens. By contrast, other innate immunocytes such as natural killer cells and adaptive immunocytes such as T and B cells were produced while the piglets still suckled in the three organs. Weaning did not seemingly affect the dynamics of the studied immunocytes in a drastic manner, at least during the 14 days post weaning. We foresee that the information from the present study warrants the design of better programs for the administration of vaccines and/or innate immunity stimulators to suckling and weaned piglets. ABSTRACT: Susceptibility to pathogen infections and efficacy of vaccination highly depend on the immune status of the piglet. Here, we measured immunocytes in piglets from birth to weaning to elucidate how immunocyte populations change during development and are affected by weaning. Crossbred piglets were used. Suckling piglets were euthanized at 1, 7, 14, 21, 28 or 35 days old (3~4 piglets at each time point). In addition, seven piglets were weaned at 21 days old, with four being euthanized at 28 days old and the remaining at 35 days old. Piglet carcasses were dissected, and blood, mesenteric lymph nodes (MLN) and spleen were sampled. In total, seven antibodies were used to stain the immunocyte population. Dynamics of myeloid (CD3(–)SWC3(+)CD16(+)), natural killer (NK; CD3(–)SWC3(–)CD16(+)), killer T (CD3(+)CD8(+)), helper T (CD3(+)CD4(+)) and B (CD3(–)CD21(+)) cells were analyzed. Percentage of innate immunity cells such as myeloid cells declined (p < 0.05) from the first day after birth. In contrast, percentage of NK cells increased in piglets while they were still suckling. Killer T, helper T, and B cell populations increased around 2~3 weeks after birth. No significant differences in the populations of the evaluated cell types were observed between suckling and weaned piglets at least for 14 days post weaning.