Abstract: Taking into account the role played by the neuroendocrine network in affecting the early development of the immune response, the present study aims to assess neonatal immunity in piglets by testing peripheral lymphocyte age-related changes in relationship to plasma levels of some relevant immunoregulatory hormones, such as growth hormone (GH), prolactin (PRL) and cortisol. For this purpose, we studied the peripheral lymphocyte age-related changes in relationship to plasma levels of GH, PRL and cortisol in conventional piglets from birth (day 0) to 41 days of age. A significant decrease was observed in the total number of lymphocytes at day 0, with a subsequent constant increment up to 41 days of age. Concomitantly, the number of T cell subsets (mainly CD8(+) cells and double positive CD4(+)CD8(+)) was low at birth, with strong increments between the 19th and 41st days of life. The CD4(+) T cell number subset was less diminished at birth than that of CD8(+), albeit with significant increments in the post-weaning period. Of interest, gammadelta T cells, which are more involved in innate immune efficiency, displayed the same trend as CD8(+) T cells from birth to the 41st day of life. From day 0 up to the 19th day, significant inverse correlations were found between T cell subsets and GH or PRL or cortisol, albeit with more significant inverse correlations with cortisol. The high levels of GH and PRL in the pre-weaning period may be due to the fact that they have to counteract the cortisol-mediated negative effect on lymphocyte production and development. These findings suggest that stress condition occurs at birth with decreases in the immune parameters, in the same way as in human newborns, with a subsequent gradual normalisation and immune development, as shown by decreased cortisol, GH and PRL normalisation and concomitant increments in T cell subsets.
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