Ontogeny and characterization of blood leukocyte subsets and serum proteins in piglets before and after weaning

Existing knowledge about the development of the porcine immune system was extended by phenotypic characterization of leukocyte subsets and with assessment of Mannan-Binding Lectin (MBL) and immunoglobulin concentrations in peripheral blood of healthy piglets. Single-color and/or double-color flow cytometry using monoclonal antibodies against CD1, CD3, CD4, CD8a CD14, CD21, CD172 (SWC3a), CD284 (TLR4), SLA I, and SLA II were performed to identify T-lymphocyte subsets, B-lymphocytes, monocytes, and granulocytes. ELISA was used to measure the concentration of serum proteins. Several of the analyzed parameters seem to be affected at the time of weaning which took place at 4–5 weeks of age. Using principal component analysis, all analyzed variables – except one – were grouped into 8 factors with distinct developmental profiles. Several of these factors revealed an apparent suppression, a steady state or an acceleration of the developmental age profiles around weaning. In conclusion, results indicate that weaning suppresses a broad spectrum of adaptive immune variables and that this was evident immediately after weaning as well as after a lag period of about one week. On the contrary, variables of the innate immune system seem to be stimulated immediately after weaning. At the time considered to have the highest infection pressure T-cells and TLR4+ cells were markedly enhanced, whereas the expression of SLA I did not seem to be affected by weaning.