In pigs, the epitheliochorial placenta does not allow transfer of maternally derived antibodies or immune cells to the fetus. Thus, piglets are dependent on intake of colostrum for acquisition of passive immunity during the neonatal period. As well as immunoglobulin G (IgG), cellular components of colostrum, mainly lymphocytes, can enter the systemic circulation and secondary lymphoid organs of the neonate. In order to understand the function and immunological role of these cells, a flow cytometric study was undertaken to characterise the cellular profile and phenotype of T cells and NK cells present in porcine colostrum. The results indicated that the greatest numbers of lymphocytes were found on the first day of lactation. The predominant cell types in colostrum were CD8(+) single positive T cells (53.6%), followed by CD4(+)CD8(+) double positive T cells (21.1%), CD2(+)CD8(+) γδ T cells (15.0%) and NK cells (13.5%). CD4(+) single positive T cells (4.4%) and other γδ T cell subpopulations (1.8% CD2(-)CD8(-) and 0.4% CD2(+)CD8(-)) were present in colostrum at low levels. Although the profile of the T cell subpopulations during the first 3 days of lactation remained constant, the absolute numbers of T and NK cells decreased significantly in the first few hours of lactation. Expression of CCR7, CD11b, CD25, CD45RA and MHC class II was used to assess the activation status of T and NK cells in colostrum. T cell subpopulations expressed markers consistent with an effector memory phenotype, indicating that these were antigen-experienced cells. The phenotype of colostral T and NK cells suggests a role in mucosal immunity and potentially in transfer of passive immunity from sow to piglet.

Department of Immunology Veterinary Research Institute Hudcova 70 621 00 Brno Czech Republic

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