Effect of colostral ingestion on immunoglobulin-positive cells in calves.

The importance of colostrum for passive transfer of maternal immunoglobulin in calves is well established. Colostrum is thought to have additional generalized and antigen-specific immunomodulatory activities, of which the downregulation of endogenous immunoglobulin production is best documented. The objective of this study was to examine whether ingestion of colostrum altered the B cell subpopulations in the lymph nodes of newborn calves. Calves were fed one gallon of either fresh colostrum (Group A, n = 5), milk replacer (Group B, n = 5) or treated (frozen or irradiated) colostrum (Group D, n = 4) and were euthanized at 36-48 h. An additional 5 calves (Group C, 3 newborn and 2 mid-term fetuses) did not receive any feedings; the neonatal calves were euthanized immediately following birth. Mesenteric and regional lymph nodes from all calves were analyzed by immunocytochemistry using monoclonal antibodies recognizing bovine IgA, IgG1, IgG2, and IgM. Calves from Groups B and C (colostrum deprived, neonates, and fetuses) showed a consistent pattern of IgG1 and IgG2 positive cells scattered individually and in clusters throughout lymph node cortex, paracortex, and cortico-medullary junction. In sharp contrast, no IgG1 and IgG2 positive cells were present in the lymphoid tissues of colostrum fed calves (Groups A or D). Numbers of IgM and IgA positive cells were similarly distributed in all calf groups. These findings demonstrate that colostrum feeding reduces the number of immunoglobulin positive cells in the lymphoid tissues of newborn calves in an isotype-specific manner. This results in the elimination of IgG1 and IgG2 positive cells that are present in both fetuses and newborn calves. This effect is not eliminated by freezing or irradiation, indicating that a non-cellular, cold-stable colostral factor is responsible. Systemically distributed colostral proteins such as immunoglobulin or cytokines are the most likely mediators. The significance of this phenomenon in terms of colostral modulation of calf endogenous antibody production is discussed.