EFFECT OF COLOSTRAL INGESTION ON IMMUNOGLOBULIN-POSITIVE CELLS IN CALVES

The importance of colostrum for passive transfer of maternal immunoglo bulin in calves is well established. Colostrum is thought to have addi tional generalized and antigen-specific immunomodulatory activities, o f which the downregulation of endogenous immunoglobulin production is best documented. The objective of this study was to examine whether in gestion of colostrum altered the B cell subpopulations in the lymph no des of newborn calves, Calves were fed one gallon of either fresh colo strum (Group A, n = 5), milk replacer (Group B, n = 5) or treated (fro zen or irradiated) colostrum (Group D, n = 4) and were euthanized at 3 6-48 h. An additional 5 calves (Group C, 3 newborn and 2 mid-term fetu ses) 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 anti bodies recognizing bovine IgA, IgG1, IgG2, and IgM. Calves from Groups B and C (colostrum deprived, neonates, and fetuses) showed a consiste nt pattern of IgG1 and IgG2 positive cells scattered individually and in clusters throughout lymph node cortex, paracortex, and cortico-medu llary junction. In sharp contrast, no IgG1 and IgG2 positive cells wer e 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 ti ssues of newborn calves in an isotype-specific manner. This results in the elimination of IgG1 and IgG2 positive cells that are present in b oth fetuses and newborn calves. This effect is not eliminated by freez ing or irradiation, indicating that a non-cellular, cold-stable colost ral factor is responsible. Systemically distributed colostral proteins such as immunoglobulin or cytokines are the most likely mediators. Th e significance of this phenomenon in terms of colostral modulation of calf endogenous antibody production is discussed. (C) 1998 Elsevier Sc ience B.V.