LOCAL AND SYSTEMIC IMMUNE-RESPONSES TO SOYBEAN PROTEIN INGESTION IN EARLY-WEANED PIGS

The development of local and systemic immune responses to soybean prot eins was investigated in early-weaned pigs. Pigs were given either ant igenic (ASP, n = 10 pigs) or non-antigenic (NASP, n = 8 pigs) soybean products (6 g of protein/d) from d 5 to 9 of age by stomach tube. Afte r weaning at d 21, pigs were fed diets containing the corresponding so ybean products and slaughtered between d 28 to 30. Diarrhea was 2.4-fo ld more frequent, the size of duodenal villi was reduced by 24 to 36%, and the eosinophil density in the duodenal mucosa was 13 times greate r(P < .02) in the ASP pigs compared with the NASP pigs. A larger eryth ema area (P = .006) was observed in the ASP group than in the NASP gro up 30 min after an intradermal injection of glycinin, but no significa nt difference could be detected with alpha- or beta-conglycinin or who le soybean of the protein fractions and of the mechanisms extracts. No difference in skin fold thickness was apparent between groups 24 h la ter. Intestinal, mesenteric lymph node, and blood lymphocytes did not proliferate when cultured with soybean proteins, regardless of dietary treatment. By ELISA, no difference between groups was observed in the circulating levels of total immunoglobulins (Ig) and IgM. Immunoblott ing patterns of raw soybean with sera from 28-d-old pigs showed two ba nds (22 and 36 kDa) recognized by IgA and IgM, respectively, in the AS P group only. Finally, the adverse effects observed with antigenic soy bean flour can be overcome by the use of alcohol-treated products. How ever, a better knowledge of the protein fractions and of the mechanism s involved is still required to achieve non-antigenic products of high er market value.