Feeding heated soyabean flour increases the density of B and T lymphocytes in the small intestine of calves.

The effect of dietary antigens on the gut morphology and density of immune cells was studied in preruminant calves fed milk substitutes containing skim milk powder (SMP), non-antigenic hydrolysed soya protein isolate (HSPI) or antigenic heated soyabean flour (HSF) as their main protein source for 3 months. The height and perimeter of proximal jejunum villi were highest in the calves fed SMP and lowest in those fed HSF (P < 0.05). In contrast, the crypt depth and perimeter were apparently not influenced by the dietary treatments studied. This morphological alteration was associated with a dramatic infiltration of the lamina propria by B and T lymphocytes in the calves fed HSF (P < 0.01). Increased B cell density was essentially accounted for by IgA-, IgG1- and IgG2-bearing cells. The density of CD2-positive T lymphocytes increased (P < 0.01) in the jejunal lamina propria of HSF calves, involving helper (CD4 +) and suppressor-cytotoxic (CD8 +) T cell subsets. The density of gamma-delta (WC1 +) T cells also increased (P < 0.01). The major change concomitantly observed in the villus epithelium was an increased density of CD8 + cells (P < 0.05) and WC1 + cells (P < 0.01).