IGM, IGA, IGG1 AND IGG2 SPECIFIC RESPONSES IN BLOOD AND GUT SECRETIONOF CALVES FED SOYBEAN PRODUCTS

Calves fed soya proteins may develop severe gastrointestinal disorders . Whether these are predominantly associated with particular Ig subcla sses and (or) dietary proteins remains unclear. Therefore, antibody re sponses to soyabean protein were analysed by dot- and blot-immunobindi ng in plasma and intestinal mucous secreations. One-month-old calves w ere fed for 2.5 months liquid diets based on skim milk powder (SMP) or a mixture (2:3, protein basis) of whey and soyabean products includin g a low antigenic hydrolysed soya protein isolate (HSPI) and a highly antigenic heated soya flour (HSF). Specific antibodies (Abs) of the ma in isotypes (IgM, IgA, IgG1, IgG2) were characterised by immunostainin g of samples which had been previously incubated with nitrocellulose s heets coated with SMP, HSPI or HSF extracts. Plasma collected before f eeding experimental diet showed very little specific Abs. By contrast, 2.5 months later, a three-fold increase (p<0.05) in IgG1 and IgA titr es against HSF antigens was observed in calves fed HSF compared with t hose fed the control or HSPI diet. IgG1 immunoblotting revealed many p rotein bands from soya in the molecular range of 22-32 and 38-42 kDa. Immuno-recognition of specific proteins from SMP and HSPI remained low and similar among animal groups. Specific IgM, IgA and IgG1 titres ag ainst HSF, and to lesser extent HSPI, were significantly higher (P<0.0 5) in jejunal mucous secreation of calves fed HSF compared with other groups. Secreations from calves fed HSF bound to many soyabean protein s in the range of 17-23 and 26-38 kDa, with similar patterns for IgA a nd IgG1. By contrast, only weak bands were found for IgM and IgG2 in a ll groups of calves. Thus, calves fed antigenic HSF do present specifi c Abs including IgG1 and IgA isotypes, both systemically and locally. Therefore, IgG1 and (or) IgA rather than IgM and IgG2 Abs may be prefe rred for assessing the immunogenicity of soyabean products in calves. Interestingly, soyabean immunogenicity was drastically reduced by adeq uate proteolysis.