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Isolation of Bovine Immunoglobulins Resistant to Peptic Digestion: New Perspectives in the Prevention of Failure in Passive Immunization of Neonatal Calves

A. C. R. C. Porto^*, L. L. Oliveira^*, L. C. Ferraz^*, L. E. S. Ferraz^*, S. M. O. Thomaz^*, J. C. Rosa^*, and M. C. Roque-Barreira^*

^* Departamento de Biologia Celular e Molecular e Bioagentes Patogênicos, and
Centro de Química de Proteínas, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes 3900, 14049-900 Ribeirão Preto, São Paulo, Brazil

¹ Corresponding author: mcrbarre{at}fmrp.usp.br

In calves, neonatal mortality and disease susceptibility are greatly influenced by failure in passive immunization, normally provided by colostrum ingestion just after birth. Formulations projected to replace natural colostrum have not been successful, and one of the possible reasons for such failure is that orally administered Ig are probably digested in the gastrointestinal tract, so they are not absorbed as intact functional molecules. With the aim of finding an adequate colostrum substitute, we used columns of immobilized jacalin, a lectin known by its ability to bind O-linked oligosaccharides, to obtain a colostral Ig population putatively protected against enzymatic cleavage by the presence of sugar chains. Immunoglobulin G₁ is a major constituent of colostrum Ig bound to jacalin (JB-Ig). This preparation contains 10% of the total colostral Ig and is typically 3 to 6 times more resistant to pepsin digestion than the Ig contained in the fraction that is not bound to jacalin, which presumably does not contain O-glycans. Mass spectrometry analysis demonstrated that the tryptic peptides obtained from JB-Ig and unbound Ig were similar, indicating that their distinct susceptibility to enzyme hydrolysis was associated with differences in their sugar chains. Therefore, the present research suggests that the bovine colostrum JB-Ig has potential application in the immunotherapy of neonatal calves that have not been supplied with colostrum.

Key Words: bovine colostrum • immunoglobulin • jacalin • peptic digestion

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