Volume 90, Issue 1, July (2003), pp. 169-178 © The Author 2003
doi:10.1079/BJN2003863

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The oral immunogenicity of BioProtein, a bacterial single-cell protein, is affected by its particulate nature

Hanne R. Christensen¹, Linea C. Larsen¹, Hanne Frøkiær^1
1BioCentrum-DTU, Section for Biochemistry and Nutrition, Technical University of Denmark, DK-2800 Lyngby, Denmark

 (Received 17 July 2002–Revised 3 February 2003–Accepted 11 February 2003)

The bacterial single-cell protein BioProtein (BP; Norferm Danmark, Odense, Denmark), produced by fermentation of natural gas with methanotrophic bacteria, is a potential protein source for man and animals. For human consumption, removal of the nucleic acid is necessary. Preliminary studies have shown that ingested BP induces a specific immune response. The objective of the present study was to characterize the type of response, its development over time and product-related causative factors. Mice were fed with diets containing 60 g nucleic acid-reduced BP/kg, 240 g nucleic acid-reduced BP/kg, 240 g untreated BP (basic BP)/kg or 240 g casein/kg (control). In another study, mice were fed 240 g basic BP/kg, whole cell-free BP-culture homogenate or control diet. The immune response was monitored using an ELISA for BP-specific immunoglobulin in blood and BP-specific immunoglobulin A in blood and saliva. Ingested BP induced a steady specific mucosal and systemic immune response, characterized by a dose-dependent production of immunoglobulin and immunoglobulin A in blood and immunoglobulin A in saliva. Basic BP and nucleic acid-reduced BP induced identical responses. However, feeding mice BP-culture homogenate induced immunoglobulin A in saliva but there was no systemic response. The antibodies from BP-fed mice cross-reacted with BP-culture homogenate revealing the presence of the same antigenic components in the two products despite the different oral immunogenicity. Thus, ingestion of BP induces a persistent mucosal and systemic immune response of which the systemic response can be avoided by ingesting a BP preparation free of whole cells. This indicates the importance of the non-particulate constitution of single-cell protein products intended for human or animal consumption.

Keywords:
Single-cell protein, BioProtein, Oral immunogenicity, Particulate food antigen

Abbreviations:
BP, BioProtein, Ig, immunoglobulin, SCP, single-cell protein, Th, T-helper cell