Yeast β-Glucans as Fish Immunomodulators: A Review

Abstract

Administration of immunostimulants in fish is a preventive method to combat infections. A wide variety of these biological molecules exist, among which one of the yeast wall compounds stands out for its different biological activities. The β-glucan that forms the structural part of yeast is capable of generating immune activity in fish by cell receptor recognition. The most frequently used β-glucans for the study of mechanisms of action are those of commercial origin, with doses recommended by the manufacturer. Nevertheless, their immune activity is inefficient in some fish species, and increasing the dose may show adverse effects, including immunosuppression. Conversely, experimental β-glucans from other yeast species show different activities, such as antibacterial, antioxidant, healing, and stress tolerance properties. Therefore, this review analyses the most recent scientific reports on the use of yeast β-glucans in freshwater and marine fish.

Keywords: biomolecules; functional carbohydrates; immunity; infectious diseases.

Figure 1

Conformation of the yeast cell wall. The cell wall is the largest, most resistant, and rigid organelle affecting the interaction with the external environment and the protection of the intracellular organelles, where compounds of great biotechnological interest are found including β-glucans.

Figure 2

Representative scheme of the methods used for β-glucan extraction from yeast. Methodologies used for β-glucan extraction from yeast mainly differ in the method of breaking down the cell wall to release the internal components, and in the use of organic solvents to separate them. Finally, a purification process by centrifugation and chromatography is performed to obtain β-glucan from yeast.

Figure 3

Signaling pathway for yeast β-glucans in teleost fish organisms. Proposed scheme of the β-glucan activation pathway in fish. (1) Intestinal epithelial enterocytes synthesize metabolic proteins activated by yeast β-glucan that secretes them into the systemic circulation. (2) Recognition of β-glucan by pathogen-associated molecular pattern receptors (PAMPs) that generate innate cellular immune responses and gene expression through translocation of the nuclear factor kappa beta (NF-κB) by phosphorylation, ubiquitination, and protein degradation. (3) Production of pro- and anti-inflammatory cytokines, receptors, and other proteins that activate the communication and activity of the adaptive immune system. (4) Production of immunoglobulins by B cells activated by the recognition of β-glucan.