Specificity of a Beta-glucan Receptor on Macrophages from Atlantic Salmon (Salmo Salar L.)

This study was undertaken to study the specificity of a beta-glucan receptor on Atlantic salmon macrophages. Previous in vitro studies have shown that Atlantic salmon macrophages express a receptor that rapidly recognizes and mediates uptake of nonopsonized beta-glucan particles. The ingestion of particles was shown to be inhibited by preincubating the macrophages with glucans containing beta-1,3-linkages, but not by glucans containing other linkages. In the present study we have shown that small oligomers from formolyzed beta-glucan particles, and linear beta-1,3-linked oligomers with a degree of polymerization (DP) > or = 3, were efficient inhibitors of uptake of glucan particles. Oligomers from beta-1,6-linked pustulan, or small size oligomers with linkages other than beta-1,3, were not able to inhibit uptake of glucan particles. The inhibitory effect of laminarin and laminariheptaose was abolished by degrading the nonreducing terminal ends by sodium periodate treatment. The inhibitory effect of laminarin was regained by a complete Smith degradation; that is, periodate oxidation followed by reduction and hydrolysis. Modification of the reducing end of laminariheptaose had no effect on its ability to inhibit uptake. Furthermore, it was shown that periodate-oxidized glucan particles were not taken up by salmon macrophages, and that the uptake was regained when the particles were hydrolyzed to recover the nonreducing terminal end. Lastly, it was shown that endo-beta-1,6-glucanase treatment of the yeast glucan particles did not reduce uptake, confirming that beta-1,6-linkages are not involved in the recognition. These results suggest that Atlantic salmon macrophages possess a receptor that may recognize even very short beta-1,3-linked glucosyl chains extending from yeast cell walls.