SPECIFICITY OF A BETA-GLUCAN RECEPTOR ON MACROPHAGES FROM ATLANTIC SALMON (SALMO-SALAR L)

This study was undertaken to study the specificity of a P-glucan recep tor on Atlantic salmon macrophages. Previous in vitro studies have sho wn that Atlantic salmon macrophages express a receptor that rapidly re cognizes and mediates uptake of nonopsonized beta-glucan particles. Th e ingestion of particles was shown to be inhibited by preincubating th e macrophages with glucans containing beta-1,3-linkages, but not by gl ucans containing other linkages. In the present study we have shown th at small oligomers from formolyzed beta-glucan particles, and linear b eta-1,3-linked oligomers with a degree of polymerization (DP) greater than or equal to 3, were efficient inhibitors of uptake of glucan part icles. Oligomers from beta-1,6-linked pustulan, or small size oligomer s with linkages other than beta-1,3, were not able to inhibit uptake o f glucan particles. The inhibitory effect of laminarin and laminarihep taose was abolished by degrading the nonreducing terminal ends by sodi um periodate treatment. The inhibitory effect of laminarin was regaine d by a complete Smith degradation; that is, periodate oxidation follow ed by reduction and hydrolysis. Modification of the reducing end of la minariheptaose had no effect on its ability to inhibit uptake. Further more, it was shown that periodate-oxidized glucan particles were not t aken up by salmon macrophages, and that the uptake was regained when t he particles were hydrolyzed to recover the nonreducing terminal end. Lastly, it was shown that endo-beta-1,6-glucanase treatment of the yea st glucan particles did not reduce uptake, confirming that beta-1,6-li nkages are not involved in the recognition. These results suggest that Atlantic salmon macrophages possess a receptor that may recognize eve n very short beta-1,3-linked glucosyl chains extending from yeast cell walls.