The nature of the human erythrocyte "agglutinins" in six selected species of brown algae has been investigated. The "haemagglutinins" are removed by the incorporation of insoluble polyvinylpolypyrrolidone (PVPP) into the extraction medium and cannot be recovered from the PVPP by elution with media containing Tween 80. Protein-rich extracts from the six algae do not contain "agglutinins' 1 for human erythrocytes, but purified polyphenols from four of the six species produce powerful "haemagglutination". Thus the "agglutination" of human erythrocytes by extracts of Ascophyllum nodosum, Fucus serratus, F. spiralis, F. vesiculosus, Himanthalia elongata and Pelvetia canaliculata is considered to be due, principally, to substances which are polyphenolic in nature and quite different from the known lectin-type haemagglutinins in some algae.

Human erythrocytes were exposed to extracts of Codiumfragile ssp. tomentosoides, Ascophyllum nodosum, Dolichos biflorus seeds and a solution of purified polyphenols from Ascophyllum nodosum. In each case the erythrocytes appeared to agglutinate. Agglutinates were examined by scanning electron microscopy. Photomicrographs of the erythrocytes exposed to lectin-containing extracts of C. fragile and D. biflorus showed the typical appearance of agglutinated cells. Photomicrographs of the erythrocytes exposed to the crude extract and purified polyphenols from A. nodosum were similar to each other, but quite different in appearance to erythrocytes agglutinated by the lectins from C. fragile and D. biflorus. This evidence adds further support to the contention that lectin presence recorded in brown algal extracts is largely due to 'pseudoagglutination' produced by polyphenols contained in these extracts.

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