An immunochemical study of the surfaces of sponge cells

Cells from sponges of six different species when injected into rabbits induced the formation of specific agglutinating antibodies. Cells of each species were shown by cross‐agglutination and cross‐absorption tests to possess species‐specific antigenic determinants on their surfaces, and the observed cross reactions between species were in general accord with taxonomic relationships ascribed on more conventional criteria. Preparations containing complex heteropolysaccharides together with peptide were obtained by extraction of sponges with trichloroacetic acid and were shown to possess the serological specificities of the sponge cell surfaces. These preparations, from each of the six species, sensitized fowl erythrocytes to agglutination by homologous sponge cell antisera. The titers of cross hemagglutination obtained with an individual antiserum and variously sensitized erythrocytes were paralleled by the titers obtained in direct agglutination of sponge cells, indicating that the antigenic groups responsible for hemagglutination were similar to those present on the sponge cell surface and dominating its serological reactions. The isolated polysaccharide‐containing substances precipitated agglutinating antibodies and were themselves antigenic in rabbits. Chemical and serological analysis of a purified polysaccharide obtained from crude material by ion‐exchange chromatography, together with other lines of evidence, suggested that carbohydrate rather than peptide antigenic specificities underlay the serological behaviour of the sponge cell surface. The cell surface specificities detected serologically appeared not to be due to sensitization of sponge cells by intracellular substances liberated during the preparation of cell suspensions from intact sponge. Certain pairs of the sponges examined showed specific cellular reaggregation but the species specificity exhibited did not correlate in any simple manner with the demonstrated antigenic relationships of the species. The serological results are discussed in relation to the various postulated mechanisms of specific reaggregation.