Immunological relationship between phycoerythrins from various blue-green algae

Rabbit antibodies were prepared against C-phycoerythrin (PE) from a newPseudanabaena species (strain W 1173) and cross-reactivity of this antiserum with phycoerythrins from various blue-green algae was studied. Qualitative immunochemical analysis indicated similarity between the PE's isolated from the species listed in Table 1. No cross-reaction could be detected with phycocynnin. For quantitative immunological studies a viroimmunoassay was developed. Bacteriophage T4 was chemically modified by covalent attachment of PE fromPseudanabaena W 1173. The immunospecific inactivation of this bacteriophage phycoerythrin conjugate can be inhibited by free phycoerythrin, the degree of inhibition being dependent on the immunochemical similarity between the bound and the free antigen. By means of this technique, substantial differences in inhibitory capacity were found between the various PE's, thus showing that the highly sensitive phage technique is able to discriminate between antigenic differences which cannot be detected by immunodiffusion. The degree of antigenic correspondence was also studied by the method of cross-precipitation, which unlike the phage assay requires the heterologous antigen to be multivalent. As expected, the ranges of cross-reactivity obtained by the two procedures were not identical. This result indicates that theamountof cross-reaction observed and the capacity to distinguish between a series of heterologous antigens is affected by the immunochemical method applied. The potential usefulness of the results for taxonomic purposes is discussed.