Studies on the Immobilization Antigens of Paramecium. IV. Properties of the Different Antigens.

serum, but not by antiserum made against other serotypes. The complex cytoplasmic, genic, and environmental factors that determine which of the possible serotypes is manifested in a given animal were discovered by SONNEBORN (1948). The inheritance of serotypes in Paramecium has been reviewed recently by BEALE (1957). Animals of each serotype contain a single characteristic protein or immobilization antigen which is localized primarily in the cilia and body wall. The specificity of most, if not all, of the immobilization antigens is determined by the alleles at several different loci-one locus being responsible for the specificity of each serotype. Since individual cells generally show only one serotype at a time, only m e genetic locus comes to expression at a time. Within a stock serotypic differences are determined either by the environment or by cytoplasmic inheritance. In the first paper of this series (PREER 1959a) it was shown how the immobilization antigens can be followed quantitatively in uitro using antigen-antibody precipitation in agar gel. PREER (195913) has recently shown how the antigens can be isolated chemically, and finally PREER (1959~) gave an account of the properties of antigen A of stock 51. I t was found that the A antigen is a large asymmetric protein molecule with a molecular weight of around a quarter of a million. The present and last paper of the series deals with a comparative study of several of the immobilization antigens of syngens (varieties) 2 and 4 of Paramecium aurelia. Serology, solubility in ammonium sulfate, and, to a lesser extent, sensitivity to proteolytic enzymes have been studied. F J types or serotypes. Each serotype is immobilized by its homologous anti-