Monoclonal antibodies inhibiting mating reactivity exclusively of odd mating types in Paramecium caudatum

Abstract

Summary Paramecium caudatum has the bipolar system of mating types and thus each syngen consists of two complementary mating types, even and odd types. Mating types are distinguished by the agglutination reaction when complementary mating types are mixed, but the substances (called the mating type substance) involved in specific cell recognition between complementary mating types have not so far been identified as the molecules in Paramecium. To identify the mating type substances we obtained 5 monoclonal antibodies inhibiting the mating reactivity of odd mating type of syngen 3. Cilia detached from the highly reactive odd mating type, pretreated with salt alcohol, were injected into mice and 5 monoclonal antibodies (OmA, OmB, OmC, OmD and OmE) were obtained after screening. All of them inhibited mating reactivity of all odd strains of syngen 3 examined but of no even strain without inhibiting action on the ciliary movement. Among 7 other syngens than syngen 3, cross reactivity in inhibition of mating reactivity, against odd types was observed to some degree in syngen 1, 5, 13, but not in syngen 4, 6, 12 when the four antibodies except OmB were used. Thus, the inhibiting action has no syngen specificity. Localization of the antigen recognized by these antibodies was examined by indirect immunofluorescence. Immunofluorescence was observed on the cilia of the ventral surface, mostly in the anterior tip which is known to be reactive in mating clump formation, and looked like beads in a line on the surface of the cilia. The mating type specificity of the inhibiting action and the localization on the cell strongly suggest that these antibodies recognize the mating type substances.