Characterization of a T cell lineage marker in carp (Cyprinus carpio L.)

A monoclonal antibody against thymocytes (WCL9; of IgG1 class) was produced by immunization of mice with isolated membrane molecules of carp thymocytes. Flow cytometric and fluorescence microscopic analysis showed that WCL9 was reactive with 30-50% of thymocytes and not with lymphoid cells from blood, pronephros, spleen and intestine. Cryo-sections of thymus showed a WCL9+ and WCL9- region in 3-month-old fish and only WCL9+ cells in 1-week-old fish. Because the WCL9- region is more medulla-like, the WCL9+ cells can be considered as cortical thymocytes. The majority of WCL9+ thymocytes appeared to have a higher density (1.06-1.07 g/mL) than the WCL9- cells (1.02-1.06 g/mL). Immunogold labelling or comparison of both density fractions did not show clear ultrastructural differences between WCL9+ and WCL9- thymocytes. The WCL9- fraction could be stimulated much better with PHA than the WCL9+ fraction. Removal of adherent cells or adding adherent accessory cells did not influence this result. Immunochemical analysis showed that WCL9 reacted with a protein determinant present on two molecules (M(r): 200 and 155 kDa) under reduced and non-reduced conditions. These results, together with the absence of WCL9+ cells in other lymphoid organs, strongly suggest that WCL9 is a specific marker for early thymocytes.