CHARACTERIZATION OF A T-CELL LINEAGE MARKER IN CARP (CYPRINUS-CARPIO L)

A monoclonal antibody against thymocytes (WCL9; of IgG1 class) was pro duced by immunization of mice with isolated membrane molecules of carp thymocytes. Flow cytometric and fluorescence microscopic analysis sho wed that WCL9 was reactive with 30-50% of thymocytes and not with lymp hoid 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 I-week-old fish. Because the WCL9(-) region is more medulla-like, the WCL9(+) cells can be considered as cortical thy mocytes. 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). Immu nogold labelling or comparison of both density fractions did not show clear ultrastructural differences between WCL9(+) and WCL9(-) thymocyt es. The WCL9(-) fraction could be stimulated much better with PHA than the WCL9(+) fraction. Removal of adherent cells or adding adherent ac cessory cells did not influence this result. Immunochemical analysis s howed that WCL9 reacted with a protein determinant present on two mole cules (M-r: 200 and 155 kDa) under reduced and non-reduced conditions. These results, together with the absence of WCL9(+) cells in other ly mphoid organs, strongly suggest that WCL9 is a specific marker for ear ly thymocytes. (C) 1997 Elsevier Science Ltd.