Two distinct antigens on chicken thymocytes defined by monoclonal antibodies

Two distinct antigens expressed on chicken thymocytes were defined by monoclonal antibodies designated as Lc-1 and Lc-2. Lc-1 (IgGl) reacted with 80% of the thymocytes (mostly cortical and medullary thymocytes) and Lc-2 (IgM) reacted with 40% of the thymocytes (mainly cortical thymocytes). Lc-1 reacted with 1% of the spleen lymphocytes, but the antibody was nearly nonreactive with cells from peripheral blood leukocytes, bursa and bone marrow. Lc-2 reacted with only small percentages of spleen and bursa cells, and with very few cells from peripheral blood leukocytes and bone marrow. This antibody reacted with a portion of concanavalin A stimulated spleen lymphocytes. When Marek's disease-derived T-lymphoblastoid cell lines were tested for their reactivities with monoclonal antibodies, Lc-1 reacted with none of the cell lines tested, whereas Lc-2 reacted with four of the six cell lines tested. Antigens recognised by Lc-1 and Lc-2 were first found in chick embryonic thymus on day 13 of incubation, after which the number of cells positive for Lc-1 and Lc-2 rapidly increased, reaching young adult levels by days 15 and 14 of embryonic life, respectively. Lc-1 precipitated materials with apparent molecular weights of 60 and 120 kDa from radioiodinated thymocytes.