Avian leucocyte common antigens: molecular weight determination and flow cytometric analysis using new monoclonal antibodies.

New leucocyte common antigens expressed on all the normal chicken leucocytes have been characterized using two monoclonal antibodies designated as K-11 and K-55. These monoclonal antibodies stained virtually 100% of the leucocytes derived from various lymphoid organs including the spleen, thymus, bursa of Fabricius, caecal tonsil and peripheral blood, as well as a monocytic cell line (MC29), a B cell line (LSCC-RP9), and a T cell line (CU12). However, they did not stain mature erythrocytes, intestinal epithelial cells, or chicken embryonic fibroblasts. The two monoclonal antibodies showed different staining patterns and detected non-overlapping epitopes on MC29 cells in two color immunofluorescence analysis. Western blot analysis under non-reducing conditions showed that the monoclonal antibody K-11 recognized three splenic leucocyte proteins with molecular weights of 92, 42 and 41 kDa, whereas the monoclonal antibody K-55 recognized two proteins with molecular weights of 97 and 42 kDa. The data indicate that the monoclonal antibodies K-11 and K-55 recognize novel leucocyte-common antigens which have lower molecular weights than the previously reported leucocyte-common antigen family.