Immunoglobulins on the surface of sheep lymphocytes I. Class and cellular distribution

Sheep immunoglobulins were purified and rabbit antisera specific for μ and γ heavy chains and light chains prepared. Lymphocytes obtained by cannulation of the efferent duct of the sheep popliteal node were labeled in vitro with 125 I‐anti‐Ig antibodies. The percentage of lymphocytes labeling for μ, γ or light chains, was, in each case, approximately 20 – 25 %, but cells were most heavily‐labeled by anti‐μ chain and least by anti‐γ chain antibodies. As the sum of the proportions of cells labeling for μ and γ chains (total, 40.6 %) greatly exceeded that labeling for light chains (20.4 %), it was concluded that labeled cells had both γ and μ chains exposed on their surfaces, probably as IgG and IgM. Lymphocytes were titrated against anti‐μ or anti‐γ chain sera and means (± 1 standard deviation) of 19 200 ± 8200 molecules IgG and 14 700 ± 9300 molecules IgM (19 S, or 73 600 ± 46 800 molecules 8 S) were calculated to be exposed on the surface of each cell labeled by anti‐Ig antibodies. It is suggested that those cells from the sheep which bound anti‐Ig antibodies were bone marrow‐derived lymphocytes as has been found in the mouse.