Immunoglobulins on the surface of sheep lymphocytes. ii. class, size and fate during incubation of lymphocytes at 37 °c

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Abstract
Sheep lymphocytes possessing surface Ig were labeled with 125I‐labeled anti‐Ig antibodies. The radioactive complexes thus formed were dissolved from the cell membrane by treatment with the detergent Nonidet‐P40 and their molecular sizes estimated by sedimentation centrifugation. IgG and IgM (20–40 % as 19 S IgM) were shown to be present on the cell surface.Cells labeled with anti‐Ig antibodies and incubated at 37 °C lost 30–40 % of their radioactivity within 30–45 min, after which time the rate of loss decreased. By 3–4 h, approximately 50 % had been released and loss had almost stopped. Label associated with surface‐bound anti‐sheep lymphocyte globulin was also lost rapidly (20–30 % in 30 min), but unlike anti‐Ig antibodies, no further loss occurred. Anti‐Ig complexes retained by labeled cells during incubation at 37 °C were steadily degraded to a 3–4 S component. Sodium azide (0.015 M) significantly reduced the rate at which this degradation occurred (e.g. inhibition relative to degradation in the absence of azide was 94 % after 2 h and 67 % after 4 h incubation, respectively).When unlabeled lymphocytes were incubated at 37 °C for up to 20 h and then reacted with labeled anti‐Ig, the following was observed. The proportions of lymphocytes able to bind anti‐γ or anti‐μ‐chain antibody (as judged by autoradiography) decreased from 17 % to 3 % and 28 % to 18 %, respectively, during 20 h incubation. From measurements of Ig released during incubation, it was concluded that most of the IgG initially on cells binding anti‐γ‐chain antibody was probably cytophilic. IgM initially on the surface of cells binding anti‐μ‐chain antibody seemed to be released and replaced by the cells, although a small proportion may have been cytophilic.