title: Quantitative ultrastructural autoradiographic studies of iodinated plasma membranes of lymphocytes during segregation and internalization of surface immunoglobulins.
abstract: Rat spleen lymphocytes were iodinated (125 I) with lactoperoxidase. Quantitative autoradiographic studies on cells fixed immediately after iodination showed 19-24% of intracytoplasmic grains at 3HD and over from the plasma membrane. Normalization of grain density distribution and comparison of resulting curves with the universal curve of grain scatter of 125 I showed that a significant percentage of intracytoplasmic grains (36%) originates from intracytoplasmic labeled sources rather than from scattering from the heavily labeled plasma membrane. Damaged cells had a threefold grain density than intact cells. Radioactivity counts in sliced polyacrylamide gels of iodinated cells revealed 65-72% of total radioactivity in five peaks of apparent mol wt of 44, 50, 57, 90 and 195 thousand daltons. Segregation and internalization of anti-immunoglobulin-Ig-horseradish peroxidase (HRP) complexes from the iodinated plasma membrane proteins of lymphocytes was studied with quantitative autoradiography (125 I) and peroxidase cytochemistry; 64% of grains at 1.5HD (1,500 A) from the plasma membrane were within the cap zone, and 36% of grains remained outside the capped immunoglobulins; 45-57% of grains internalized together with Fab-anti-Ig-Ig-HRP, and 68% of grains internalized together with anti-Ig-Ig-HRP. These studies indicate that (a) iodination of rat spleen lymphocytes results in a significant internal labeling and that (b) immunoglobulins segregate into caps and internalize together with other iodinated plasma membrane proteins while a significant percentage of iodinated proteins (36%) are excluded from the immunoglobulin caps or internalization sites (32-55%).
mesh_terms: D000818:Animals; D001345:Autoradiography; D002462:Cell Membrane / Q000276:immunology / Q000648:ultrastructure*; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis; D006651:Histocytochemistry; D006735:Horseradish Peroxidase; D007455:Iodine; D007784:Lactoperoxidase; D008214:Lymphocytes / Q000276:immunology / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D011947:Receptors, Antigen, B-Cell
chemical_list: D011947:Receptors, Antigen, B-Cell; D007455:Iodine; D006735:Horseradish Peroxidase; D007784:Lactoperoxidase