Ultrastructural studies of human lymphoid cells. mu and J chain expression as a function of B cell differentiation.
J chain expression was examined as a function of the stage in differentiation along the B cell axis in humans. Intracellular distribution of J and mu chains in leukemic HLA-DR+ null and pre-B cells, and in normal B cells stimulated with pokeweed mitogen (PWM) was determined by immunoelectron microscopy and radioimmunoassay (RIA). J chain was detected in leukemic null and pre-B cells on free and membrane-bound ribosomes in the cytoplasm, or on perinuclear cisternae. Mu chain was found on free ribosomes and ribosomal clusters in leukemic pre-B cells but was absent in the leukemic null cells. In pre-B cell lines, mu chain was seen within rough endoplasmic reticulum (RER) and the Golgi apparatus whereas J chain was not detected in these organelles. However, both mu and J chain were detected in RER and the Golgi apparatus of immature and mature plasma cells induced by PWM stimulation of normal peripheral blood lymphocytes. Low levels of J chain were also detected by RIA in lysates of leukemic null and pre-B cells. Most of the intracellular J chain became detectable after reduction and alkylation of cell lysates, and free J chain was not found in the culture supernatants. The amount of intracellular and secreted immunoglobulin-bound J chain increased dramatically after PWM stimulation of peripheral blood lymphocytes. The majority of J chain-positive cells seen over an 8 d culture interval were lymphocytes and lymphoblasts, while mu chain was found primarily in plasma cells. These results suggest that J chain expression precedes mu chain synthesis during B cell differentiation and that a combination of the two chains for secretion is not initiated until the onset of plasma cells maturation.
D001402:B-Lymphocytes / Q000648:ultrastructure*; D001854:Bone Marrow Cells; D002454:Cell Differentiation; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000648:ultrastructure; D006801:Humans; D007143:Immunoglobulin Heavy Chains / Q000032:analysis*; D007144:Immunoglobulin J-Chains / Q000032:analysis*; D007148:Immunoglobulin mu-Chains / Q000032:analysis*; D007945:Leukemia, Lymphoid / Q000473:pathology; D008213:Lymphocyte Activation; D008854:Microscopy, Electron; D011863:Radioimmunoassay; D012270:Ribosomes / Q000032:analysis
D007143:Immunoglobulin Heavy Chains; D007144:Immunoglobulin J-Chains; D007148:Immunoglobulin mu-Chains